{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#1F1F1F","name":"user"}}],"text":"今日分享開始啦，請大家多多指教~","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"一、初識異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"經常有同學看到異常來問了，異常到底是什麼？ 而在我們之前的學習中，我們其實已經接觸到了Java當中的異常。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"1.算數異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首先我們遇到的第一個異常是我們在講除號運算符時遇到的——算數異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"見以下代碼","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/1f/1f8d47d282c6ef7f2d82f18733444716.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們在分子的位置出現了0，來運行以上代碼。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ac/ac060dccfff8e8751fd2ba837a0a114e.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"2.數組下標越界異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在數組篇我們也提到了數組越界的問題","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看以下代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f0/f0ea7620deebee4dfa6e72040988e315.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行時結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/db/db6bd333784ecf144810fc347dbca082.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"查看異常的信息","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/78/781acba2a0e534bd7be72bd1c74c2e79.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"3.空指針異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"空指針異常也在之前的學習中經常出現","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"看以下代碼","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/da/da3f8346ede29b8d6fef6f30713f96ca.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們將 array 數組置爲 null ，之後再去訪問這個數組，就出現了空指針異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/50/50f5f6ce2e283e5b84b168dab7c172c7.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這些異常都是需要我們在平時所積累出來的，所謂異常指的就是程序在運行時出現錯誤時通知調用者的一種機制。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"關鍵字 “運行時”","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有些錯誤是這樣的，例如將 System.out.println 拼寫錯了，寫成了 system.out.println. 此時編譯過程中就會出錯，這是 “編譯期” 出錯。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"而運行時指的是程序已經編譯通過得到 class 文件了，再由 JVM 執行過程中出現的錯誤。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"4.異常的處理方式","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"異常的種類有很多，不同種類的異常具有不同的含義，也有不同的處理方式。（在此瞭解即可）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}},{"type":"strong","attrs":{}}],"text":"防禦式編程","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"錯誤在代碼中是客觀存在的，因此我們要讓程序出現問題的時候及時通知程序猿，我們有兩種主要的方式。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"LBYL: Look Before You Leap.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在操作之前就做充分的檢查。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"EAFP: It’s Easier to Ask Forgiveness than Permission.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"“事後獲取原諒比事前獲取許可更容易”，也就是先操作，遇到問題再處理。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"其實很好理解，打一個非常形象的比喻來理解啊：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"比如說有一個你非常喜歡的女生，你想要去拉她的手，那麼有幾種方式呢?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第一種方式 LBYL：問一下：我能拉你的手嗎？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這就是操作之前仔細檢查。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第二種方式 EAFP：直接先把手拉上，她要是甩開了再說其他的，要是沒拒絕就拉着唄。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這就是”事後獲取原諒比事前獲取許可更容易“，也就是先操作，遇到問題再處理。瞭解即可，不用特別去記憶。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"5.異常的好處","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們看一下，上述的兩種風格在處理代碼時究竟是怎樣的呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們先給一個特定的場景啊，處理王者榮耀遊戲開局時的異常代碼","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"LBYL 風格的代碼(不使用異常)","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d9/d922ffdf7c8e14684f375d89c767dc02.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"代碼的每一步執行完都要進行檢查，確認正確才能進行下一步。這就是在操作之前做檢查。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"EAFP 風格的代碼","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/52/52212e8d434256401fef0bc026fbd3b6.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在這裏我們能體會到Java 風格的代碼異常處理","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5e/5e283a4d8c777dbc4657cf341c7f1d36.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對比兩種不同風格的代碼，我們可以發現，使用第一種方式，正常流程和錯誤處理流程代碼混在一起，代碼整體顯得比較混亂。而第二種方式正常流程和錯誤流程是分離開的，更容易理解代碼。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"二、異常的基本語法","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"接下來，我們就正式開始了Java當中處理異常的基本語法講解了。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"1.基本格式","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"Java當中處理異常的基本格式","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/15/15c932dfdc6c32eb9699b96ed12fcafa.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"2. 是否處理異常對程序的影響","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看一組代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/64/64d7517b898d0501963c1b12a1464998.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這組代碼中，在代碼執行的第二步中，我們存在着數組越界異常，那麼第三步的 “hello” 是否會打印呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們運行程序，看結果","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/6d/6d87c94b0a57b8a1b30aee12c20b75a9.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"“hello” 並沒有打印，那麼這是爲什麼呢？此時程序出現異常了，而當程序出現異常時，那麼代碼將不會被執行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那麼我們還是想執行這個“hello”，那麼我們該怎麼辦呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們就將代碼寫成以下格式的代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/fa/fa1035682de0c88fd051e01a2f157058.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果:","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/47/4771a22c168b6e609643fed6b804d657.jpeg","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"hello 也成功進行了打印。也就是說，在這種方式下，代碼拋出異常，捕獲異常之後，代碼將繼續向後執行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那麼又有同學說了，我們定義的那個 e 沒有用到啊，我們再來看 e 的用處","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/21/213caa4e8816dd3988ca8d696decd90b.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"e.printStackTrace — 打印出現異常棧的追蹤","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看這時程序運行結果","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/47/47670162f3cfdabfcfb4e91b32a1a0aa.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這時就把出現異常的棧的位置打印出來了，這就是e的一個作用吧。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那麼又有同學來問了，爲什麼之前的 “hello”無法打印出來，之後的try…catch 捕捉異常之後能夠打印出來呢？","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/64/648fbe19c80e8becba472b4f71328c3a.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"3.用 try … catch 需要注意的問題","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1.在 catch 塊中，一定要捕獲相對應的異常，如果程序拋出的異常在catch 塊當中，不能被捕獲，那麼就會交給 JVM 處理。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"看以下代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/62/62b3dfe9504ebc2a68693b7d5c4ab712.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"在catch 塊當中並沒有捕獲到 數組越界異常，我們來看一下運行結果。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/fd/fdfcb9e985cf15d7f872f42ec128ce98.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"直接交給 JVM 處理，程序終止，不再向下執行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2.可以通過catch捕獲多個異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們可以在 try之後跟上多個 catch 來捕獲異常，如以下代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/88/886250adb6c0a9e6de3c6f5c5bd57857.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行程序結果如下：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/04/04ac3f30665ea508504e9a9cd6d15523.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們知道，所有的異常都繼承於Exception，那麼有人問了，我們可以直接捕獲一個Exception的異常嗎？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來試一下，我們知道捕捉異常的順序是按照代碼書寫的順序執行的，大家看一下這段代碼","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b4/b48066d1451efcd38caada815c23fbdc.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"當Exception 這個父類異常放在開頭，那麼下面的捕捉異常則進行報錯。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果這樣寫，那麼Exception後面所有的異常都失效了，爲什麼呢，因爲不管 try {} 裏面是什麼異常，都會在Exception 這一步進行捕獲到，後面的捕獲異常自然失效了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以當我們在前面寫了 Exception 這個捕獲異常時，後面就不要再進行捕獲其他異常了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那麼又有同學說了，我們爲了省事，那麼我們以後都捕獲 Exception 這個 異常不就好了？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當然不行，在這種情況下，我們不能區分我們捕獲到的是什麼異常。所以，不建議大家直接捕獲到一個 Exception 的異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3.不建議大家直接捕獲一個 Exception 的異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"有些同學想要省事，想要將兩個異常合併成一條進行捕捉，我們只需要將兩個異常用 | 進行連接即可。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"給個示例：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5c/5c86596389ae3e4aa5ddb348b1e3c887.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"看一下運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/50/502db431b2100e3109ce4c30bce8539e.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"成功運行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}},{"type":"strong","attrs":{}}],"text":"總結","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1.在 catch 塊中，一定要捕獲相對應的異常，如果程序拋出的異常在catch 塊當中，不能被捕獲，那麼就會交給 JVM 處理。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2.可以通過catch 捕獲多個異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3.不建議大家直接捕獲一個 Exception 的異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"4.可以用 | 同時處理兩個異常，如上例。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"4.關於異常的處理方式","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"異常的種類有很多，我們要根據不同的業務場景來決定。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對於比較嚴重的問題(例如和算錢相關的場景)，應該讓程序直接崩潰，防止造成更嚴重的後果。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對於不太嚴重的問題(大多數場景)，可以記錄錯誤日誌，並通過監控報警程序及時通知程序猿。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對於可能會恢復的問題(和網絡相關的場景)，可以嘗試進行重試。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在我們當前的代碼中採取的是經過簡化的第二種方式，我們記錄的錯誤日誌是出現異常的方法調用信息，能很快速地讓我們找到出現異常的位置，以後在實際工作中我們會採取更完備的方式來記錄異常信息。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"關於 “調用棧”","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"方法之間是存在相互調用關係的，這種調用關係我們可以用 “調用棧” 來描述。在 JVM 中有一塊內存空間稱爲 “虛擬機棧” 專門存儲方法之間的調用關係，當代碼中出現異常的時候，我們就可以使用 e.printStackTrace(); 的方式查看出現異常代碼的調用棧。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"5.finally 的使用","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們再來看一下異常基礎語法的學習","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/8a/8ac244a0cb66bc70995cfcba1cdefde0.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們看到了try…catch 之後還可以跟着 finally","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那我們來說一下 finally 的特性","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"不管 這個代碼 是否拋出異常，finally 的 內容都會被執行。所以 finally 經常來做一些善後的內容。比如：關閉資源","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看一下這一組代碼","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ef/efb1f2c22f5adc08f7ec2ca23a3f23d7.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"考一下大家，這組代碼執行的結果是什麼呢?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果如下：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d1/d1e5925df850d40986428e91ab461c26.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"打印結果爲2，這是爲什麼呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首先我們需要明確的一點是，finally 的內容一定會被執行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們分析一下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在try 塊當中，在打印 array[4]時出現異常，後面的return 語句就不再執行了，所以最後執行 finally 塊，返回2.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們再來看一個代碼示例：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/a3/a30f1fbaf19f4f6c33b0662fa67c03b0.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這組代碼執行的結果是什麼呢?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/44/44c19bcf76f06576516f33312d2835cf.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"最後返回了2。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這又再次明確了一點：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"finally 的內容是一定會被執行的","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"finally 的使用 總結：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1.finally 塊當中的代碼終究會被執行的","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2 .不建議在 finally 當中出現 return 語句.","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"6.異常處理流程","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/9e/9e4f73a847b24a71020d4a8953568415.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"好了，到現在，我們算是講清楚了 try…catch…finally 及異常處理的流程等問題，那麼大家以後在寫代碼的過程中，一定要記得去使用 try…catch，不能一味地交給 JVM 來處理它，好了我們開始下一塊內容——拋出異常。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"7.拋出異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"除了 Java 內置的類會拋出一些異常之外，程序猿也可以手動拋出某個異常。使用 throw 關鍵字完成這個操作。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"throw 一般拋出一個你想要拋出的異常（或者自定義的異常）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（1）throw 的使用","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看代碼示例：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/05/051f4cebbbf145630d7950bdf496271f.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們用 throw new 了一個算數異常，爲什麼要 new 呢？ 因爲算數異常本身也是一個類，也要實例化。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看運行時結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b9/b9c3d6227810016a609a7239a1fca43c.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"成功地拋出異常了，但是這樣寫有一個不好的地方。我們拋出了一個異常但是呢，這個異常我們只是拋出了但是並未處理，所以最後程序出現異常後交給JVM處理，程序最後終止。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（2）聲明異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"對於我們調用devide 方法的人來說啊，如果 devide 方法的內容很多，我們就看不出 devide 會拋出一個異常。那麼爲了讓調用devide 方法的人知道，我們調用這個方法會拋出這個異常，一般情況下，我們會給這個方法進行聲明異常。那麼怎麼聲明呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通過throws 聲明這個方法會拋出一個異常","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"下面我們來看代碼示例：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d0/d0afd1f7f7c60b267227f54a76194bfc.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"方法調用者知道了調用該方法可能會拋出 算數異常，就用上了 try…catch 來捕獲異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/04/0447d7e3f5cdce1bdeef5fb5f78c61a8.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（3）小結","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2b/2bad90283f2a362ddb65c0f1e261065d.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"三、Java異常體系","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那麼異常到底有多少種？要了解這個問題，我們就需要知道Java的異常體系了。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/cd/cdbb40920e610ce001e46893c65a1a89.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上圖並沒有將所有的異常都列舉出來，只是大概演示一下。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在Java當中，我們所看到的異常，其實也就是對應着一個類。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"由上圖中我們可以看到，整個Java 異常體系都是繼承於頂層類 Throwable，那麼 Throwable 就是所有異常、錯誤的父類。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"對於Throwable 來說，直接繼承這個類的有兩個子類，","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Error ( 錯誤 ) 和 Exception（異常）。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看一下 jdk_api 幫助手冊中對 Throwable 的解釋","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d8/d89d96dd361a29249e2d180d4e2a28e3.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們這篇講的是異常，怎麼又出現一個錯誤Error呢?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們也來認識以下Error，比如說我們寫一個代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/99/995e97c525b437f3fc7f1ae746b0f448.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行之後出現以下結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/bf/bf5ef438e7d618e5c0e557839be1344d.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來對比一下：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/e6/e642e79e0cf6b4b663af1f40a3b0b20b.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"異常是以Exception 結尾的，而錯誤是以 Error 結尾的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"對於Error 來說——這種錯誤一定得由程序員自己解決。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"而對於Exception 來說——異常時可以由程序自己解決的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"而異常又有以下劃分","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c2/c2bbc63bb7421f1e6a0dfa162a5ea83d.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行時異常 Runtime Exception就是我們上面提到的算數異常、數組越界異常、類型轉換異常等等，那麼就有同學問了？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"什麼是運行時異常？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"運行時異常就是在程序運行的時候拋出的異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"什麼是編譯時異常？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"編譯時異常就是在程序編譯時拋出的異常。如果一段代碼可能拋出受查異常，那麼必須顯式進行處理。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"顯式處理的方式有兩種：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"a) 使用 try catch 包裹起來；","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"b) 在方法上加上異常說明，相當於將處理動作交給上級調用者。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"別忘了 IDEA 神奇的 alt + enter，能夠快速修正代碼。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}},{"type":"strong","attrs":{}}],"text":"小結","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ef/ef310c72b656ca374ebaa52d4d52aa79.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"四、自定義異常類","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"Java 中雖然已經內置了豐富的異常類，但是我們實際場景中可能還有一些情況需要我們對異常類進行擴展，創建符合我們實際情況的異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來實現一個簡單的自定義的異常類","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"首先我們要自定義一個異常類，同時繼承一個父類異常。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c0/c0b75b8005839934898871400d52ed1d.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那麼這個我們自定義的異常怎麼用呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"下面我們來看","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/20/203be5191fcb372fbb62fe214ed1cd81.jpeg","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c4/c49165da40e45f521ad15d6e785ab128.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這就是我們自定義異常的使用。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們再來一個代碼示例，下面我們給一個真實的業務場景。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"例如，我們實現一個用戶登陸功能。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/86/86ccaef0050f394b8aed833741f6d2ac.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"此時我們在處理用戶名密碼錯誤的時候可能就需要拋出兩種異常，我們可以基於已有的異常類進行擴展(繼承)，創建和我們業務相關的異常類。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/7a/7ac4322b8cec62be9a798127d661396b.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"此時我們的 login 代碼可以改成","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f4/f402f339f0d53cff77c0919b618bc53f.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"自定義類的注意事項：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1.自定義異常通常會繼承自 Exception 或者 RuntimeException","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2.繼承自 Exception 的異常默認是受查異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3.繼承自 RuntimeException 的異常默認是非受查異常.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#1F1F1F","name":"user"}}],"text":"今日份分享已結束，請大家多多包涵和指點！","attrs":{}}]}]}
夯實基礎，美團大佬帶你深入理解Java中的異常體系，再也不踩坑了
{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#1F1F1F","name":"user"}}],"text":"今日分享開始啦，請大家多多指教~","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"一、初識異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"經常有同學看到異常來問了，異常到底是什麼？ 而在我們之前的學習中，我們其實已經接觸到了Java當中的異常。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"1.算數異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首先我們遇到的第一個異常是我們在講除號運算符時遇到的——算數異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"見以下代碼","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/1f/1f8d47d282c6ef7f2d82f18733444716.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們在分子的位置出現了0，來運行以上代碼。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ac/ac060dccfff8e8751fd2ba837a0a114e.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"2.數組下標越界異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在數組篇我們也提到了數組越界的問題","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看以下代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f0/f0ea7620deebee4dfa6e72040988e315.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行時結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/db/db6bd333784ecf144810fc347dbca082.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"查看異常的信息","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/78/781acba2a0e534bd7be72bd1c74c2e79.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"3.空指針異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"空指針異常也在之前的學習中經常出現","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"看以下代碼","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/da/da3f8346ede29b8d6fef6f30713f96ca.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們將 array 數組置爲 null ，之後再去訪問這個數組，就出現了空指針異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/50/50f5f6ce2e283e5b84b168dab7c172c7.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這些異常都是需要我們在平時所積累出來的，所謂異常指的就是程序在運行時出現錯誤時通知調用者的一種機制。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"關鍵字 “運行時”","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"有些錯誤是這樣的，例如將 System.out.println 拼寫錯了，寫成了 system.out.println. 此時編譯過程中就會出錯，這是 “編譯期” 出錯。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"而運行時指的是程序已經編譯通過得到 class 文件了，再由 JVM 執行過程中出現的錯誤。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"4.異常的處理方式","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"異常的種類有很多，不同種類的異常具有不同的含義，也有不同的處理方式。（在此瞭解即可）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}},{"type":"strong","attrs":{}}],"text":"防禦式編程","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"錯誤在代碼中是客觀存在的，因此我們要讓程序出現問題的時候及時通知程序猿，我們有兩種主要的方式。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"LBYL: Look Before You Leap.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在操作之前就做充分的檢查。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"EAFP: It’s Easier to Ask Forgiveness than Permission.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"“事後獲取原諒比事前獲取許可更容易”，也就是先操作，遇到問題再處理。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"其實很好理解，打一個非常形象的比喻來理解啊：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"比如說有一個你非常喜歡的女生，你想要去拉她的手，那麼有幾種方式呢?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第一種方式 LBYL：問一下：我能拉你的手嗎？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這就是操作之前仔細檢查。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"第二種方式 EAFP：直接先把手拉上，她要是甩開了再說其他的，要是沒拒絕就拉着唄。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這就是”事後獲取原諒比事前獲取許可更容易“，也就是先操作，遇到問題再處理。瞭解即可，不用特別去記憶。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"5.異常的好處","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們看一下，上述的兩種風格在處理代碼時究竟是怎樣的呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們先給一個特定的場景啊，處理王者榮耀遊戲開局時的異常代碼","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"LBYL 風格的代碼(不使用異常)","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d9/d922ffdf7c8e14684f375d89c767dc02.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"代碼的每一步執行完都要進行檢查，確認正確才能進行下一步。這就是在操作之前做檢查。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"EAFP 風格的代碼","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/52/52212e8d434256401fef0bc026fbd3b6.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在這裏我們能體會到Java 風格的代碼異常處理","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5e/5e283a4d8c777dbc4657cf341c7f1d36.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對比兩種不同風格的代碼，我們可以發現，使用第一種方式，正常流程和錯誤處理流程代碼混在一起，代碼整體顯得比較混亂。而第二種方式正常流程和錯誤流程是分離開的，更容易理解代碼。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"二、異常的基本語法","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"接下來，我們就正式開始了Java當中處理異常的基本語法講解了。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"1.基本格式","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"Java當中處理異常的基本格式","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/15/15c932dfdc6c32eb9699b96ed12fcafa.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"2. 是否處理異常對程序的影響","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看一組代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/64/64d7517b898d0501963c1b12a1464998.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這組代碼中，在代碼執行的第二步中，我們存在着數組越界異常，那麼第三步的 “hello” 是否會打印呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們運行程序，看結果","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/6d/6d87c94b0a57b8a1b30aee12c20b75a9.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"“hello” 並沒有打印，那麼這是爲什麼呢？此時程序出現異常了，而當程序出現異常時，那麼代碼將不會被執行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那麼我們還是想執行這個“hello”，那麼我們該怎麼辦呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們就將代碼寫成以下格式的代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/fa/fa1035682de0c88fd051e01a2f157058.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果:","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/47/4771a22c168b6e609643fed6b804d657.jpeg","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"hello 也成功進行了打印。也就是說，在這種方式下，代碼拋出異常，捕獲異常之後，代碼將繼續向後執行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那麼又有同學說了，我們定義的那個 e 沒有用到啊，我們再來看 e 的用處","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/21/213caa4e8816dd3988ca8d696decd90b.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"e.printStackTrace — 打印出現異常棧的追蹤","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看這時程序運行結果","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/47/47670162f3cfdabfcfb4e91b32a1a0aa.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這時就把出現異常的棧的位置打印出來了，這就是e的一個作用吧。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那麼又有同學來問了，爲什麼之前的 “hello”無法打印出來，之後的try…catch 捕捉異常之後能夠打印出來呢？","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/64/648fbe19c80e8becba472b4f71328c3a.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"3.用 try … catch 需要注意的問題","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1.在 catch 塊中，一定要捕獲相對應的異常，如果程序拋出的異常在catch 塊當中，不能被捕獲，那麼就會交給 JVM 處理。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"看以下代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/62/62b3dfe9504ebc2a68693b7d5c4ab712.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"在catch 塊當中並沒有捕獲到 數組越界異常，我們來看一下運行結果。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/fd/fdfcb9e985cf15d7f872f42ec128ce98.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"直接交給 JVM 處理，程序終止，不再向下執行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2.可以通過catch捕獲多個異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們可以在 try之後跟上多個 catch 來捕獲異常，如以下代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/88/886250adb6c0a9e6de3c6f5c5bd57857.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行程序結果如下：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/04/04ac3f30665ea508504e9a9cd6d15523.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們知道，所有的異常都繼承於Exception，那麼有人問了，我們可以直接捕獲一個Exception的異常嗎？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來試一下，我們知道捕捉異常的順序是按照代碼書寫的順序執行的，大家看一下這段代碼","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b4/b48066d1451efcd38caada815c23fbdc.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"當Exception 這個父類異常放在開頭，那麼下面的捕捉異常則進行報錯。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果這樣寫，那麼Exception後面所有的異常都失效了，爲什麼呢，因爲不管 try {} 裏面是什麼異常，都會在Exception 這一步進行捕獲到，後面的捕獲異常自然失效了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以當我們在前面寫了 Exception 這個捕獲異常時，後面就不要再進行捕獲其他異常了。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"那麼又有同學說了，我們爲了省事，那麼我們以後都捕獲 Exception 這個 異常不就好了？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當然不行，在這種情況下，我們不能區分我們捕獲到的是什麼異常。所以，不建議大家直接捕獲到一個 Exception 的異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3.不建議大家直接捕獲一個 Exception 的異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"有些同學想要省事，想要將兩個異常合併成一條進行捕捉，我們只需要將兩個異常用 | 進行連接即可。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"給個示例：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/5c/5c86596389ae3e4aa5ddb348b1e3c887.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"看一下運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/50/502db431b2100e3109ce4c30bce8539e.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"成功運行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}},{"type":"strong","attrs":{}}],"text":"總結","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1.在 catch 塊中，一定要捕獲相對應的異常，如果程序拋出的異常在catch 塊當中，不能被捕獲，那麼就會交給 JVM 處理。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2.可以通過catch 捕獲多個異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3.不建議大家直接捕獲一個 Exception 的異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"4.可以用 | 同時處理兩個異常，如上例。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"4.關於異常的處理方式","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"異常的種類有很多，我們要根據不同的業務場景來決定。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對於比較嚴重的問題(例如和算錢相關的場景)，應該讓程序直接崩潰，防止造成更嚴重的後果。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對於不太嚴重的問題(大多數場景)，可以記錄錯誤日誌，並通過監控報警程序及時通知程序猿。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對於可能會恢復的問題(和網絡相關的場景)，可以嘗試進行重試。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在我們當前的代碼中採取的是經過簡化的第二種方式，我們記錄的錯誤日誌是出現異常的方法調用信息，能很快速地讓我們找到出現異常的位置，以後在實際工作中我們會採取更完備的方式來記錄異常信息。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"關於 “調用棧”","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"方法之間是存在相互調用關係的，這種調用關係我們可以用 “調用棧” 來描述。在 JVM 中有一塊內存空間稱爲 “虛擬機棧” 專門存儲方法之間的調用關係，當代碼中出現異常的時候，我們就可以使用 e.printStackTrace(); 的方式查看出現異常代碼的調用棧。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"5.finally 的使用","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們再來看一下異常基礎語法的學習","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/8a/8ac244a0cb66bc70995cfcba1cdefde0.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們看到了try…catch 之後還可以跟着 finally","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那我們來說一下 finally 的特性","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"不管 這個代碼 是否拋出異常，finally 的 內容都會被執行。所以 finally 經常來做一些善後的內容。比如：關閉資源","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看一下這一組代碼","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ef/efb1f2c22f5adc08f7ec2ca23a3f23d7.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"考一下大家，這組代碼執行的結果是什麼呢?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果如下：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d1/d1e5925df850d40986428e91ab461c26.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"打印結果爲2，這是爲什麼呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"首先我們需要明確的一點是，finally 的內容一定會被執行。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們分析一下：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在try 塊當中，在打印 array[4]時出現異常，後面的return 語句就不再執行了，所以最後執行 finally 塊，返回2.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們再來看一個代碼示例：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/a3/a30f1fbaf19f4f6c33b0662fa67c03b0.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這組代碼執行的結果是什麼呢?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/44/44c19bcf76f06576516f33312d2835cf.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"最後返回了2。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這又再次明確了一點：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"finally 的內容是一定會被執行的","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"finally 的使用 總結：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1.finally 塊當中的代碼終究會被執行的","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2 .不建議在 finally 當中出現 return 語句.","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"6.異常處理流程","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/9e/9e4f73a847b24a71020d4a8953568415.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"好了，到現在，我們算是講清楚了 try…catch…finally 及異常處理的流程等問題，那麼大家以後在寫代碼的過程中，一定要記得去使用 try…catch，不能一味地交給 JVM 來處理它，好了我們開始下一塊內容——拋出異常。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"7.拋出異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"除了 Java 內置的類會拋出一些異常之外，程序猿也可以手動拋出某個異常。使用 throw 關鍵字完成這個操作。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"throw 一般拋出一個你想要拋出的異常（或者自定義的異常）","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（1）throw 的使用","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看代碼示例：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/05/051f4cebbbf145630d7950bdf496271f.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們用 throw new 了一個算數異常，爲什麼要 new 呢？ 因爲算數異常本身也是一個類，也要實例化。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看運行時結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/b9/b9c3d6227810016a609a7239a1fca43c.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"成功地拋出異常了，但是這樣寫有一個不好的地方。我們拋出了一個異常但是呢，這個異常我們只是拋出了但是並未處理，所以最後程序出現異常後交給JVM處理，程序最後終止。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（2）聲明異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"對於我們調用devide 方法的人來說啊，如果 devide 方法的內容很多，我們就看不出 devide 會拋出一個異常。那麼爲了讓調用devide 方法的人知道，我們調用這個方法會拋出這個異常，一般情況下，我們會給這個方法進行聲明異常。那麼怎麼聲明呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"通過throws 聲明這個方法會拋出一個異常","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"下面我們來看代碼示例：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d0/d0afd1f7f7c60b267227f54a76194bfc.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"方法調用者知道了調用該方法可能會拋出 算數異常，就用上了 try…catch 來捕獲異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/04/0447d7e3f5cdce1bdeef5fb5f78c61a8.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（3）小結","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/2b/2bad90283f2a362ddb65c0f1e261065d.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"三、Java異常體系","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那麼異常到底有多少種？要了解這個問題，我們就需要知道Java的異常體系了。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/cd/cdbb40920e610ce001e46893c65a1a89.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上圖並沒有將所有的異常都列舉出來，只是大概演示一下。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在Java當中，我們所看到的異常，其實也就是對應着一個類。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"由上圖中我們可以看到，整個Java 異常體系都是繼承於頂層類 Throwable，那麼 Throwable 就是所有異常、錯誤的父類。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"對於Throwable 來說，直接繼承這個類的有兩個子類，","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Error ( 錯誤 ) 和 Exception（異常）。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來看一下 jdk_api 幫助手冊中對 Throwable 的解釋","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/d8/d89d96dd361a29249e2d180d4e2a28e3.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們這篇講的是異常，怎麼又出現一個錯誤Error呢?","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們也來認識以下Error，比如說我們寫一個代碼：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/99/995e97c525b437f3fc7f1ae746b0f448.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行之後出現以下結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/bf/bf5ef438e7d618e5c0e557839be1344d.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來對比一下：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/e6/e642e79e0cf6b4b663af1f40a3b0b20b.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"異常是以Exception 結尾的，而錯誤是以 Error 結尾的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"對於Error 來說——這種錯誤一定得由程序員自己解決。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"而對於Exception 來說——異常時可以由程序自己解決的。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"而異常又有以下劃分","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c2/c2bbc63bb7421f1e6a0dfa162a5ea83d.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行時異常 Runtime Exception就是我們上面提到的算數異常、數組越界異常、類型轉換異常等等，那麼就有同學問了？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"什麼是運行時異常？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"運行時異常就是在程序運行的時候拋出的異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"什麼是編譯時異常？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"編譯時異常就是在程序編譯時拋出的異常。如果一段代碼可能拋出受查異常，那麼必須顯式進行處理。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"顯式處理的方式有兩種：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"a) 使用 try catch 包裹起來；","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"b) 在方法上加上異常說明，相當於將處理動作交給上級調用者。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"別忘了 IDEA 神奇的 alt + enter，能夠快速修正代碼。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}},{"type":"strong","attrs":{}}],"text":"小結","attrs":{}},{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/ef/ef310c72b656ca374ebaa52d4d52aa79.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"四、自定義異常類","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"Java 中雖然已經內置了豐富的異常類，但是我們實際場景中可能還有一些情況需要我們對異常類進行擴展，創建符合我們實際情況的異常。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們來實現一個簡單的自定義的異常類","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"首先我們要自定義一個異常類，同時繼承一個父類異常。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c0/c0b75b8005839934898871400d52ed1d.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"那麼這個我們自定義的異常怎麼用呢？","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"下面我們來看","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/20/203be5191fcb372fbb62fe214ed1cd81.jpeg","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"運行結果：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/c4/c49165da40e45f521ad15d6e785ab128.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"這就是我們自定義異常的使用。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"我們再來一個代碼示例，下面我們給一個真實的業務場景。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"例如，我們實現一個用戶登陸功能。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/86/86ccaef0050f394b8aed833741f6d2ac.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"此時我們在處理用戶名密碼錯誤的時候可能就需要拋出兩種異常，我們可以基於已有的異常類進行擴展(繼承)，創建和我們業務相關的異常類。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/7a/7ac4322b8cec62be9a798127d661396b.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"此時我們的 login 代碼可以改成","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f4/f402f339f0d53cff77c0919b618bc53f.png","alt":null,"title":null,"style":[{"key":"width","value":"75%"},{"key":"bordertype","value":"none"}],"href":null,"fromPaste":true,"pastePass":true}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"自定義類的注意事項：","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1.自定義異常通常會繼承自 Exception 或者 RuntimeException","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2.繼承自 Exception 的異常默認是受查異常","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3.繼承自 RuntimeException 的異常默認是非受查異常.","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#1F1F1F","name":"user"}}],"text":"今日份分享已結束，請大家多多包涵和指點！","attrs":{}}]}]}
發表評論
所有評論
還沒有人評論，想成為第一個評論的人麼? 請在上方評論欄輸入並且點擊發布.
相關文章