如何理解Java8 的函數式編程

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Java8 出現的時間已經不算短了，免費維護期馬上也要到期了，官方已經開始推薦使用 Java11。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Java8 是革命性的一個版本，一直以來，Java 最受詬病的地方就是代碼寫起來很囉嗦，僅僅寫一個 HelloWorld 都需要些很多的樣板代碼。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在 Java8 推出之後，囉嗦的代碼有了很大的改觀，Java 也可以寫出簡單優美的代碼。最明顯的改觀就是 Java 開始支持函數式編程。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"函數式編程的定義很晦澀，但是我們可以將函數式編程理解爲函數本身可以作爲參數進行傳遞，就是說，參數不僅僅可以是數據，也可以是行爲（函數或者方法的實現其實就是邏輯行爲）。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可能是 Java8 步子跨的太大，以至於現在還有很多人沒有趕上來，依然用 Java8 在寫 Java5 風格的代碼。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這篇文章的目的就是徹底說清楚 Java8 的變化，以及快速全面的使用 Java8 的特性，讓 Java 代碼優雅起來。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"函數式接口"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在開始說 Java8 的函數式編程之前，我們需要說明一下，在 Java8 中新增加的一個概念，叫"},{"type":"text","marks":[{"type":"strong"}],"text":"函數式接口"},{"type":"text","text":"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這個函數式接口是 Java8 實現函數式編程的基礎，正是這類接口的存在，才能把函數（方法）當做參數進行傳遞，至少表面上看起來是這樣的，但是實際上傳遞的還是對象，這個問題我們下面再討論，先回到函數式接口。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面就是一個函數式接口："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"public interface Action {\n public void action();\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這個函數式看起來和普通的接口沒有什麼區別，唯一的區別是函數式接口只能有"},{"type":"text","marks":[{"type":"strong"}],"text":"一個抽象方法"},{"type":"text","text":"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果你想讓別人立馬理解這個接口是函數式接口，可以加上 "},{"type":"codeinline","content":[{"type":"text","text":"@FunctionalInterface"}]},{"type":"text","text":" 註解，這個註解不會提供任何額外的功能，僅僅用來表示這個接口是一個函數式接口。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"@FunctionalInterface\npublic interface Action {\n public void action();\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"只能有一個抽象方法是爲了更方便的把函數作爲參數來傳遞，這個後面再細說。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"我們可以根據自己的需要來定義函數式接口，JDK 爲了使用方便，內置了很多函數式接口，日常使用完全夠了。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"常用的函數接口有："}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Function"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Predicate"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Consumer"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"函數式接口其實就這麼簡單，看到這裏你可能還是對函數式接口不是很理解，沒關係，現在你僅僅只需要記住"},{"type":"text","marks":[{"type":"strong"}],"text":"函數式接口就是模板"},{"type":"text","text":"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"Lambda 表達式"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"說起 Java8 的函數式編程，很多人都知道 lambda 表達式，這也是 Java8 中最容易被人記住的地方。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"先來通過一個直觀的例子來了解一下 lambda，在操作 ArrayList 等數據結構時，我們有可能要對其中的數據進行排序，比如："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Comparator comparator = new Comparator() {\n public int compare(Integer i1, Integer i2) {\n return i1.comparaTo(i2);\n }\n};"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在上面的代碼中，真正有用的代碼也有比較大小的那行，其他的都是樣板代碼。在這樣的情況下，lambda 就很有用。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Comparator comparator = (Integer i1, Integer i2) -> {return i1.compareTo(i2);}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這樣看起來是不是很簡單了，但是還是繼續優化，可以把返回參數的部分也省略："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Comparator comparator = (Integer i1, Integer i2) -> i1.compareTo(i2)"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"既然兩個參數都是 Integer 那是不是也可以省略，最後就得到了下面這樣的形式："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Comparator comparator = (i1, i2) -> i1.compareTo(i2)"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這就是 lambda 的力量，可以把上面那麼多的代碼濃縮成一行。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"lambda 其實就是一段代碼，但也不僅僅是一段代碼，再簡單的 lambda 也會有三部分，參數列表，箭頭和 lambda 主體，上面的 "},{"type":"codeinline","content":[{"type":"text","text":"(i1, i2)"}]},{"type":"text","text":" 就是參數列表， "},{"type":"codeinline","content":[{"type":"text","text":"i1.compareTo(i2)"}]},{"type":"text","text":" 就是 lambda 主體，箭頭把這兩部分隔開了。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"lambda 是匿名的，這點和 Java 中的匿名實現類有點像（本質上一樣），而且它是一種函數，不屬於任何類（屬於類的函數稱之爲方法），並且可以作爲參數進行傳遞，而且還很簡潔。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"看到這裏，可能就有人猜到函數式接口和 lambda 之間可能有某些關係了，沒錯，我們已經快說到最重要的部分。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在這之前再來理解一個概念，函數簽名，函數簽名爲可以表示一類函數，如果兩個函數的以下部分相同，就可以說這兩個函數的簽名一致："}]},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"函數參數及其類型"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"返回值及其類型"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"可能會拋出的異常"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"還有訪問控制符（public等等）"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"最關鍵的地方來了，"},{"type":"text","marks":[{"type":"strong"}],"text":"只要 lambda 和函數式接口方法的簽名一致，lambda 表達式就可以作爲參數傳入到以該函數式接口爲參數類型的方法中"},{"type":"text","text":"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"來看個詳細的例子， "},{"type":"codeinline","content":[{"type":"text","text":"Comparator"}]},{"type":"text","text":" 接口的定義如下："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"@FunctionalInterface\npublic interface Comparator {\n int compare(T o1, T o2);\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"雖然 Comparator 中方法不止一個，但是抽象方法只有 "},{"type":"codeinline","content":[{"type":"text","text":"compare"}]},{"type":"text","text":" 一個，上面的 lambda 完全可以作爲 compare 方法的實現，實際上，"},{"type":"text","marks":[{"type":"strong"}],"text":"lambda 表達式確實是作爲函數式接口抽象方法的實現，而且，lambda 表達式爲作爲整個函數接口的實例"},{"type":"text","text":"。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"到這裏，真相大白，Java 8 的雖然支持了函數式編程，這不代表函數就是 Java中的一等公民了，每一個函數其實還是被包裹成一個對象，對象依然是 Java 中的一等公民。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"所以簡單來說，只要 lambda 的表達式的參數和返回類型可以與函數式接口中的抽象方法對的上，lambda 就可以作爲該函數式接口的實現進行傳遞。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"比如上面列舉的幾種函數式接口，其實就是對一些通用函數的抽象，比如 Function 函數式接口如下："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"@FunctionalInterface\npublic interface Function {\n R apply(T t);\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這種就代表接受一個參數，返回另一個值的函數，只要滿足這個要求的 lambda 表達式都可以作爲 它的實現。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"再比如 Predicate 接口，代表接受一個參數返回一個布爾值的函數："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"@FunctionalInterface\npublic interface Predicate {\n boolean test(T t);\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Comsumer 接口表示接受一個參數，什麼都不返回的函數："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"@FunctionalInterface\npublic interface Predicate {\n boolean test(T t);\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果這樣理解起來還是有點困難，那就把這些函數式接口理解爲 lambda 表達式的類型。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"類型檢查和類型推斷"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在上面我們說到了只要函數式接口抽象方法的函數簽名與 lambda 一致，那麼就可以把 lambda 表達式作爲該函數式接口的實現。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"上面的例子中， lambda 的參數類型也是可以省略的，那麼 Java 是如何判斷 lambda 是否與函數式接口匹配呢？"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"如果 lambda 表達式中，參數和返回值的類型都省略之後，需要從使用 lambda 的上下文推斷出來。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"link","attrs":{"href":"03-08-87-%E5%A6%82%E4%BD%95%E7%BC%96%E5%86%99Java8%20%E9%A3%8E%E6%A0%BC%E7%9A%84%E4%BB%A3%E7%A0%81%2059c60dc717f240719b4fdb4382b8b74a/Untitled.png","title":null},"marks":[{"type":"underline"}]}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/15/157cfb9f21779fc8c9c0e5c418bef203.png","alt":null,"title":"","style":[{"key":"width","value":"100%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"方法引用"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本來到這裏應該就很完美了，lambda 夠簡潔，用它寫代碼，可以省略很多無用的樣本代碼，但是 lambda 也不完美，因爲 lambda 表達式的代碼很難複用，而且很多的 lambda 表達式僅僅就是調用了其他的方法。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這個時候，方法引用就可以派上用場了，比如上面的例子，其實僅僅就是調用了 "},{"type":"codeinline","content":[{"type":"text","text":"Integer.compareTo()"}]},{"type":"text","text":" 方法："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Comparator comparator = (i1, i2) -> i1.compareTo(i2)"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"還可以簡化成下面的樣子："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"Comparator comparator = Integer::compareTo"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"使用方法引用的時候，要使用 "},{"type":"codeinline","content":[{"type":"text","text":"::"}]},{"type":"text","text":" ，而且任何方法都可以這樣被引用，無論是靜態方法還是實例方法。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"方法引用可以被認爲是 lambda 的語法糖，使用方法引用可以讓代碼更加簡潔，更直觀，看到方法引用的名稱就能大概知道代碼的邏輯，並且還可以對一些代碼進行復用。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":2},"content":[{"type":"text","text":"寫出Java8 風格的代碼"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在 Java8 之後，很多代碼的寫法應該摒棄，下面列舉一些常見的例子。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"遍歷 List"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Java8 以前："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"for(Integer i : list) {\n System.out.println(i);\n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Java8 及以後："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"list.forEach(System.out::println);"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"forEach 接收 Consumer 類型的函數，而 System.out.println() 剛好就符合要求。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"遍歷 Map"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Java8 以前："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"for (Map.Entry entry : map.entrySet()) {\n \n System.out.println(\"Key: \" + entry.getKey() + \", Value:\" + entry.getValue());\n \n}"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Java8 及以後："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"map.forEach((k, v) -> {System.out.println(\"Key: \"+ k +\", Value: \"+ v)});"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這裏的 forEach 不是接收 Consumer 類型的函數，而是接收 BiConsumer 類的函數，可以用來處理 map 這種包含 key-value 類型的數據，在大多數場景下，內置的函數式接口以及足夠我們使用，只有在一些特殊的場景下才需要自己定製。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"這裏也沒有現成的方法引用，所以就可以使用 lambda 表達式來實現。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":3},"content":[{"type":"text","text":"執行異步任務"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"假如要使用線程池來執行任務。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Java8 以前："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"ThreadPoolExecutor executor = new ThreadPoolExecutor(10, 10, 0, TimeUnit.SECONDS, new ArrayBlockingQueue(2000));\n\nexecutor.submit(new Runnable() {\n public void run() {\n System.out.println(\"Thread pool execute\");\n }\n}); "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Java8 以後："}]},{"type":"codeblock","attrs":{"lang":null},"content":[{"type":"text","text":"ThreadPoolExecutor executor = new ThreadPoolExecutor(10, 10, 0, TimeUnit.SECONDS, new ArrayBlockingQueue(2000));\n\nexecutor.submit(() ->{\n System.out.println(\"Thread pool execute\");\n});"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"也可以使用 lambda 來解決這個問題，Runnable 也是一個函數式接口。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#F5222D","name":"red"}}],"text":"文 / Rayjun"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"本文首發於公衆號 Rayjun"}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/af/aff0781fde8a41d0b23e298cc79993c7.jpeg?x-oss-process=image/resize,p_80/auto-orient,1","alt":null,"title":"","style":[{"key":"width","value":"25%"},{"key":"bordertype","value":"none"}],"href":"","fromPaste":false,"pastePass":false}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}