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強推！阿里p7大佬整理的這幾款高效Java工具，網友：再也不加班了
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name)","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"該方法用來根據環境變量的名字獲取環境變量。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（3）gc()","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"java垃圾回收器，這個方法不需要我們去調用，jvm發現系統有未使用的對象，會自己進行執行。通常會有兩種情況下會調用gc：當jvm內存不足時會調用；當cpu空閒的時候調用。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"（4）exit(int status)","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"退出虛擬機。exit(int)方法是終止當前正在運行的java虛擬機，參數是狀態碼。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"①該方法用於退出jvm，如果參數是0表示正常退出jvm，非0表示異常退出jvm。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"②退出jvm後，後面的代碼就不會執行。無論傳0還是傳1，Jvm都會退出。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"③注意：0或者非0的數據都可以退出Jvm，對於用戶而言沒有任何區別，對於windows是有作用的，因爲如果傳非0對於windows而言是異常終止的，如果是正版的操作系統，對於異常退出的軟件，需要把這些異常退出的軟件信息做成報告發送給微軟，微軟就可以針對這些問題對系統做出一些修改。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"④我們程序員的編程習慣是：如果在try塊中退出Jvm，try塊裏面是沒有異常的代碼，所以try塊中要傳0，如果是在catch塊裏面退出Jvm，我們習慣於用非0退出。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"三、Number 類","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"數據的基本數據類型有byte、int、short、long、double、float、boolean、char 等8種。但在實際的開發當中，我們有時候會遇到需要使用數字對象，而不是數據類型的情況。爲解決這個問題，java爲每一種數據類型，提供了相對應的類，即包裝類，對應的包裝類型也有八種：Byte、Integer、Short、Long、Double、Float、Boolean、Character。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"包裝類型都是用final聲明，不可以被繼承重寫。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"當數據類型需要被當做對象使用時，編譯器會將數據類型轉換爲對應的包裝類，這個過程被稱爲裝箱；而當包裝類對象被當做數據類型使用時，編譯器會將包裝類轉換爲對應的數據類型，這個過程被稱爲拆箱。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Number類是java.lang包下的一個抽象類，提供了將包裝類型拆箱成基本類型的方法，所有基本數據類型（除 boolean 和 char）的包裝類型都繼承了該抽象類，並且是final聲明不可繼承改變。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/81/814a25f391bcf4998f1ff8f354975b0d.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","text":"Number 的常用方法","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/3e/3e24ea585be8dff99fed2d97ab2db8f9.jpeg","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、格式化","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Format 是一個用於格式化語言環境敏感的信息（如日期、消息和數字）的抽象基類。Format 定義了編程接口，用於將語言環境敏感的對象格式化爲 String（使用 format 方法）和將 String 重新解析爲對象（使用 parseObject 方法）。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/a8/a8e89b56963e3183a5cc8a7201f30252.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":"Java 平臺爲格式化日期、消息和數字分別提供了三個特殊的 Format 的子類：DateFormat、MessageFormat 和 NumberFormat。具體的子類必須實現三個方法：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/1b/1b41b9a2e943a3b151efcb28423cd53b.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":"1、DateFormat","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"DateFormat 是日期/時間格式化子類的抽象類，它以與語言無關的方式格式化並解析日期或時間。 SimpleDateFormat 是一個以與語言環境有關的方式來格式化和解析日期的具體類。它允許進行格式化（日期 -> 文本）、解析（文本 -> 日期）和規範化。","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":"（1）日期和時間模式","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/24/2412cfe1a944dd2560648d2862a46fd8.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"}},{"type":"strong","attrs":{}}],"text":"（2）同步","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"日期格式是不同步的。建議爲每個線程創建獨立的格式實例。如果多個線程同時訪問一個格式，則它必須是外部同步的。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"2、NumberFormat","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"NumberFormat 是所有數值格式的抽象基類。此類提供格式化和解析數值的接口。NumberFormat 還提供了一些方法來確定哪些語言環境具有數值格式，以及它們的名稱是什麼。","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":"（1）DecimalFormat","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"DecimalFormat 是 NumberFormat 的一個具體子類，用於格式化十進制數字。該類設計有各種功能，使其能夠解析和格式化任意語言環境中的數，包括對西方語言、阿拉伯語和印度語數字的支持。它還支持不同類型的數，包括整數 (123)、定點數 (123.4)、科學記數法表示的數 (1.23E4)、百分數 (12%) 和金額 ($123)。所有這些內容都可以本地化。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"① 特殊模式字符","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"模式中的很多字符都是按字面解釋的；在解析期間對其進行匹配，在格式化期間則不經改變地輸出。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/86/86984f48c93b600375e1c18d929eba34.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":"② 舍入","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"DecimalFormat 提供 RoundingMode 中定義的舍入模式進行格式化。默認情況下，它使用 RoundingMode.HALF_EVEN。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"③ 同步","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"DecimalFormat 通常不是同步的。建議爲每個線程創建獨立的格式實例。如果多個線程同時訪問某個格式，則必須保持外部同步。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"示例","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/cf/cf234c7bb01445f7e59f79ae3da9dfe3.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}},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/be/be01235e58c26488d0f039182f37efcd.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"}},{"type":"strong","attrs":{}}],"text":"（2）ChoiceFormat","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"ChoiceFormat 允許將格式應用到某個範圍的數。它通常用於在 MessageFormat 中處理複數。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Choice 格式不是同步的。建議爲每個線程創建單獨的格式實例。如果多個線程併發訪問一個格式，則它必須保持外部同步。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"3、MessageFormat","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"MessageFormat 提供了以與語言無關的方式生成連接消息的方式。使用此方法構造向終端用戶顯示的消息。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"MessageFormat 獲取一組對象，格式化這些對象，然後將格式化後的字符串插入到模式中的適當位置。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"color","attrs":{"color":"#4D4D4D","name":"user"}}],"text":"示例：","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/f2/f26ecdf634263fb6930ad661bfbd2bc1.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","text":"輸出：The disk “MyDisk” contains 1,273 file(s).","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"注意：消息格式不是同步的。建議爲每個線程創建獨立的格式實例。如果多個線程同時訪問一個格式，則它必須是外部同步的。","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"五、隨機數類","attrs":{}}]},{"type":"heading","attrs":{"align":null,"level":1},"content":[{"type":"text","text":"1、Random 類","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Random 的對象能夠產生隨機數，他可以產生隨機整數、隨機float、隨機double，隨機long。","attrs":{}}]},{"type":"image","attrs":{"src":"https://static001.geekbang.org/infoq/28/28cd169738344b10c205e6a6e5b550dc.jpeg","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、Math 類的 random() 方法","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"Math 類的 random() 方法返回的數值是[0.0,1.0）的 double 型數值，可以對其進行運算和類型轉換獲得需要的隨機數。","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"獲得某個範圍的特定類型的隨機數：( 數據類型 )( 最小值 + Math.random() * ( 最大值 - 最小值 + 1 ) )","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"int a = (int)(30 + Math.random() * 71) // 生成[30，100]的隨機整數","attrs":{}}]},{"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":"小結","attrs":{}}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"以上是目前整理的一部分內容，如果有遺漏的歡迎大家補充！","attrs":{}}]},{"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":"#1F1F1F","name":"user"}}],"text":"今日份分享已結束，請大家多多包涵和指點！","attrs":{}}]}]}
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