Java数据类型包装器

朱雀 2022-09-30 12:51 204阅读 0赞

Java库在`java.lang`包中提供了八个类来表示八种基本类型中的每一种。这些类称为包装类，因为它们在对象中包装原始值。  
下表列出了原始类型及其相应的包装类。

<table style="margin:0px 0px 18px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(221,221,221) rgb(187,187,187) rgb(187,187,187) rgb(221,221,221); outline:none; border-spacing:0px; font-size:14px; width:840px; color:rgb(51,51,68); font-family:&quot;Helvetica Neue&quot;,Helvetica,Arial,&quot;Microsoft Yahei&quot;,&quot;Hiragino Sans GB&quot;,&quot;Heiti SC&quot;,&quot;WenQuanYi Micro Hei&quot;,sans-serif; widows:2"> 
 <thead style=""> 
  <tr style=""> 
   <th style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none; text-align:center; background-color:rgb(249,249,249)"> 基本类型</th> 
   <th style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none; text-align:center; background-color:rgb(249,249,249)"> 包装类</th> 
  </tr> 
 </thead> 
 <tbody style=""> 
  <tr style=""> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> byte</td> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> Byte</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> short</td> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> Short</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> int</td> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> Integer</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> long</td> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> Long</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> float</td> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> Float</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> double</td> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> Double</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> char</td> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> Character</td> 
  </tr> 
  <tr style=""> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> boolean</td> 
   <td style="padding:5px 10px; border-collapse:collapse; border-width:1px; border-style:solid; border-color:rgb(187,187,187) rgb(221,221,221) rgb(221,221,221) rgb(187,187,187); height:28px; word-break:break-all; outline:none"> Boolean</td> 
  </tr> 
 </tbody> 
</table>

## 方法 ##

所有包装类都是不可变的。 它们提供了两种方法来创建它们的对象：

*  使用构造函数
 *  使用`valueOf()`工厂方法

除了`Character`之外，每个包装类都提供至少两个构造函数：一个采用对应基本类型的值，另一个采用`String`类型值。

`Character`类只提供一个接受`char`的构造函数。

## 示例 ##

以下代码创建一些包装类的对象：

\[AD\]

public class Main { public static void staticMethod() { // Creates an Integer object from an int Integer intObj1 = new Integer(100); // Creates an Integer object from a String Integer intObj2 = new Integer("1969"); // Creates a Double object from a double Double doubleObj1 = new Double(10.45); // Creates a Double object from a String Double doubleObj2 = new Double("234.60"); // Creates a Character object from a char Character charObj1 = new Character('A'); // Creates a Boolean object from a boolean Boolean booleanObj1 = new Boolean(true); // Creates Boolean objects from Strings Boolean booleanTrue = new Boolean("true"); Boolean booleanFalse = new Boolean("false"); } } 
      
       Java

## valueOf() ##

创建包装类对象的另一种方法是使用它们的`valueOf()`方法。`valueOf()`方法是一个静态的方法。  
以下代码使用它们的`valueOf()`方法创建一些包装器类的对象：

public class Main { public static void staticMethod() { Integer intObj1 = Integer.valueOf(100); Integer intObj2 = Integer.valueOf("2014"); Double doubleObj1 = Double.valueOf(10.45); Double doubleObj2 = Double.valueOf("234.56"); Character charObj1 = Character.valueOf('A'); } }