JAVA的包装类

约定不等于承诺〃 2022-06-02 12:36 178阅读 0赞

Java语言是一个面向对象的语言，但是Java中的基本数据类型却是不面向对象的，这在实际使用时存在很多的不便，为了解决这个不足，在设计类时为每个基本数据类型设计了一个对应的类进行代表，这样八个和基本数据类型对应的类统称为包装类(Wrapper Class)，有些地方也翻译为外覆类或数据类型类。

包装类均位于java.lang包，包装类和基本数据类型的对应关系如下表所示：

包装类对应表

<table style="margin-top:auto; margin-right:auto; margin-bottom:auto; margin-left:55.05pt; border-top-width:1px; border-right-width:1px; border-bottom-width:1px; border-left-width:1px; border-top-style:solid; border-right-style:solid; border-bottom-style:solid; border-left-style:solid; border-top-color:rgb(192,192,192); border-right-color:rgb(192,192,192); border-bottom-color:rgb(192,192,192); border-left-color:rgb(192,192,192); border-collapse:collapse"> 
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 <td style="border-top-width:1pt; border-right-width:1pt; border-bottom-width:1pt; border-left-width:medium; border-top-style:solid; border-right-style:solid; border-bottom-style:solid; border-left-style:none; border-top-color:black; border-right-color:black; border-bottom-color:black; border-left-color:rgb(212,208,200); border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:120.5pt; background-color:transparent"> 包装类 </td> 
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 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:1pt; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:solid; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:black; border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:106.3pt; background-color:transparent"> byte </td> 
 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:medium; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:none; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:rgb(212,208,200); border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:120.5pt; background-color:transparent"> Byte </td> 
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 <tr> 
 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:1pt; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:solid; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:black; border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:106.3pt; background-color:transparent"> boolean </td> 
 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:medium; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:none; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:rgb(212,208,200); border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:120.5pt; background-color:transparent"> Boolean </td> 
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 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:1pt; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:solid; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:black; border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:106.3pt; background-color:transparent"> short </td> 
 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:medium; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:none; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:rgb(212,208,200); border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:120.5pt; background-color:transparent"> Short </td> 
 </tr> 
 <tr> 
 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:1pt; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:solid; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:black; border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:106.3pt; background-color:transparent"> char </td> 
 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:medium; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:none; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:rgb(212,208,200); border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:120.5pt; background-color:transparent"> Character </td> 
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 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:1pt; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:solid; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:black; border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:106.3pt; background-color:transparent"> int </td> 
 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:medium; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:none; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:rgb(212,208,200); border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:120.5pt; background-color:transparent"> Integer </td> 
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 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:1pt; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:solid; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:black; border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:106.3pt; background-color:transparent"> long </td> 
 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:medium; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:none; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:rgb(212,208,200); border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:120.5pt; background-color:transparent"> Long </td> 
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 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:1pt; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:solid; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:black; border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:106.3pt; background-color:transparent"> float </td> 
 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:medium; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:none; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:rgb(212,208,200); border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:120.5pt; background-color:transparent"> Float </td> 
 </tr> 
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 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:1pt; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:solid; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:black; border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:106.3pt; background-color:transparent"> double </td> 
 <td style="border-top-width:medium; border-right-width:1pt; border-bottom-width:1pt; border-left-width:medium; border-top-style:none; border-right-style:solid; border-bottom-style:solid; border-left-style:none; border-top-color:rgb(212,208,200); border-right-color:black; border-bottom-color:black; border-left-color:rgb(212,208,200); border-collapse:collapse; padding-top:0cm; padding-right:5.4pt; padding-bottom:0cm; padding-left:5.4pt; width:120.5pt; background-color:transparent"> Double </td> 
 </tr> 
 </tbody> 
</table>

在这八个类名中，除了Integer和Character类以后，其它六个类的类名和基本数据类型一直，只是类名的第一个字母大写即可。

对于包装类说，这些类的用途主要包含两种：

a、作为和基本数据类型对应的类类型存在，方便涉及到对象的操作。

b、包含每种基本数据类型的相关属性如最大值、最小值等，以及相关的操作方法。

由于八个包装类的使用比较类似，下面以最常用的Integer类为例子介绍包装类的实际使用。

1、实现int和Integer类之间的转换

在实际转换时，使用Integer类的构造方法和Integer类内部的intValue方法实现这些类型之间的相互转换，实现的代码如下：

int n = 10;

Integer in = new Integer(100);

//将int类型转换为Integer类型

Integer in1 = new Integer(n);

//将Integer类型的对象转换为int类型