【转】浅析Java中的final关键字

末蓝、 2021-09-27 01:20 291阅读 0赞

参考：文章[https://www.cnblogs.com/dolphin0520/p/3736238.html][https_www.cnblogs.com_dolphin0520_p_3736238.html]

谈到final关键字，想必很多人都不陌生，在使用匿名内部类的时候可能会经常用到final关键字。另外，Java中的String类就是一个final类，那么今天我们就来了解final这个关键字的用法。下面是本文的目录大纲：

一.final关键字的基本用法

二.深入理解final关键字

若有不正之处，请多多谅解并欢迎指正。

请尊重作者劳动成果，转载请标明原文链接：

http://www.cnblogs.com/dolphin0520/p/3736238.html

## 一.final关键字的基本用法 ##

在Java中，final关键字可以用来修饰类、方法和变量（包括成员变量和局部变量）。下面就从这三个方面来了解一下final关键字的基本用法。

1.修饰类

当用final修饰一个类时，表明这个类不能被继承。也就是说，如果一个类你永远不会让他被继承，就可以用final进行修饰。final类中的成员变量可以根据需要设为final，但是要注意final类中的所有成员方法都会被隐式地指定为final方法。

![091032249893721.jpg][]

在使用final修饰类的时候，要注意谨慎选择，除非这个类真的在以后不会用来继承或者出于安全的考虑，尽量不要将类设计为final类。

2.修饰方法

下面这段话摘自《Java编程思想》第四版第143页：

“使用final方法的原因有两个。第一个原因是把方法锁定，以防任何继承类修改它的含义；第二个原因是效率。在早期的Java实现版本中，会将final方法转为内嵌调用。但是如果方法过于庞大，可能看不到内嵌调用带来的任何性能提升。在最近的Java版本中，不需要使用final方法进行这些优化了。“

因此，如果只有在想明确禁止 该方法在子类中被覆盖的情况下才将方法设置为final的。

注：类的private方法会隐式地被指定为final方法。

3.修饰变量

修饰变量是final用得最多的地方，也是本文接下来要重点阐述的内容。首先了解一下final变量的基本语法：

对于一个final变量，如果是基本数据类型的变量，则其数值一旦在初始化之后便不能更改；如果是引用类型的变量，则在对其初始化之后便不能再让其指向另一个对象。

举个例子：

![091114508325258.jpg][]

上面的一段代码中，对变量i和obj的重新赋值都报错了。

## 二.深入理解final关键字 ##

在了解了final关键字的基本用法之后，这一节我们来看一下final关键字容易混淆的地方。

1.类的final变量和普通变量有什么区别？

当用final作用于类的成员变量时，成员变量（注意是类的成员变量，局部变量只需要保证在使用之前被初始化赋值即可）必须在定义时或者构造器中进行初始化赋值，而且final变量一旦被初始化赋值之后，就不能再被赋值了。

那么final变量和普通变量到底有何区别呢？下面请看一个例子：

<table style="border-spacing:0px;border:1px solid #C0C0C0;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
 <tbody style="background:none;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
  <tr style="background:none;border-top:0px;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
   <td style="border-color:rgba(0,0,0,.35);color:rgb(0,0,0);border-collapse:collapse;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      1 
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    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      2 
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    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      3 
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      4 
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    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      5 
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    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      6 
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    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      7 
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    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      8 
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    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      9 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      10 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      11 
    </div></td> 
   <td style="border-color:#C0C0C0;border-collapse:collapse;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
    <div style="background:none;border:0px;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
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      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">Test { </code> 
     </div> 
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      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">static</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">void</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">main(String[] args)&nbsp; { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">String a =&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:#0000FF;">"hello2"</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">;&nbsp;</code> 
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     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">final</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">String b =&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:#0000FF;">"hello"</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">;</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">String d =&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:#0000FF;">"hello"</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">;</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
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      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">String c = b +&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,153,0);">2</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">;&nbsp;</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">String e = d +&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,153,0);">2</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">;</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
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      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println((a == c));</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println((a == e));</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

![ContractedBlock.gif][]

大家可以先想一下这道题的输出结果。为什么第一个比较结果为true，而第二个比较结果为fasle。这里面就是final变量和普通变量的区别了，当final变量是基本数据类型以及String类型时，如果在编译期间能知道它的确切值，则编译器会把它当做编译期常量使用。也就是说在用到该final变量的地方，相当于直接访问的这个常量，不需要在运行时确定。这种和C语言中的宏替换有点像。因此在上面的一段代码中，由于变量b被final修饰，因此会被当做编译器常量，所以在使用到b的地方会直接将变量b 替换为它的  值。而对于变量d的访问却需要在运行时通过链接来进行。想必其中的区别大家应该明白了，不过要注意，只有在编译期间能确切知道final变量值的情况下，编译器才会进行这样的优化，比如下面的这段代码就不会进行优化：

<table style="border-spacing:0px;border:1px solid #C0C0C0;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
 <tbody style="background:none;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
  <tr style="background:none;border-top:0px;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
   <td style="border-color:rgba(0,0,0,.35);color:rgb(0,0,0);border-collapse:collapse;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      1 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      2 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      3 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      4 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      5 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      6 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      7 
    </div> 
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      8 
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      9 
    </div> 
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      10 
    </div> 
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      11 
    </div> 
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      12 
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      13 
    </div></td> 
   <td style="border-color:#C0C0C0;border-collapse:collapse;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
    <div style="background:none;border:0px;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">class</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">Test { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">static</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">void</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">main(String[] args)&nbsp; { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">String a =&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:#0000FF;">"hello2"</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">;&nbsp;</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">final</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">String b = getHello();</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">String c = b +&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,153,0);">2</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">;&nbsp;</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println((a == c));</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;">
       &nbsp; 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code>&nbsp; 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">static</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">String getHello() { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">return</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:#0000FF;">"hello"</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">;</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

这段代码的输出结果为false。

2.被final修饰的引用变量指向的对象内容可变吗？

在上面提到被final修饰的引用变量一旦初始化赋值之后就不能再指向其他的对象，那么该引用变量指向的对象的内容可变吗？看下面这个例子：

这段代码可以顺利编译通过并且有输出结果，输出结果为1。这说明引用变量被final修饰之后，虽然不能再指向其他对象，但是它指向的对象的内容是可变的。

3.final和static

很多时候会容易把static和final关键字混淆，static作用于成员变量用来表示只保存一份副本，而final的作用是用来保证变量不可变。看下面这个例子：

<table style="border-spacing:0px;border:1px solid #C0C0C0;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
 <tbody style="background:none;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
  <tr style="background:none;border-top:0px;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
   <td style="border-color:rgba(0,0,0,.35);color:rgb(0,0,0);border-collapse:collapse;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      1 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      2 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      3 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      4 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      5 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      6 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      7 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      8 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      9 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      10 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      11 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      12 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      13 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      14 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      15 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      16 
    </div></td> 
   <td style="border-color:#C0C0C0;border-collapse:collapse;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
    <div style="background:none;border:0px;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">class</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">Test { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">static</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">void</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">main(String[] args)&nbsp; { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">MyClass myClass1 =&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">new</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">MyClass();</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">MyClass myClass2 =&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">new</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">MyClass();</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println(myClass1.i);</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println(myClass1.j);</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println(myClass2.i);</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println(myClass2.j);</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;">
       &nbsp; 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;">
       &nbsp; 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">class</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">MyClass { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">final</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">double</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">i = Math.random();</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">static</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">double</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">j = Math.random();</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

运行这段代码就会发现，每次打印的两个j值都是一样的，而i的值却是不同的。从这里就可以知道final和static变量的区别了。

4.匿名内部类中使用的外部局部变量为什么只能是final变量？

这个问题请参见上一篇博文中[《Java内部类详解》][Java]中的解释，在此处不再赘述。

5.关于final参数的问题

关于网上流传的”当你在方法中不需要改变作为参数的对象变量时，明确使用final进行声明，会防止你无意的修改而影响到调用方法外的变量“这句话，我个人理解这样说是不恰当的。

因为无论参数是基本数据类型的变量还是引用类型的变量，使用final声明都不会达到上面所说的效果。

看这个例子就清楚了：

![091522525043726.jpg][]

上面这段代码好像让人觉得用final修饰之后，就不能在方法中更改变量i的值了。殊不知，方法changeValue和main方法中的变量i根本就不是一个变量，因为java参数传递采用的是值传递，对于基本类型的变量，相当于直接将变量进行了拷贝。所以即使没有final修饰的情况下，在方法内部改变了变量i的值也不会影响方法外的i。

再看下面这段代码：

<table style="border-spacing:0px;border:1px solid #C0C0C0;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
 <tbody style="background:none;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
  <tr style="background:none;border-top:0px;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
   <td style="border-color:rgba(0,0,0,.35);color:rgb(0,0,0);border-collapse:collapse;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      1 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      2 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      3 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      4 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      5 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      6 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      7 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      8 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      9 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      10 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      11 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      12 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      13 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      14 
    </div> 
    <div style="background-color:rgb(193,230,198);border-color:rgba(0,0,0,.35);background-image:none;border-width:0px 2px 0px 0px;border-right-style:solid;line-height:1.8em;text-align:right;vertical-align:baseline;min-height:auto;">
      15 
    </div></td> 
   <td style="border-color:#C0C0C0;border-collapse:collapse;background:none;line-height:1.1em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;font-size:12px;min-height:auto;"> 
    <div style="background:none;border:0px;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">class</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">Test { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">public</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">static</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">void</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">main(String[] args)&nbsp; { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">MyClass myClass =&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">new</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">MyClass();</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">StringBuffer buffer =&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">new</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">StringBuffer(</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:#0000FF;">"hello"</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">);</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">myClass.changeValue(buffer);</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">System.out.println(buffer.toString());</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;">
       &nbsp; 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">class</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">MyClass { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code>&nbsp; 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">void</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">changeValue(</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,255);">final</code>&nbsp; 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">StringBuffer buffer) { </code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">buffer.append(</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:#0000FF;">"world"</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">);</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
     <div style="background-color:rgb(193,230,198);background-image:none;border:0px;line-height:1.8em;vertical-align:baseline;min-height:auto;"> 
      <code style="background:none;border:0px;line-height:1.8em;vertical-align:baseline;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;color:rgb(0,0,0);">}</code> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

运行这段代码就会发现输出结果为 helloworld。很显然，用final进行修饰并没有阻止在changeValue中改变buffer指向的对象的内容。有人说假如把final去掉了，万一在changeValue中让buffer指向了其他对象怎么办。有这种想法的朋友可以自己动手写代码试一下这样的结果是什么，如果把final去掉了，然后在changeValue中让buffer指向了其他对象，也不会影响到main方法中的buffer，原因在于java采用的是值传递，对于引用变量，传递的是引用的值，也就是说让实参和形参同时指向了同一个对象，因此让形参重新指向另一个对象对实参并没有任何影响。

所以关于网上流传的final参数的说法，我个人不是很赞同。

参考资料：

《Java编程思想》

作者： [海子][Link 1]

出处： [http://www.cnblogs.com/dolphin0520/][Link 1]

本博客中未标明转载的文章归作者 [海子][Link 1]和博客园共有，欢迎转载，但未经作者同意必须保留此段声明，且在文章页面明显位置给出原文连接，否则保留追究法律责任的权利。

[https_www.cnblogs.com_dolphin0520_p_3736238.html]: https://www.cnblogs.com/dolphin0520/p/3736238.html
[091032249893721.jpg]: /images/20210923/e3a9a234e06d41bd87fa9cc2ed5414aa.png
[091114508325258.jpg]: /images/20210923/c6a8daba289342859580411f3c519fda.png
[ContractedBlock.gif]: /images/20210923/e9c493c5b31b4c7c837ef633585f1d51.png
[Java]: http://www.cnblogs.com/dolphin0520/p/3811445.html
[091522525043726.jpg]: /images/20210923/e713ee0a3c684e368a726c9e79fce661.png
[Link 1]: http://www.cnblogs.com/dolphin0520/