Java GC的那些事（上）

叁歲伎倆 2022-05-24 13:13 142阅读 0赞

### 前言 ###

与C语言不同，Java内存（堆内存）的分配与回收由JVM垃圾收集器自动完成，这个特性深受大家欢迎，能够帮助程序员更好的编写代码，本文以HotSpot虚拟机为例，说一说Java GC的那些事。

### Java堆内存 ###

在 [JVM内存的那些事][JVM] 一文中，我们已经知道Java堆是被所有线程共享的一块内存区域，所有对象实例和数组都在堆上进行内存分配。为了进行高效的垃圾回收，虚拟机把堆内存划分成新生代（Young Generation）、老年代（Old Generation）和永久代（Permanent Generation）3个区域。

![1240][]

#### 新生代 ####

新生代由 Eden 与 Survivor Space（S0，S1）构成，大小通过-Xmn参数指定，Eden 与 Survivor Space 的内存大小比例默认为8:1，可以通过-XX:SurvivorRatio 参数指定，比如新生代为10M 时，Eden分配8M，S0和S1各分配1M。

Eden：希腊语，意思为伊甸园，在圣经中，伊甸园含有乐园的意思，根据《旧约·创世纪》记载，上帝耶和华照自己的形像造了第一个男人亚当，再用亚当的一个肋骨创造了一个女人夏娃，并安置他们住在了伊甸园。

大多数情况下，对象在Eden中分配，当Eden没有足够空间时，会触发一次Minor GC，虚拟机提供了-XX:+PrintGCDetails参数，告诉虚拟机在发生垃圾回收时打印内存回收日志。

Survivor：意思为幸存者，是新生代和老年代的缓冲区域。  
当新生代发生GC（Minor GC）时，会将存活的对象移动到S0内存区域，并清空Eden区域，当再次发生Minor GC时，将Eden和S0中存活的对象移动到S1内存区域。

存活对象会反复在S0和S1之间移动，当对象从Eden移动到Survivor或者在Survivor之间移动时，对象的GC年龄自动累加，当GC年龄超过默认阈值15时，会将该对象移动到老年代，可以通过参数-XX:MaxTenuringThreshold 对GC年龄的阈值进行设置。

#### 老年代 ####

老年代的空间大小即-Xmx 与-Xmn 两个参数之差，用于存放经过几次Minor GC之后依旧存活的对象。当老年代的空间不足时，会触发Major GC/Full GC，速度一般比Minor GC慢10倍以上。

#### 永久代 ####

在JDK8之前的HotSpot实现中，类的元数据如方法数据、方法信息（字节码，栈和变量大小）、运行时常量池、已确定的符号引用和虚方法表等被保存在永久代中，32位默认永久代的大小为64M，64位默认为85M，可以通过参数-XX:MaxPermSize进行设置，一旦类的元数据超过了永久代大小，就会抛出OOM异常。

虚拟机团队在JDK8的HotSpot中，把永久代从Java堆中移除了，并把类的元数据直接保存在本地内存区域（堆外内存），称之为元空间。

这样做有什么好处？  
有经验的同学会发现，对永久代的调优过程非常困难，永久代的大小很难确定，其中涉及到太多因素，如类的总数、常量池大小和方法数量等，而且永久代的数据可能会随着每一次Full GC而发生移动。

而在JDK8中，类的元数据保存在本地内存中，元空间的最大可分配空间就是系统可用内存空间，可以避免永久代的内存溢出问题，不过需要监控内存的消耗情况，一旦发生内存泄漏，会占用大量的本地内存。

ps：JDK7之前的HotSpot，字符串常量池的字符串被存储在永久代中，因此可能导致一系列的性能问题和内存溢出错误。在JDK8中，字符串常量池中只保存字符串的引用。

### 如何判断对象是否存活 ###

GC动作发生之前，需要确定堆内存中哪些对象是存活的，一般有两种方法：引用计数法和可达性分析法。

1、引用计数法  
在对象上添加一个引用计数器，每当有一个对象引用它时，计数器加1，当使用完该对象时，计数器减1，计数器值为0的对象表示不可能再被使用。

引用计数法实现简单，判定高效，但不能解决对象之间相互引用的问题。

通过添加-XX:+PrintGC参数，运行结果：

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      1 
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   <td style="width:638px;border-width:0px;margin:0px;padding:0px;font-size:12px;vertical-align:baseline;background:none;float:none;height:auto;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;"> 
    <div style="margin-left:-10px;width:640px;border:0px;margin-top:0px;margin-right:0px;margin-bottom:0px;padding:0px;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">[GC (System.gc()) [PSYoungGen: 26982K-&gt;1194K(75776K)] 26982K-&gt;1202K(249344K), </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">0.0010103</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">secs]</code> 
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从GC日志中可以看出objA和objB虽然相互引用，但是它们所占的内存还是被垃圾收集器回收了。

2、可达性分析法  
通过一系列称为 “GC Roots” 的对象作为起点，从这些节点开始向下搜索，搜索路径称为 “引用链”，以下对象可作为GC Roots：

*  本地变量表中引用的对象
 *  方法区中静态变量引用的对象
 *  方法区中常量引用的对象
 *  Native方法引用的对象

当一个对象到 GC Roots 没有任何引用链时，意味着该对象可以被回收。

![1240 1][]

在可达性分析法中，判定一个对象objA是否可回收，至少要经历两次标记过程：  
1、如果对象objA到 GC Roots没有引用链，则进行第一次标记。  
2、如果对象objA重写了finalize()方法，且还未执行过，那么objA会被插入到F-Queue队列中，由一个虚拟机自动创建的、低优先级的Finalizer线程触发其finalize()方法。finalize()方法是对象逃脱死亡的最后机会，GC会对队列中的对象进行第二次标记，如果objA在finalize()方法中与引用链上的任何一个对象建立联系，那么在第二次标记时，objA会被移出“即将回收”集合。

看看具体实现

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    <div style="border-width:0px 3px 0px 0px;border-right-style:solid;border-right-color:rgb(108,226,108);margin:0px;padding:0px .5em 0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;text-align:right;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;">
      39 
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   <td style="width:585px;border-width:0px;margin:0px;padding:0px;font-size:12px;vertical-align:baseline;background:none;float:none;height:auto;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;min-height:auto;"> 
    <div style="margin-left:-10px;width:640px;border:0px;margin-top:0px;margin-right:0px;margin-bottom:0px;padding:0px;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;min-height:auto;"> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">public</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">class</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">FinalizerTest { </code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">public</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">static</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">FinalizerTest object;</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">public</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">void</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">isAlive() { </code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">System.out.println(</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#0000FF;">"I'm alive"</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">);</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">}</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;">
       &nbsp; 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#808080;">@Override</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">protected</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">void</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">finalize() </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">throws</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Throwable { </code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">super</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">.finalize();</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">System.out.println(</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#0000FF;">"method finalize is running"</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">);</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">object = </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">this</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">;</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">}</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;">
       &nbsp; 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">public</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">static</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">void</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">main(String[] args) </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">throws</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Exception { </code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">object = </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">new</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">FinalizerTest();</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;">
       &nbsp; 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,130,0);">// 第一次执行，finalize方法会自救</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">object = </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">null</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">;</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">System.gc();</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;">
       &nbsp; 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Thread.sleep(</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">500</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">);</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">if</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">(object != </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">null</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">) { </code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">object.isAlive();</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">} </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">else</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">{ </code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">System.out.println(</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#0000FF;">"I'm dead"</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">);</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">}</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;">
       &nbsp; 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,130,0);">// 第二次执行，finalize方法已经执行过</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">object = </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">null</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">;</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">System.gc();</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;">
       &nbsp; 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">Thread.sleep(</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:rgb(0,153,0);">500</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">);</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">if</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">(object != </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">null</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">) { </code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">object.isAlive();</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">} </code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;font-weight:bold;min-height:auto;color:rgb(0,102,153);">else</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">{ </code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">System.out.println(</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#0000FF;">"I'm dead"</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">);</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">}</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;">&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">}</code> 
     </div> 
     <div style="border:0px;margin:0px;padding:0px 1em;background-image:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;white-space:pre;"> 
      <code style="border:0px;margin:0px;padding:0px;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;background:none;float:none;height:auto;line-height:1.1em;vertical-align:baseline;width:auto;min-height:auto;color:#000000;">}</code> 
     </div> 
    </div></td> 
  </tr> 
 </tbody> 
</table>

执行结果：

从执行结果可以看出：  
第一次发生GC时，finalize方法的确执行了，并且在被回收之前成功逃脱；  
第二次发生GC时，由于finalize方法只会被JVM调用一次，object被回收。

当然了，在实际项目中应该尽量避免使用finalize方法。

[JVM]: http://www.importnew.com/?p=23629
[1240]: /images/20220524/76bd75c2801a448a9ec54c7cf21b3a2e.png
[1240 1]: /images/20220524/ca3460aea2224dcdb36d20a8606e9450.png