java初始化顺序

<h1 style="font-family: verdana, sans-serif; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span style="font-weight: bold;"><span size="2" color="#7F0055"><strong><span style="color: rgb(65, 0, 125); font-family: 微软雅黑; orphans: 2; widows: 2;"><span style="font-size:32px;">1  无继承情况下的Java初始化顺序</span></span></strong></span></span></span></h1><p style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span style="font-size: 13px;"><span style="font-weight: bold;"><span size="2" color="#7F0055" style="font-size:10px;"><span style="font-size: 10pt;"><strong>class</strong></span></span> <span size="2" style="font-size:10px;"><span style="font-size: 10pt;">Sample</span></span></span></span></span></p><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">{</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      Sample(String s)</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      {</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">            System.</span></span><span size="2" color="#0000C0" style="color: rgb(0, 0, 192);font-size:10px;"><span style="font-size: 10pt;"><em>out</em></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">.println(s);</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      }</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      Sample()</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      {</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">            System.</span></span><span size="2" color="#0000C0" style="color: rgb(0, 0, 192);font-size:10px;"><span style="font-size: 10pt;"><em>out</em></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">.println(</span></span><span size="2" color="#2A00FF" style="color: rgb(42, 0, 255);font-size:10px;"><span style="font-size: 10pt;">"Sample默认构造函数被调用"</span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">);</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      }</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">}</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" color="#7F0055" style="font-size:10px;"><span style="font-size: 10pt;"><strong>class</strong></span></span> <span size="2" style="font-size:10px;"><span style="font-size: 10pt;">Test{</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      </span></span><span size="2" color="#7F0055" style="font-size:10px;"><span style="font-size: 10pt;"><strong>static</strong></span></span> <span size="2" style="font-size:10px;"><span style="font-size: 10pt;">Sample</span></span> <span size="2" color="#0000C0" style="color: rgb(0, 0, 192);font-size:10px;"><span style="font-size: 10pt;"><em>sam</em></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">=</span></span><span size="2" color="#7F0055" style="font-size:10px;"><span style="font-size: 10pt;"><strong>new</strong></span></span> <span size="2" style="font-size:10px;"><span style="font-size: 10pt;">Sample(</span></span><span size="2" color="#2A00FF" style="color: rgb(42, 0, 255);font-size:10px;"><span style="font-size: 10pt;">"静态成员sam初始化"</span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">);</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      Sample</span></span> <span size="2" color="#0000C0" style="color: rgb(0, 0, 192);font-size:10px;"><span style="font-size: 10pt;">sam1</span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">=</span></span><span size="2" color="#7F0055" style="font-size:10px;"><span style="font-size: 10pt;"><strong>new</strong></span></span> <span size="2" style="font-size:10px;"><span style="font-size: 10pt;">Sample(</span></span><span size="2" color="#2A00FF" style="color: rgb(42, 0, 255);font-size:10px;"><span style="font-size: 10pt;">"sam1成员初始化"</span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">);</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      </span></span><span size="2" color="#7F0055" style="font-size:10px;"><span style="font-size: 10pt;"><strong>static</strong></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">{</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">            System.</span></span><span size="2" color="#0000C0" style="color: rgb(0, 0, 192);font-size:10px;"><span style="font-size: 10pt;"><em>out</em></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">.println(</span></span><span size="2" color="#2A00FF" style="color: rgb(42, 0, 255);font-size:10px;"><span style="font-size: 10pt;">"static块执行"</span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">);</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">            </span></span><span size="2" color="#7F0055" style="font-size:10px;"><span style="font-size: 10pt;"><strong>if</strong></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">(</span></span><span size="2" color="#0000C0" style="color: rgb(0, 0, 192);font-size:10px;"><span style="font-size: 10pt;"><em>sam</em></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">==</span></span><span size="2" color="#7F0055" style="font-size:10px;"><span style="font-size: 10pt;"><strong>null</strong></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">)System.</span></span><span size="2" color="#0000C0" style="color: rgb(0, 0, 192);font-size:10px;"><span style="font-size: 10pt;"><em>out</em></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">.println(</span></span><span size="2" color="#2A00FF" style="color: rgb(42, 0, 255);font-size:10px;"><span style="font-size: 10pt;">"sam is null"</span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">);</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">            </span></span><span size="2" color="#0000C0" style="color: rgb(0, 0, 192);font-size:10px;"><span style="font-size: 10pt;"><em>sam</em></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">=</span></span><span size="2" color="#7F0055" style="font-size:10px;"><span style="font-size: 10pt;"><strong>new</strong></span></span> <span size="2" style="font-size:10px;"><span style="font-size: 10pt;">Sample(</span></span><span size="2" color="#2A00FF" style="color: rgb(42, 0, 255);font-size:10px;"><span style="font-size: 10pt;">"静态块内初始化sam成员变量"</span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">);</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">            }</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      Test()</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      {</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">            System.</span></span><span size="2" color="#0000C0" style="color: rgb(0, 0, 192);font-size:10px;"><span style="font-size: 10pt;"><em>out</em></span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">.println(</span></span><span size="2" color="#2A00FF" style="color: rgb(42, 0, 255);font-size:10px;"><span style="font-size: 10pt;">"Test默认构造函数被调用"</span></span><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">);</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span size="2" style="font-size:10px;"><span style="font-size: 10pt;">      }</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span face="Courier New" size="2" color="#010101" style="color: rgb(1, 1, 1); font-family: 'Courier New';font-size:10px;"><span style="font-size: 10pt;">
</span></span></span></div><div align="left" style="font-family: verdana, sans-serif; font-size: 13px; line-height: 19.5px;"><span face="Consolas" color="#7F0055" style="color: rgb(127, 0, 85); font-family: Consolas;"><span face="Courier New" size="2" style="font-family: 'Courier New';font-size:10px;"><span style="font-size: 10pt;">}</span></span></span></div>

输出结果为：

静态成员sam初始化     -----静态成员初始化

static块执行          -----静态块被执行

静态块内初始化sam成员变量 ----静态块执行

sam1成员初始化      -----普通成员初始化

Test默认构造函数被调用  -----构造函数执行

由此可以得出结论：

a 静态成员变量首先初始化（注意，Static可以看做一个静态成员，其执行顺序和其在类中申明的顺序有关）

b 普通成员初始化

c 执行构造函数。

对于静态成员（static块可以看成普通的一个静态成员，其并不一定在类初始化时首先执行）和普通成员，其初始化顺序只与其在类定义中的顺序有关，和其他因素无关。

例如下面的例子：

class Test{
static{
System.out.println("static 块 1  执行");
}
static Sample staticSam1=new Sample("静态成员staticSam1初始化");
Sample sam1=new Sample("sam1成员初始化");
static Sample staticSam2=new Sample("静态成员staticSam2初始化");
static{
System.out.println("static 块 2  执行");
}
Test()
{
System.out.println("Test默认构造函数被调用");
}
Sample sam2=new Sample("sam2成员初始化");

}

则结果为：

[align=left]static 块 1  执行[/align]
[align=left]静态成员staticSam1初始化[/align]
[align=left]静态成员staticSam2初始化[/align]
static
块 2  执行 
  
                   --------静态成员
[align=left]sam1成员初始化[/align]
[align=left]sam2成员初始化[/align]
  
                   --------普通成员
[align=left]Test默认构造函数被调用[/align]
  
                   --------构造函数
[align=left]
[/align]

2 Java继承情况下的初始化顺序：

class Test{
static{
System.out.println("父类static 块 1  执行");
}
static Sample staticSam1=new Sample("父类 静态成员staticSam1初始化");
Sample sam1=new Sample("父类 sam1成员初始化");
static Sample staticSam2=new Sample("父类 静态成员staticSam2初始化");
static{
System.out.println("父类 static 块 2  执行");
}
Test()
{
System.out.println("父类 Test默认构造函数被调用");
}
Sample sam2=new Sample("父类 sam2成员初始化");

}

class TestSub extends Test
{
static Sample staticSamSub=new Sample("子类 静态成员staticSamSub初始化");
TestSub()
{
System.out.println("子类 TestSub 默认构造函数被调用");
}
Sample sam1=new Sample("子类 sam1成员初始化");
static Sample staticSamSub1=new Sample("子类 静态成员staticSamSub1初始化");

static{System.out.println("子类 static 块  执行");}
Sample sam2=new Sample("子类 sam2成员初始化");
}

执行结果：

父类 static
块 1  执行
[align=left]父类 静态成员staticSam1初始化[/align]
[align=left]父类 静态成员staticSam2初始化[/align]
[align=left]父类 static 块 2  执行[/align]
                      
 --------父类静态成员初始化
[align=left]子类 静态成员staticSamSub初始化[/align]
[align=left]子类 静态成员staticSamSub1初始化[/align]
[align=left]子类 static 块  执行[/align]
                      
 -------子类静态成员初始化
[align=left]父类 sam1成员初始化[/align]
[align=left]父类 sam2成员初始化[/align]
[align=left]父类 Test默认构造函数被调用       [/align]
                      
 -------父类普通成员初始化和构造函数执行
[align=left]子类 sam1成员初始化[/align]
[align=left]子类 sam2成员初始化[/align]
[align=left]子类 TestSub 默认构造函数被调用[/align]
[align=left]                        -------父类普通成员初始化和构造函数执行[/align]
[align=left]
[/align]
[align=left]
[/align]
[align=left]由此得出Java初始化顺序结论：[/align]
[align=left]1 继承体系的所有静态成员初始化（先父类，后子类）[/align]
[align=left]2 父类初始化完成（普通成员的初始化-->构造函数的调用）[/align]
[align=left]3 子类初始化（普通成员-->构造函数）[/align]
[align=left]
[/align]
[align=left]
[/align]
[align=left]Java初始化顺序如图：[/align]