看着杨中科的解惑系列文章，突然想起把之前在《Core Java》上面看到的一段代码自己写一遍，就是不通过 main 方法实现 console 的 Hello world 输出。
自己原本是这样写的：
public class Main{
{ System.out.println("Hello,World!"); System.exit(0);
}
}
.csharpcode, .csharpcode pre{font-size: small;color: black;font-family: consolas, "Courier New", courier, monospace;background-color: #ffffff;/*white-space: pre;*/}.csharpcode pre { margin: 0em; }.csharpcode .rem { color: #008000; }.csharpcode .kwrd { color: #ffffff; }.csharpcode .str { color: #006080; }.csharpcode .op { color: #0000c0; }.csharpcode .preproc { color: #cc6633; }.csharpcode .asp { background-color: #ffff00; }.csharpcode .html { color: #800000; }.csharpcode .attr { color: #ff0000; }.csharpcode .alt {background-color: #ffffff;width: 100%;margin: 0em;}.csharpcode .lnum { color: #606060; }
程序运行老是提示 NoSuchMethodEroor ，我就很郁闷，书上明明是这样写的啊，在初始化一个类的时候一定会先初始化块……
Och，好像是记错了吧。块只有在初始化对象的时候才会被初始化，这个初始化类时候初始化的是静态玩意，呵呵，so ，代码只要加一个 static 就行了：
public class Main{
static{ System.out.println("Hello,World!"); System.exit(0);
}
}
.csharpcode, .csharpcode pre{font-size: small;color: black;font-family: consolas, "Courier New", courier, monospace;background-color: #ffffff;/*white-space: pre;*/}.csharpcode pre { margin: 0em; }.csharpcode .rem { color: #008000; }.csharpcode .kwrd { color: #0000ff; }.csharpcode .str { color: #006080; }.csharpcode .op { color: #0000c0; }.csharpcode .preproc { color: #cc6633; }.csharpcode .asp { background-color: #ffff00; }.csharpcode .html { color: #800000; }.csharpcode .attr { color: #ff0000; }.csharpcode .alt {background-color: #f4f4f4;width: 100%;margin: 0em;}.csharpcode .lnum { color: #606060; }
果真运行正常，图就不发了。
顺便总结一下 Java 类的初始化过程吧：
Java 类的初始化分为类初始化和对象初始化：
一、类初始化：
.csharpcode, .csharpcode pre{font-size: small;color: black;font-family: consolas, "Courier New", courier, monospace;background-color: #ffffff;/*white-space: pre;*/}.csharpcode pre { margin: 0em; }.csharpcode .rem { color: #008000; }.csharpcode .kwrd { color: #0000ff; }.csharpcode .str { color: #006080; }.csharpcode .op { color: #0000c0; }.csharpcode .preproc { color: #cc6633; }.csharpcode .asp { background-color: #ffff00; }.csharpcode .html { color: #800000; }.csharpcode .attr { color: #ff0000; }.csharpcode .alt {background-color: #f4f4f4;width: 100%;margin: 0em;}.csharpcode .lnum { color: #606060; }
二、对象初始化：
1、初始化父类构造方法；
2、初始化域与初始化块；
3、初始化自身构造方法；
.csharpcode, .csharpcode pre{font-size: small;color: black;font-family: consolas, "Courier New", courier, monospace;background-color: #ffffff;/*white-space: pre;*/}.csharpcode pre { margin: 0em; }.csharpcode .rem { color: #008000; }.csharpcode .kwrd { color: #0000ff; }.csharpcode .str { color: #006080; }.csharpcode .op { color: #0000c0; }.csharpcode .preproc { color: #cc6633; }.csharpcode .asp { background-color: #ffff00; }.csharpcode .html { color: #800000; }.csharpcode .attr { color: #ff0000; }.csharpcode .alt {background-color: #f4f4f4;width: 100%;margin: 0em;}.csharpcode .lnum { color: #606060; }
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感谢 Cay S.Horstmann 和 Gary Cornell 写出《Core Java》这本好书。
