类的加载顺序 (一、编译时常量与运行时常量)

编译时常量在编译阶段会写死到.class中

而且会存入到 调用这个常量的方法所在的类的常量池中

如下代码编译后 删除Parents01.class 后依然可以正常执行

public class MyTest01 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		System.out.println(Parents01.VALUE);
	}
	

}
class Parents01{
	public static final String VALUE = "Parents01 const VALUE";
	static {
		System.out.println("this is Parents01 static block");
	}
}//out：Parents01 const VALUE

说明VALUE被写入了MyTest01中

运行时常量：(编译时不加载，类初始化时才加载）

public class MyTest01 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		System.out.println(Parents01.VALUE);
	}
	

}
class Parents01{
	public static final String VALUE = new String("Parents01 const VALUE");
	static {
		System.out.println("this is Parents01 static block");
	}
}//out：Parents01 const VALUE

　　

另外 用子类调用父类的 static字段 并不会初始化子类static域

具体代码如下

public class MyTest01 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		System.out.println(Children01.VALUE);
	}
	

}
class Parents01{
	public static String VALUE = "Parents01 const VALUE";
	static {
		System.out.println("this is Parents01 static block");
	}
}

class Children01 extends Parents01{
	static {
		System.out.println("this is Children01 static block");
	}
}
//~out：

this is Parents01 static block
Parents01 const VALUE

　　将VALUE修改为final 则 一个static域都不执行。

static域在static字段后初始化，父类先于子类初始化:

public class MyTest01 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		new Children01();
	}
	

}
class Parents01{
	public static Sub01 sub = new Sub01();
	static {
		System.out.println("this is Parents01 static block");
	}
}

class Children01 extends Parents01{
	static {
		System.out.println("this is Children01 static block");
	}
}
class Sub01{
	Sub01(){
		System.out.println("this is Sub01");
	}
}
//~out:
this is Sub01
this is Parents01 static block
this is Children01 static block