类的加载顺序 (一、编译时常量与运行时常量)

落日映苍穹つ 2021-12-24 10:59 260阅读 0赞

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

转载于:https://www.cnblogs.com/chafanbusi/p/10639328.html