继承与多态的理解


public class Base {

public static int s;
private int a ;

static
{
System.out.println("基类静态代码块,s:"+s);
}

{
System.out.println("基类实例代码快,a:"+a);

}

public Base()
{
System.out.println("基类构造方法,a:"+a);
a=2;
}

protected void step()
{
System.out.println("base ,s:"+s + ",a:"+ a);

}

public void action()
{
System.out.println("start");
step();
System.out.println("end");


}
}


public class Base {

public static int s;
private int a ;

static
{
System.out.println("基类静态代码块,s:"+s);
}

{
System.out.println("基类实例代码快,a:"+a);

}

public Base()
{
System.out.println("基类构造方法,a:"+a);
a=2;
}

protected void step()
{
System.out.println("base ,s:"+s + ",a:"+ a);

}

public void action()
{
System.out.println("start");
step();
System.out.println("end");


}
}

 

 

 


public class Child extends Base{

public static String s;
private int a;

static
{
System.out.println("子类静态代码快,s:"+s);
}

{
System.out.println("子类实例代码快,a:"+a);
a=10;

}

public Child()
{
System.out.println("子类构造方法:a:" + a);
a = 20;
}

protected void step()
{
System.out.println("Child ,s:"+s + ",a:"+ a);
}

public static void main (String[] args)
{
System.out.println("---new Child()---begin");
Child child = new Child();
System.out.println("---new Child()----end --");

System.out.println("\n---child.action()");
child.action();

Base base = child ;
System.out.println("\n---base.action()");
base.action();

System.out.println("\n---base.s" + base.s);
System.out.println("\n---child.s" + child.s);

}

}

 

 

执行结果为:

基类静态代码块,s:0
子类静态代码快,s:null
---new Child()---begin
基类实例代码快,a:0
基类构造方法,a:0
子类实例代码快,a:0
子类构造方法:a:10
---new Child()----end --

---child.action()
start
Child ,s:null,a:20
end

---base.action()
start
Child ,s:null,a:20
end

---base.s0

---child.snull

 

执行顺序为:

 基类静态代码块 >> 子类静态代码快  >>  基类实例代码快  >>  基类构造方法  >>  子类实例代码快 >>  子类构造方法 

 

且静态代码块只加载一次,是在加载类的时候加载的。每new一个对象时,静态代码块会重新加载一次。

posted @ 2016-12-01 18:00  SUPERUSR  阅读(185)  评论(0编辑  收藏  举报