d.java

java课件及例程有一些PPT及一些例程

class A
{
    int x=3;
    public void m()
    {
        System.out.println("the x of A is "+x);
    }
}
class B extends A
{
    double y=2;  
    public void n()
    {
        y--;
        System.out.println("y= "+y+",x= "+x);  
    }    
}
class D{
    public static void main(String[] args)
    {
        B ref_b,b;
        b = new B();
        A a;
        //a=new A();
        //b=(B)a;
        a=b;
        if (a instanceof B){
        //try{
        ref_b=(B)a; 
        System.out.println("a.x="+a.x);
        System.out.println("ref_b.x="+ref_b.x+", ref_b.y= "+ref_b.y);
       // }catch(Exception e){}
       }
        System.out.println("hello");
              	
    }
}