类绑定----多态执行问题【编译看左，运行看右】

成员变量，静态方法看左边；非静态方法：编译看左边，运行看右边。

public class BoundDemo {
    public static void main(String[] args) {
        A a=new B();
        System.err.println(a.age);
        System.err.println(a.num);
        a.abc();
        a.abcd();
    }
    
}

class A
{
    public int age=100;
    public static int num=100;
    public static void abc()
    {
        System.err.println("100......");
    }
    public void abcd()
    {
        System.err.println("100.......");
    }
}

class B extends A
{
    public int age=1000;
    public static int num=1000;
    public static void abc()
    {
        System.err.println("1000......");
    }
    public void abcd()
    {
        System.err.println("1000.......");
    }
}