小编OOP*_*OOP的帖子

public class Main { 
    /** 
      * @param args the command line arguments */ 
    public static void main(String[] args) { 
        // TODO code application logic here
        int a1 = 1000, a2 = 1000; 
        System.out.println(a1==a2);//=>true 
        Integer b1 = 1000, b2 = 1000;
        System.out.println(b1 == b2);//=>false 
        Integer c1 = 100, c2 = 100; 
        System.out.println(c1 == c2);//=>true 
    }

}

为什么是b1 == b2虚假和c1 == c2真实的？

请参阅以下代码:

package bk;

public class A { 
    protected void methodA() {
        System.out.println("Calling the method A !");
    }
}

// And I have an another package :   

package com;
import bk.A;

public class B extends A {
    public void methodB() {
        System.out.println("Goi phuong thuc B !");
    }

    public static void main(String[] args) {
         A a = new B();
         a.methodA();

    }
}

我怎么能a打电话methodA()？