從一道SCJP 試題來看你對繼承和多態的理解程度? csdn)

What is displayed when the following is executed?

class Parent{
   private void method1(){
     System.out.println("Parent's method1()");
   }
  public void method2()
  {
    System.out.println("Parent's method2()");
    method1();
  }
}

class Child extends Parent{
  public void method1(){
    System.out.println("Child's method1()");
  }

  public static void main(String args[]){

  Parent p = new Child();
  p.method2();
  }

}

Choices:

a. Compile time error

b. Run time error

c. prints : Parent's method2()

          Parent's method1()

d. prints : Parent's method2()

          Child's method1()

 

 

答案是C

但是我們把題改一下,

class Parent{
   private void method1(){
     System.out.println("Parent's method1()");
   }
  public void method2()
  {
    System.out.println("Parent's method2()");
    method1();
  }
}

class Child extends Parent{
  public void method1(){
    System.out.println("Child's method1()");
  }

  public static void main(String args[]){

  Child p = new Child();//改變了這裡

  p.method2();
  }

}

應該選什麼? 也是C!

我們再改一下:

class Parent{
   public  void method1(){  //change here
     System.out.println("Parent's method1()");
   }
  public void method2()
  {
    System.out.println("Parent's method2()");
    method1();
  }
}

class Child extends Parent{
  public void method1(){
    System.out.println("Child's method1()");
  }

  public static void main(String args[]){

  Parent p = new Child();
  p.method2();
  }

}

 

這次終於是答案D了,我們再改
:

class Parent{
   public  void method1(){  //change here
     System.out.println("Parent's method1()");
   }
  public void method2()
  {
    System.out.println("Parent's method2()");
    method1();
  }
}

class Child extends Parent{
  public void method1(){
    System.out.println("Child's method1()");
  }

  public static void main(String args[]){

  Child p = new Child();//change here
  p.method2();
  }

}

也是答案D,我這裡是運行過的結果,可是不理解為什麼,那個高手跳出來解釋一下?

參考貼:
http://community.csdn.net/Expert/topic/3490/3490386.xml?temp=.3488581