Java开发网 - 关于equals()方法的困惑

Topic: 关于equals()方法的困惑

1.关于equals()方法的困惑

Posted by: zmj888
Posted on: 2005-12-08 12:51

class Triple1 {

private int x1,x2,x3;
public Triple1(){
this(0,0,0);
}
public Triple1(int a,int b,int c){
setValue(1,a);
setValue(2,b);
setValue(3,c);
}

public void setValue(int i,int value){
switch( i ){
case 1:x1=value;return;
case 2:x2=value;return;
case 3:x3=value;return;
default:
System.err.println("error");
System.exit(1);
}
}

}

class triple{
public static void main(String args[]){
Triple1 h=new Triple1(1,1,1);
Triple1 t=new Triple1(1,1,1);

System.out.println(h.equals( t ));
// System.out.println(h=t);
System.out.println(h==t);
}
}

上面代码运行结果是
false
false

为什么加入红色那段代码运行结果就变了呢
false
Triple1@757aef
ture

2.Re:关于equals()方法的困惑 [Re: zmj888]

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Posted by: ntshenwh
Posted on: 2005-12-08 13:11

hi,
your code seems not correct. I updated these as follows:

class triple
{

  private int x1,x2,x3;

  public triple()
  {
    this(0,0,0);
  }

  public triple(int a,int b,int c)
  {
    setValue(1,a);
    setValue(2,b);
    setValue(3,c);
  }

  public void setValue(int i,int value)
  {
  switch( i )
    {
      case 1:x1=value;return;
      case 2:x2=value;return;
      case 3:x3=value;return;
      default:
      System.err.println("error");
      System.exit(1);
    }
  }

  public static void main(String args[])
  {
    triple h=new triple(1,1,1);
    triple t=new triple(1,1,1);

    System.out.println(h.equals( t ));
    System.out.println(h==t);
  }
}

// here , both equals() and == are all compare the reference of objects.
the result is
false
false

good luck

3.Re:关于equals()方法的困惑 [Re: zmj888]	Copy to clipboard
Posted by: zmj888 Posted on: 2005-12-08 13:40 thank you

4.Re:关于equals()方法的困惑 [Re: zmj888]

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Posted by: andykid
Posted on: 2005-12-08 20:19

个人理解,黙认的equals()方法是比较引用(在java中绝大部分内置的类都重载了equals()方法，使其比较值)，在Triple1类中没有重载equals()方法，所以在System.out.println(h.equals( t ));是比较引用，显示为false,
加入红色部分的System.out.print(h=t),h和t的引用一样了。所以再接下来的
System.out.println(h==t);
显示为true,因==是比较引用。

5.Re:关于equals()方法的困惑 [Re: zmj888]	Copy to clipboard
Posted by: yangyuming Posted on: 2005-12-11 15:47 System.out.print(h=t)表示输出一个引用,因为没有重载toString方法,所以默认输出类名@标识码