集不适用于覆盖的等于 [英] Set is not working with overridden equals

问题描述

我正在尝试使用set.所以我尝试了这种方式

I was trying to use set. so i tried this way

HashSet set=new HashSet();
Points p1 = new Points(10, 20);
Points p2 = new Points(10, 20);
System.out.println(set.add(p1)); // output true
System.out.println(set.add(p2));  // output false

我知道我的第一个输出将是true，第二个输出将是false，因为Set不允许重复的元素.而且，我也知道Set通过使用equals(Object o)方法来实现这一点.它来自具有以下签名的java Object类.

I know my first output will be true and second will be false as Set will not allow duplicate elements. And, i also know Set achieve this by using equals(Object o) method. Which comes from java Object class with following signature.

public boolean equals(Object o) {}

为了进行更深入的测试，我编写了自己的课程

For testing this little bit deeper i wrote my own class

class testSet{
    private int x;
    private int y;
    public testSet(int xa, int ya){
        this.x=xa;
        this.y=ya;
    }
    @Override
    public boolean equals(Object o){
        if (o instanceof testSet){
            testSet ts=(testSet)o;
            return ts.x==this.x && ts.y==this.y;
        }
        return false;
    }
}

现在我希望以下代码的行为与Point类相同

Now i am expecting following code will behave same as Point class

HashSet set=new HashSet();
testSet set_a=new testSet(3,4);
testSet set_b=new testSet(3,4);
System.out.println(set.add(set_a)); //output expected true
System.out.println(set.add(set_b)); //output expected false

因此，我希望第一个输出为true，第二个输出为false.但这两种情况总是返回true.但是确实为Point类工作.我尝试了以下两个Point实现

So i am expecting first output will be true and second one false . But it is always returning true for both case. But did working for Point class. And i tried with following two Point implementations

android.graphics.Point
java.awt.point 

那么我做错了什么?感谢您的帮助.

So what i did wrong? Thanks for helping guys.

推荐答案

您需要覆盖hashCode和equals. hashCode的一般约定是，如果两个对象相等(在equals的意义上)，则它们具有相同的哈希码.

You need to override hashCode as well as equals. The general contract of hashCode is that if two objects are equal (in the sense of equals), then they have the same hash code.

这篇关于集不适用于覆盖的等于的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！