HashSet似乎没有意识到两个对象是相同的. [英] HashSet does not seem to realize that two objects are the same.

问题描述

我试图使用HashSet来存储我创建的类的对象，但是显然相同的对象似乎具有两个不同的哈希，这就是为什么contains方法没有意识到该对象已经在HashSet中的原因.这导致我的程序用尽了堆内存.

I'm trying to use HashSet to store objects of a class that I created, but apparently the same objects seem to have two different hashes, which is why the contains method does not realize that the object is already in the HashSet. This leads to my program running out of heap memory.

我认为我没有做错任何事情，但是无论如何我都希望有第二意见.我已经做过类似的操作，但是一切都很好，这使它特别烦人.我将不胜感激.

I don't think I'm doing anything wrong, but I wanted a second opinion anyway. I've done similar operations before which all worked fine, which makes this particularly annoying. I'd appreciate any help.

这是我的代码

move1 = new Move(t,s);
if(move1.hashCode()==new Move(t,s).hashCode())
    System.out.println("match");
move2 = new Move(s,t);
moves.add(move1); 
moves.add(move2);
if(moves.contains(new Move(t,s)))
    System.out.println("match found");

这里是Move类:

public class Move {
    private int move1;
    private int move2;

    Move(int m1, int m2)
    {
        move1 = m1;
        move2 = m2;
    }

    public String toString()
    {
         return String.valueOf(move1)+" "+String.valueOf(move2);
    }
}

这是我得到的输出

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
    at java.util.HashMap.addEntry(HashMap.java:797)
    at java.util.HashMap.put(HashMap.java:431)
    at java.util.HashSet.add(HashSet.java:194)
    at makeMove.<init>(makeMove.java:33)

推荐答案

您需要覆盖

You need to override the Object#hashCode() method in the Move class to let it return the same hashCode() value for the state of the Move instance. Don't forget to override Object#equals() as well.

• 在Java中覆盖等号和hashCode

提示:如果您使用的是类似 Eclipse 的IDE，则可以也只是自动生成它们.右键单击Move类的某个位置，然后选择 Source>生成hashCode()和equals().如下所示:

Hint: if you're using an IDE like Eclipse, you can also just autogenerate them. Rightclick somewhere the Move class, choose Source > Generate hashCode() and equals(). Here is how it look like then:

@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + move1;
    result = prime * result + move2;
    return result;
}

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Move other = (Move) obj;
    if (move1 != other.move1)
        return false;
    if (move2 != other.move2)
        return false;
    return true;
}

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