Java ArrayList Contain 尽管包含相同的值，但它始终返回 false [英] Java ArrayList Contain always return false although it contain the same value

问题描述

这是我的空位课程

class Hole {

public  int a;
public  int b;

Hole(int a, int b) {
    this.a = a;
    this.b = b;
}

所以我添加了一个包含几个洞的 ArrayList

So i adding an ArrayList that contain several several hole

public void checkPathLoop(int x, int y) {
        //rough code

        ArrayList<Hole> leftFlowInnerHole = new ArrayList<>();


        //left holes rules
        leftFlowInnerHole.add(new Hole(0, 1));
        leftFlowInnerHole.add(new Hole(1, 5));
        leftFlowInnerHole.add(new Hole(5, 4));
        leftFlowInnerHole.add(new Hole(0, 4));

当我添加

Hole userInputHole = new Hole(0,1);
System.out.print(leftFlowInnerHole.contain(userInputHole));

它总是返回 false ！！它假设返回true.

it always return false !! it suppose to return true.

有什么我想念的吗??

提前致谢

推荐答案

您需要重写从 Object 类继承的 equals 方法(因此也是 hashCode 遵守合约，见 为什么我需要在您的 Hole 类中覆盖 Java 中的 equals 和 hashCode 方法?).

You need to override the equals method herited from the Object class (and hence also hashCode to respect the contract, see Why do I need to override the equals and hashCode methods in Java? ) in your Hole class.

如果此列表包含指定的元素，则返回 true.更多的形式上，当且仅当此列表包含至少一个时返回 true元素 e 使得 (o==null ? e==null : o.equals(e)).

Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).

基本上默认的 equals 实现是两个对象之间的 == 比较

Basically the default equals implementation is an == comparison between the two objects

public boolean equals(Object obj) {
   return (this == obj);
}

由于您创建了两个不同的对象，虽然它们具有与属性相同的值，但它们是两个不同的对象，因此 this == obj 返回 false.

Since you created two different objects, while they have the same value as attributes they're two distincts objects and hence this == obj returns false.

如果你这样做了:

Hole a = new Hole(0,1);
leftFlowInnerHole.add(a);
System.out.print(leftFlowInnerHole.contains(a));

你会看到它输出 true.

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