Equals（）结果一致，但TreeMap.containsKey（）结果不一致 [英] Consistent Equals() results, but inconsistent TreeMap.containsKey() result

问题描述

我有以下对象 Node ：

    private class Node implements Comparable<Node>(){
         private String guid();

         ...

         public boolean equals(Node o){
             return (this == o);
         }

         public int hashCode(){
              return guid.hashCode();
         }

         public int compareTo(Node o){
            return (this.hashCode() - o.hashCode());
         }

         ...

    }

然后在以下 TreeMap 中使用它：

TreeMap<Node, TreeSet<Edge>> nodes = new TreeMap<Node, TreeSet<Edge>>();

现在，树图用于名为 Graph的类来存储当前在图中的节点及其一组边缘（来自类 Edge ）。我的问题是当我尝试执行时：

Now, the tree map is used in a class called Graph to store nodes currently in the graph, along with a set of their edges (from the class Edge). My problem is when I try to execute:

   public containsNode(n){
        for (Node x : nodes.keySet()) {
            System.out.println("HASH CODE: ");
            System.out.print(x.hashCode() == n.hashCode());
            System.out.println("EQUALS: ");
            System.out.print(x.equals(n));
            System.out.println("CONTAINS: ");
            System.out.print(nodes.containsKey(n));
            System.out.println("N: " + n);
            System.out.println("X: " + x);
            System.out.println("COMPARES: ");
            System.out.println(n.compareTo(x));
            }
        }

我有时会得到以下信息：

I sometimes get the following:

哈希码：true等于：true包含：
false N：foo X：foo COMPARES：0

HASHCODE: true EQUALS: true CONTAINS: false N: foo X: foo COMPARES: 0

有人知道我在做什么错吗？我对这一切还是陌生的，所以如果我忽略了一些简单的事情，我会事先道歉（我知道 hashCode（）对<$ c $来说并不重要c> TreeMap ，但我想我会把它包括在内。）

Anyone have an idea as to what I'm doing wrong? I'm still new to all this, so I apologize in advance if I'm overlooking something simple (I know hashCode() doesn't really matter for TreeMap, but I figured I'd include it).

edit1：添加了 compareTo（）方法信息。

edit1: added compareTo() method information.

推荐答案

这里有些错误。

• 您尚未覆盖 Object.equals 。使用 @Override public boolean equals（Object obj）。


• compareTo中可能存在整数溢出错误。这可能是导致此特定错误的原因。


• compareTo 方法声称，如果哈希值相等，则两个实例相等代码碰巧匹配（可能是很难捕获的错误，如果没有代码审查）。

• You have not overriden Object.equals. Use @Override public boolean equals(Object obj).
• There is a potential integer overflow error in compareTo. This is probably the cause of this particular error. It will upset the sorting, and hence the search may well not succeed.
• The compareTo method claims two instances are equal if the hash code happens to match (could be a difficult error to catch, without code review).

有关整数溢出问题，请参见问题为什么我的简单比较器损坏了？

For integer overflow issue, see question Why is my simple comparator broken?

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