java - TreeSet.contains() 不会调用被覆盖的 equals

Question

我对 TreeSet 的 contains() 方法有问题。据我了解， contains() 应该像 javadoc 所说的那样调用包含对象的 equals() :

boolean java.util.TreeSet.contains(Object o): Returns true if this set contains the specified element. More formally, returns true if and only if this set contains an element e such that (o==null ? e==null : o.equals(e)).

我尝试做的事情:
我有一个带有成员的结果对象的 TreeSet 列表 String baseword .现在我想将每个 TreeSet 与所有其他树集进行比较，并为每对创建一个它们共享的基本词列表。为此，我为 treeSet1 遍历列表一次第二次是 treeSet2 ，然后我遍历 treeSet2 中的所有 ResultObjects并运行 treeSet1.contains(ResultObject)对于每一个，看看是否 treeSet1包含具有此词库的结果对象。我调整了 compareTo和 equals ResultObject 的方法。不过好像我的 equals永远不会被调用。
谁能解释我为什么这不起作用？

你好，
丹尼尔

    public static void getIntersection(ArrayList<TreeSet<Result>> list, int value){

          for (TreeSet<Result> treeSet : list){

    //for each treeSet, we iterate again through the list of TreeSet, starting at the TreeSet that is next
                //to the one we got in the outer loop
                for (TreeSet<Result> treeSet2 : list.subList((list.indexOf(treeSet))+1, list.size())){

                //so at this point, we got 2 different TreeSets 
                HashSet<String> intersection = new HashSet<String>();

                for (Result result : treeSet){  
                    //we iterate over each result in the first treeSet and see if the wordbase exists also in the second one                

//!!!
                    if (treeSet2.contains(result)){
                        intersection.add(result.wordbase);
                    }
                }
                if (!intersection.isEmpty()){
                    intersections.add(intersection);
                }
            }
        }


public class Result implements Comparable<Result>{

    public Result(String wordbase, double result[]){
        this.result = result;
        this.wordbase = wordbase;
    }

    public String wordbase;
    public double[] result;

    public int compareTo(DifferenceAnalysisResult o) {

        if (o == null) return 0;

        return this.wordbase.compareTo(o.wordbase);
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result
                + ((wordbase == null) ? 0 : wordbase.hashCode());
        return result;
    }

//never called
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        DifferenceAnalysisResult other = (DifferenceAnalysisResult) obj;
        if (wordbase == null) {
            if (other.wordbase != null)
                return false;
        } else if (!wordbase.equals(other.wordbase))
            return false;
        return true;
    }   
}

Answer 1

As I understand it, contains() should call equals() of the contained Objects

不适用于 TreeSet ， 不。它调用 compare :

A NavigableSet implementation based on a TreeMap. The elements are ordered using their natural ordering, or by a Comparator provided at set creation time, depending on which constructor is used.

...

Note that the ordering maintained by a set (whether or not an explicit comparator is provided) must be consistent with equals if it is to correctly implement the Set interface.

您的 compareTo方法目前与 equals 不一致- x.compareTo(null)返回 0，而 x.equals(null)返回假。也许你对此没意见，但你不应该期待 equals被称为。