自定义对象集包含相同的对象

Question

我看到了Java Set的一些奇怪行为。以下是我遇到问题的非常简单的代码片段：

public Set<StopSequence> reduce() {
    Set<StopSequence> stopSequences = new HashSet<StopSequence>();
    StopSequence currentSequence = null;

    for (StopTime stopTime: mStopTimes) {
        if (stopTime.getStopSequence() == 0) {
            //beginning of a new sequence
            if (currentSequence != null) {
                if (stopSequences.add(currentSequence)) {
                    System.out.println("Added sequence:");
                    System.out.println(currentSequence.toString());
                }   
                currentSequence.clear();
            } else {
                currentSequence = new StopSequence();
            }
            currentSequence.add(stopTime.getStopId());              
        } else {
            currentSequence.add(stopTime.getStopId());
        }
    }

    Iterator<StopSequence> iterator = stopSequences.iterator();
    while (iterator.hasNext()) {
        System.out.println(iterator.next());
    }

    return stopSequences;
}

现在看一下控制台输出，您将看到问题：

第一个System.out.println的输出，一切似乎都很好：

Added sequence: com.bviproject.gtfsobjects.StopSequence@d48dbbe6
Added sequence: com.bviproject.gtfsobjects.StopSequence@d5e1c8a1
Added sequence: com.bviproject.gtfsobjects.StopSequence@c98eb21
Added sequence: com.bviproject.gtfsobjects.StopSequence@79baf504
Added sequence: com.bviproject.gtfsobjects.StopSequence@6617f5f6
Added sequence: com.bviproject.gtfsobjects.StopSequence@7d7554ff

第二个System.out.println的输出，我的Set仅包含相同的对象。发生了什么事？

com.bviproject.gtfsobjects.StopSequence@dd017ba7
com.bviproject.gtfsobjects.StopSequence@dd017ba7
com.bviproject.gtfsobjects.StopSequence@dd017ba7
com.bviproject.gtfsobjects.StopSequence@dd017ba7
com.bviproject.gtfsobjects.StopSequence@dd017ba7
com.bviproject.gtfsobjects.StopSequence@dd017ba7
com.bviproject.gtfsobjects.StopSequence@dd017ba7
com.bviproject.gtfsobjects.StopSequence@dd017ba7