java - 不被 Stream.distinct() 过滤的相等对象

Question

我有一个 Element 对象流，我需要根据相等性对其进行过滤。使用 .distinct() 似乎很容易，但我得到了异常结果。即使对象返回相等，它们也不会被 .distinct() 过滤。

我错过了什么？证明如下——

List<Element> elements = getStream().filter(e -> e.getName().equals("userId")).collect(Collectors.toList());

System.out.println("Elements with same name: " + elements.size());

if(elements.size() > 1) {
    System.out.println("Equals?: " + elements.get(0).equals(elements.get(1)));
}

System.out.println("Distinct Elements: " + getStream().distinct().count());
System.out.println("Full Elements: " + getStream().count());

输出:

Elements with same name: 2
Equals?: true
Distinct Elements: 8
Full Elements: 8

Answer 1

根据 Stream API 的 distinct() 方法(http://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#distinct--):

Returns a stream consisting of the distinct elements (according to Object.equals(Object)) of this stream.

您是否适本地覆盖了 Element 类的 equals() 和 hashCode()？

http://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#equals-java.lang.Object- http://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#hashCode--