等同于比较器的身份操作 [英] Identity operation equivalent for Comparator
问题描述
是否存在可能存在的比较器身份表示？
Is there a possible identity representation of Comparator that could exist?
在寻找简化代码的过程中在删除Java中的重载方法中，我想到了这一点，最终结论是，如果每次比较都导致对象相等，则顺序不会真正改变，从而使操作成为 identity 。因此，我最终得到了这样一个（效率低下的）建议：
In the search for simplifying the code in Removing overloaded method in Java, I thought about this and ended up concluding that if every comparison results in objects being equal, the order wouldn't really change making the operation an identity. Hence I ended up with (an inefficient) suggestion such as this:
public static <T, G> List<G> toListOfNewType(List<T> inputList, Function<T, G> mapperFunction) {
return toListOfNewType(inputList, mapperFunction, (a, b) -> 0); // overloaded with comparator for 'G' type
}
但我现在想知道的是，这对于具有自定义 compareTo 实现的对象也适用吗？在给定$ Stream 实现的情况下，真的可以肯定吗？
But what I now wonder is, would this even hold for objects with their custom compareTo implementations as well? Is it really safe to assume this given the Stream implementation?
编辑：某些我尝试过并保留顺序的测试如下：
Edit: Certain tests that I'd tried and which retained the order were as follows:
List<Integer> integers = List.of(1, 3, 45356, 47424, 34234, 4, 4, 234234, 234, 0, -23, -34);
System.out.println(integers);
System.out.println(integers.stream().sorted((a, b) -> 0).collect(Collectors.toList()));
System.out.println(integers.stream().sorted((a, b) -> 0).parallel().collect(Collectors.toList()));
[1, 3, 45356, 47424, 34234, 4, 4, 234234, 234, 0, -23, -34]
[1, 3, 45356, 47424, 34234, 4, 4, 234234, 234, 0, -23, -34]
[1, 3, 45356, 47424, 34234, 4, 4, 234234, 234, 0, -23, -34]
List<String> strings = List.of("aadad", "Z", "vsadasd", "zadad", "C", "Aadasd");
System.out.println(strings);
System.out.println(strings.stream().sorted((a, b) -> 0).collect(Collectors.toList()));
System.out.println(strings.stream().sorted((a, b) -> 0).parallel().collect(Collectors.toList()));
[aadad, Z, vsadasd, zadad, C, Aadasd]
[aadad, Z, vsadasd, zadad, C, Aadasd]
[aadad, Z, vsadasd, zadad, C, Aadasd]
Set<Integer> integerSet = Set.of(1, 3, 45356, 47424, 34234, 4, 234234, 234, 0, -23, -34);
System.out.println(integerSet);
System.out.println(integerSet.stream().sorted((a, b) -> 0).parallel().collect(Collectors.toList()));
System.out.println(integerSet.stream().sorted((a, b) -> 0).collect(Collectors.toList()));
[-34, 45356, 47424, 234, -23, 234234, 1, 34234, 3, 4, 0]
[-34, 45356, 47424, 234, -23, 234234, 1, 34234, 3, 4, 0]
[-34, 45356, 47424, 234, -23, 234234, 1, 34234, 3, 4, 0]
Set<String> stringSet = Set.of("aadad", "Z", "vsadasd", "zadad", "C", "Aadasd");
System.out.println(stringSet);
System.out.println(stringSet.stream().sorted((a, b) -> 0).collect(Collectors.toList()));
System.out.println(stringSet.stream().sorted((a, b) -> 0).parallel().collect(Collectors.toList()));
[zadad, Z, vsadasd, C, Aadasd, aadad]
[zadad, Z, vsadasd, C, Aadasd, aadad]
[zadad, Z, vsadasd, C, Aadasd, aadad]
推荐答案
对于有序流，排序是稳定。
对于无序流，没有稳定性保证。
当然，对于无序流，身份是指无论如何，排序并不是一件真正的事情，是的，常量比较器是身份顺序，因为有序流保持其顺序，而无序流保持无序。
Of course, for an unordered stream, "identity" ordering isn't really a thing anyway, so yeah, the "constant comparator" is an "identity order", in that ordered streams retain their order, and unordered streams remain unordered.
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