java - 是否可以使用 Comparator.comparingInt 链按两个字段以相反的自然顺序对对象进行排序

Question

假设我想以相反的顺序对字段 height 上的 ArrayList 中的对象进行排序，如果两个值相同，我想进一步对字段宽度进行排序也以相反的顺序。 有没有办法使用类似

的东西

 Comparator<Test> comparator = Comparator
            .comparingInt((Test t) -> t.height).reversed()
            .thenComparingInt((Test t ) -> t.width).reversed();

我知道我可以使用类似的东西:

Collections.sort(list, new Comparator<Test>() {

        public int compare(Test o1, Test o2) {

            Integer x1 =  o1.height;
            Integer x2 =  o2.height;
            int sComp = x2.compareTo(x1);

            if (sComp != 0) {
                return sComp;
            }

            x1 = o1.width;
            x2 = o2.width;
            return x2.compareTo(x1);
        }});

但是我真的很好奇是否有一条线解决方案

所以关于这个小例子

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;

public class Main {

    public static void main(String[] args) {
        Test one = new Test();
        one.height = 2;
        one.width = 1;
        Test two = new Test();
        two.height = 2;
        two.width = 3;
        Test three = new Test();
        three.height = 1;
        three.width = 1;

        Comparator<Test> comparator = Comparator
            .comparingInt((Test t) -> t.height).reversed()
            .thenComparingInt((Test t ) -> t.width).reversed();

        List<Test> list = new ArrayList<>();
        list.add(one);
        list.add(two);
        list.add(three);

        list.stream()
            .sorted(comparator)
            .forEach(e -> System.out.println(e.height + "/" + e.width));
    }
}

class Test {
    int width;
    int height;
}

我得到输出:

1/1
2/3
2/1

因为第二个 reversed() 反转了整个列表。 有没有办法生成以下输出:

2/3
2/1
1/1

Answer 1

只需从 comparingInt 中删除 reversed() 并仅在 thenComparingLong 上调用 reversed:

Comparator<Test> comparator = 
      Comparator.comparingInt((Test t) -> t.height) // <--- removed reverse from this comparator
                .thenComparingLong((Test t ) -> t.width).reversed();

此外，鉴于 width 是一个 int，我将使用 thenComparingInt 而不是 thenComparingLong。

此外，关于流管道，我建议使用 forEachOrdered，因为您关心元素打印的顺序。

forEach 记录为:

The behavior of this operation is explicitly nondeterministic. For parallel stream pipelines, this operation does not guarantee to respect the encounter order of the stream, as doing so would sacrifice the benefit of parallelism.

因此:

 list.stream()
     .sorted(comparator)
     .forEachOrdered(e -> System.out.println(e.height + "/" + e.width));