java8 按复数key将list排序

Java8中可以使用`Comparator`和`Map.Entry`来对具有复数键的`Map`进行排序，可以按照键的实部或虚部进行排序。

以下是一个示例代码：

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        Map<ComplexNumber, String> map = new HashMap<>();
        map.put(new ComplexNumber(3, 2), "a");
        map.put(new ComplexNumber(1, 4), "b");
        map.put(new ComplexNumber(2, 3), "c");

        // 按键的实部排序
        List<Map.Entry<ComplexNumber, String>> entries1 = map.entrySet()
                .stream()
                .sorted(Comparator.comparing(e -> e.getKey().getReal()))
                .collect(Collectors.toList());

        // 按键的虚部排序
        List<Map.Entry<ComplexNumber, String>> entries2 = map.entrySet()
                .stream()
                .sorted(Comparator.comparing(e -> e.getKey().getImaginary()))
                .collect(Collectors.toList());

        System.out.println("按键的实部排序：");
        for (Map.Entry<ComplexNumber, String> entry : entries1) {
            System.out.println("key=" + entry.getKey() + ", value=" + entry.getValue());
        }

        System.out.println("按键的虚部排序：");
        for (Map.Entry<ComplexNumber, String> entry : entries2) {
            System.out.println("key=" + entry.getKey() + ", value=" + entry.getValue());
        }
    }
}

class ComplexNumber {
    private double real;
    private double imaginary;

    public ComplexNumber(double real, double imaginary) {
        this.real = real;
        this.imaginary = imaginary;
    }

    public double getReal() {
        return real;
    }

    public void setReal(double real) {
        this.real = real;
    }

    public double getImaginary() {
        return imaginary;
    }

    public void setImaginary(double imaginary) {
        this.imaginary = imaginary;
    }

    @Override
    public String toString() {
        return real + "+" + imaginary + "i";
    }
}

输出结果：

按键的实部排序：
key=1.0+4.0i, value=b
key=2.0+3.0i, value=c
key=3.0+2.0i, value=a
按键的虚部排序：
key=3.0+2.0i, value=a
key=2.0+3.0i, value=c
key=1.0+4.0i, value=b