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如何编写比较多个参数的比较器[[副本]

comparator comparison java

onCC · 技术社区 · 7 年前

public class Coordinate {

    private int x, y;

    public Coordinate(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getY() {
        return y;
    }

    public void setY(int y) {
        this.y = y;
    }

}

现在我想让比较器比较类坐标的两个实例的x和y值。举个例子:
我有一个坐标c1,它有x=42和y=23。我的第二个坐标c2有x=23和y=54。现在我把它们都放在一个数组列表中,我想对列表进行排序。我想按以下方式分类:
y值最小的坐标总是第一个,当有两个y值相同的坐标时,x值较低的坐标总是第一个。

c1 (y = 4, x = 5 ) < c2 (y = 4, x = 6) < c3 (y = 5, x = 2)

那么我怎样才能写一个比较器来达到这个目的呢?
非常感谢你!

2 回复 | 直到 7 年前

Andrew 7 年前

Comparator<Coordinate> c = Comparator.comparingInt(Coordinate::getY)
                                     .thenComparingInt(Coordinate::getX);

thenComparing 和 thenComparingX .

var list = List.of(
        new Coordinate(6, 4),
        new Coordinate(2, 5),
        new Coordinate(5, 4)
);

list.sort(c);
System.out.println(list);

片段打印出来

[{y=4, x=5}, {y=4, x=6}, {y=5, x=2}]

shirish 7 年前

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

class Coordinate {
    private int x, y;

    public Coordinate(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getY() {
        return y;
    }

    public void setY(int y) {
        this.y = y;
    }

    public String toString() {
        return "x = " + x + " y = " + y;
    }
}

public class Temp {
    public static void main(String[] args) {
        ArrayList<Coordinate> A = new ArrayList<>();
        A.add(new Coordinate(1, 2));
        A.add(new Coordinate(2, 1));
        A.add(new Coordinate(3, 2));
        A.sort(new Comparator<Coordinate>() {

            @Override
            public int compare(Coordinate o1, Coordinate o2) {
                if (o1.getY() < o2.getY()) {
                    return -1;
                } else if (o1.getY() > o2.getY()) {
                    return 1;
                } else {
                    if (o1.getX() < o2.getX()) {
                        return -1;
                    } else if (o1.getX() > o2.getX()) {
                        return 1;
                    }
                    return 0;
                }
            }
        });
        System.out.println(A.toString());
    }
}

使用可比接口

import java.util.ArrayList;

class Coordinate implements Comparable<Coordinate> { # Notice implementing Comparable interface
    private int x, y;

    public Coordinate(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public int getX() {
        return x;
    }

    public void setX(int x) {
        this.x = x;
    }

    public int getY() {
        return y;
    }

    public void setY(int y) {
        this.y = y;
    }

    @Override
    public int compareTo(Coordinate o) { # implementing the abstract method of Comparable interface
        if (y < o.y) {
            return -1; 
        } else if (y > o.y) {
            return 1;
        } else {
            if (x < o.x) {
                return -1;
            } else if (x > o.x) {
                return 1;
            }
            return 0;
        }
    }

    public String toString() {
        return "x = " + x + " y = " + y;
    }
}

public class Temp {
    public static void main(String[] args) {
        ArrayList<Coordinate> A = new ArrayList<>();
        A.add(new Coordinate(1, 2));
        A.add(new Coordinate(2, 1));
        A.add(new Coordinate(3, 2));
        A.sort(null);
        System.out.println(A.toString());
    }
}

输出

[x = 2 y = 1, x = 1 y = 2, x = 3 y = 2]