简介：

• 当元素的类型没有实现java.lang.Comparable接口而又不方便修改代码，或者实现了java.lang.Comparable接口的排序规则不适合当前的操作，那么可以考虑使用Comparator的对象来排序，强行对多个对象进行整体排序的比较。

• 重写compare(Object o1,Object o2)方法，比较o1和o2的大小:

  如果方法返回正整数，则表示o1大于o2; 如果返回0，表示相等; 返回负整数，表示o1小于o2。

• 可以将 Comparator传递给sort方法（如Collections.sort或Arrays.sort) ,从而允许在排序顺序上实现精确控制。

• 还可以使用Comparator来控制某些数据结构（如有序set或有序映射）的顺序，或者为那些没有自然顺序的对象collection提供排序。 ```java package mySort;

import java.util.Arrays; import java.util.Comparator;

public class CompareTest { public static void main(String[] args) { test3(); test4(); }

public static void test3() {
    String[] arr = new String[]{"AA", "VV", "MM", "GG", "BB"};
    Arrays.sort(arr, new Comparator() {
        @Override
        public int compare(Object o1, Object o2) {
            if (o1 instanceof String && o2 instanceof String) {
                String s1 = (String) o1;
                String s2 = (String) o2;
                return -s1.compareTo(s2);//实现从大到小排序
            }
            throw new RuntimeException("传入的数据类型不一致! ");
        }
    });
    System.out.println(Arrays.toString(arr));
}
public static void test4() {
    Goods[] arr = new Goods[5];
    arr[0] = new Goods("WTY1", 124);
    arr[1] = new Goods("WTY2", 24);
    arr[2] = new Goods("WTY3", 326);
    arr[3] = new Goods("WTY3", 999);
    arr[4] = new Goods("WTY4", 128);
    Arrays.sort(arr, new Comparator() {
        //指明商品比较大小的方式:
        //产品名称从低到高排序,再按照价格从高到低排序
        @Override
        public int compare(Object o1, Object o2) {
            if (o1 instanceof Goods && o2 instanceof Goods) {
                Goods g1 = (Goods) o1;
                Goods g2 = (Goods) o2;
                if (g1.getName().equals(g2.getName())) {
                    return -Double.compare(g1.getPrice(), g2.getPrice());
                } else {
                    return g1.getName().compareTo(g2.getName());
                }
            }
            throw new RuntimeException("传入的数据类型不一致! ");
        }
    });
    System.out.println(Arrays.toString(arr));
}

}

class Goods {//商品类 private String name; private double price;

public Goods() {
}
public Goods(String name, double price) {
    this.name = name;
    this.price = price;
}
public String getName() {
    return name;
}
public double getPrice() {
    return price;
}
public void setName(String name) {
    this.name = name;
}
public void setPrice(double price) {
    this.price = price;
}
@Override
public String toString() {
    return "Goods{" +
            "name='" + name + '\'' +
            ", price=" + price +
            '}';
}

}

![image.png](https://cdn.nlark.com/yuque/0/2021/png/21705001/1640265019427-235b0133-a4de-4aa0-b058-c57bf6b4b6da.png#clientId=u602e678a-3d35-4&crop=0&crop=0&crop=1&crop=1&from=paste&height=139&id=u67ec891d&margin=%5Bobject%20Object%5D&name=image.png&originHeight=139&originWidth=1366&originalType=binary&ratio=1&rotation=0&showTitle=false&size=21987&status=done&style=none&taskId=ua3118803-5f60-40a5-b8d4-5833f7cac78&title=&width=1366)
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# 案例：
```java
package mySort;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
public class DIYsort {
    public static void main(String[] args) {
        ArrayList<Shape> list = new ArrayList<>();
        Circle circle1 = new Circle(2.0);
        Circle circle2 = new Circle(3.0);
        Triangle triangle1 = new Triangle(1, 2);
        Triangle triangle2 = new Triangle(2, 2);
        list.add(circle1);
        list.add(circle2);
        list.add(triangle1);
        list.add(triangle2);
        Collections.sort(list,new MyComparator());
        System.out.println("方法一：==========================");
        list.forEach(e -> {
            System.out.println(e.getArea());
        });
        System.out.println("方法二：==========================");
        new testt().bj();
    }
}
class MyComparator implements Comparator<Shape> {
    @Override
    public int compare(Shape o1, Shape o2) {//升序排序
        return Double.compare(o1.getArea(),o2.getArea());
    }
}
class testt implements Comparator<Shape>{
    public void bj(){
        ArrayList<Shape> list = new ArrayList<>();
        Circle circle1 = new Circle(2.0);
        Circle circle2 = new Circle(3.0);
        Triangle triangle1 = new Triangle(1, 2);
        Triangle triangle2 = new Triangle(2, 2);
        list.add(circle1);
        list.add(circle2);
        list.add(triangle1);
        list.add(triangle2);
        Collections.sort(list,new testt());
        list.forEach(e -> {
            System.out.println(e.getArea());
        });
    }
    @Override
    public int compare(Shape o1, Shape o2) {//降序排序
        return -Double.compare(o1.getArea(),o2.getArea());
    }
}
interface Shape{
    double getArea();
}
class Circle implements Shape{
    private double r;
    public Circle() {
    }
    public Circle(double r) {
        this.r = r;
    }
    @Override
    public double getArea() {
        return Math.PI * r * r;
    }
}
class Triangle implements Shape {
    private double length;
    private double width;
    public Triangle() {
    }
    public Triangle(double length, double width) {
        this.length = length;
        this.width = width;
    }
    @Override
    public double getArea() {
        return length * width;
    }
}