自然排序

package mySort;
import java.util.Arrays;
public class CompareTest {
    public static void main(String[] args) {
        test1();
        test2();
    }
    /**
    ComparabLe接口的使用举例: 自然排序
     1.像String、包装类等实现了Comparable接口，重写了compareTo()方法，给出了两个对象大小的比较方式
     2.像String、包装类重写compareTo()方法以后，进行了从小到大的排列
     3.重写compareTo(obj)的规则:
     如果当前对象this大于形参对象obj，则返回正整数，
     如果当前对象this小于形参对象obj，则返回负整数，
     如果当前对象this等于形参对象obj，则返回零。
     4.对于自定义类来说，如果需要排序，我们可以让自定义类实现Comparable接口，重写了compareTo()方法。
        需要在compareTo(obj)方法中指明如何排序
     */
    public static void test1(){
        String[] arr = new String[]{"AA","VV","MM","GG","BB"};
        Arrays.sort(arr);
        System.out.println(Arrays.toString(arr));
    }
    public static void test2(){
        Goods[] arr = new Goods[4];
        arr[0] = new Goods("WTY1",124);
        arr[1] = new Goods("WTY2",24);
        arr[2] = new Goods("WTY3",326);
        arr[3] = new Goods("WTY4",128);
        Arrays.sort(arr);
        System.out.println(Arrays.toString(arr));
    }
}
class Goods implements Comparable{//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 +
                '}';
    }
    //指明商品比较大小的方式:
    //价格从低到高排序,再按照产品名称从高到低排序
    @Override
    public int compareTo(Object o) {
        if(o instanceof Goods){
            Goods goods = (Goods) o;
            //方式一：
            if(this.price > goods.price){
                return 1;
            }else if(this.price < goods.price){
                return -1;
            }else {
                return -this.name.compareTo(goods.name);//前面加了一个负号
            }
            //方式二：
            //return Double.compare(this.price,goods.price);
        }
        throw new RuntimeException("传入的数据类型不一致! ");
    }
}

package mySort;
import java.util.ArrayList;
import java.util.Collections;
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);
        list.forEach(e -> {
            System.out.println(e.getArea());
        });
    }
}
interface Shape extends Comparable<Shape>{
    double getArea();
    @Override
    int compareTo(Shape o);
}
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;
    }
    @Override
    public int compareTo(Shape o) {
        Double a1 = getArea();
        Double a2 = o.getArea();
        return a1.compareTo(a2);
    }
}
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;
    }
    @Override
    public int compareTo(Shape o) {
        Double a1 = getArea();
        Double a2 = o.getArea();
        return a1.compareTo(a2);
    }
}