详解Java比较器

public void test1(){
    String[] arr = new String[]{"AA","BB","DD","WW","MM","PP","CC"};
    Arrays.sort(arr);
    System.out.println(Arrays.toString(arr));//[AA, BB, CC, DD, MM, PP, WW]
  }

package com.atguigu.java1;

/**
 * @author MD
 * @create 2020-07-13 15:52
 */
public class Goods implements Comparable{
  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 void setName(String name) {
    this.name = name;
  }

  public double getPrice() {
    return price;
  }

  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：按照价格的方式从小到大，再按照商品名从低到高
  @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 0;
        return this.name.compareTo(goods.name);
      }
      // 方式二：
      //return Double.compare(this.price , goods.price);
    }

    throw new RuntimeException("传入的参数不合法");

  }
}

// 测试
public void test2(){
    Goods[] arr = new Goods[4];
    arr[0] = new Goods("lx",123.12);
    arr[1] = new Goods("xm",23.12);
    arr[2] = new Goods("hw",67);
    arr[3] = new Goods("de",99);

    Arrays.sort(arr);
    System.out.println(Arrays.toString(arr));
//[Goods{name='xm', price=23.12}, Goods{name='hw', price=67.0}, Goods{name='de', price=99.0}, Goods{name='lx', price=123.12}]

  }

// 这里没有使用泛型，String已经重写了compareTo(obj)方法直接调
public void test3(){
    String[] arr = new String[]{"AA","BB","DD","WW","MM","PP","CC"};
  // 这里使用匿名
    Arrays.sort(arr, new Comparator() {

      // 安装字符串从大到小
      @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);
        }
        throw new RuntimeException("输入不合法");
      }
    });
    System.out.println(Arrays.toString(arr));//[WW, PP, MM, DD, CC, BB, AA]

  }

public void test4(){
    Goods[] arr = new Goods[4];
    arr[0] = new Goods("lx",123.1);
    arr[1] = new Goods("lx",23.12);
    arr[2] = new Goods("hw",67);
    arr[3] = new Goods("de",99);

    // 指明商品比较大小的方式，安装产品的名称从低到高排序，若名称一样，再安装价格从高到底排序
    Arrays.sort(arr, new Comparator<Goods>() {
      @Override
      public int compare(Goods o1, Goods o2) {
        if (o1.getName().equals(o2.getName())){
          return -Double.compare(o1.getPrice(),o2.getPrice());
        }else{
          return o1.getName().compareTo(o2.getName());
        }
      }
    });
    System.out.println(Arrays.toString(arr));
  //[Goods{name='de', price=99.0}, Goods{name='hw', price=67.0}, Goods{name='lx', price=123.1}, Goods{name='lx', price=23.12}]
  }