Comparable接口比较排序 示例

Posted 2020-08-11

package cn.caijiajia.campaignnew.job;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class Book implements Comparable{
    /*编写一个类Book，具有name,price,press,author属性.然后创建5个对象放入ArrayList中，并实现按照price大小排序（使用Comparable接口排序），
       然后遍历ArrayList输出每个Book对象。*/
    private String name;
    private float price;
    private String press;
    private String author;
    private int id;

    //构造方法
    public Book(String name,float price,String press,String author,int id){
        this.name = name;
        this.price = price;
        this.press = press;
        this.author = author;
        this.id = id;
        System.out.println(name.toString());
    }
    @SuppressWarnings("unchecked")
    public static void main(String[] args){
        List<Book> list = new ArrayList<Book>();
        Book b1=new Book("java1",25f,"不错的书","LY1",1);
        Book b2=new Book("java2",30f,"不错的书","LY2",2);
        Book b3=new Book("java3",30f,"不错的书","LY2",3);
        Book b4=new Book("java4",30f,"不错的书","LY2",4);
        Book b5=new Book("java5",80f,"不错的书","LY3",5);
        Book b6=new Book("java6",40f,"不错的书","LY4",6);
        Book b7=new Book("java7",15f,"不错的书","LY5",7);
        list.add(b1);
        list.add(b2);
        list.add(b3);
        list.add(b4);
        list.add(b5);
        list.add(b6);
        list.add(b7);

//.sort(List)方法,当然还可能使用java.util.Arrays.sort(数组),那样就必须把
//list转化为数组,由于本例使用Collections.sort(List)已经足够,另一方法,大家可//以尝试自已使用.

        Collections.sort(list);

        for(int i=0;i<list.size();i++){
            Book book = (Book)list.get(i);
            System.out.println(book);
        }
    }
    //重写Comparable接口方法
    public int compareTo(Object obj) {
        Book p = (Book)obj;
        //按价格降序
        if(p.price>this.price){
            return 1;
        }
        else if(p.price<this.price){
            return -1;
        }
        else{
            //价格相同按id降序（默认是升序）
            if(p.id<this.id)
                return -1;
            else if(p.id>this.id)
                return 1;
            else
                return 0;
        }
    }
    //重写toString方法
    public String toString(){//这上是重写了本类的toString方法,对系统自带的其它字段的toString方法无效
        return "书名："+this.name+", 价格："+this.price+", 说明："+this.press+", 作者: "+this.author+", id: "+this.id;
    }
}