//模拟商品包含编号、名称、价格、产地、生产日期等详细信息

import java.util.Date;



public class Product implements Comparable<Product>{

	private	int id;	//商品编号；

	private String name;	//商品名称；

	private double price;	//价格

	private String place;	//商品产地；

	private Date	date;	//生产日期

	//无参构造方法

	public Product(){super();}

	//有参构造方法

	public Product(int id,String name,double price,String place,Date date){

		super();

		this.id=id;

		this.name=name;

		this.place=place;

		this.date=date;

	}

	public int getId(){

		return id;

	}

	public void setId(int id){

		this.id=id;

	}

	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;

	}

	public String getPlace(){

		return place;

	}

	public void setPlace(String place){

		this.place=place;

	}

	public Date getDate(){

		return date;

	}

	public void setDate(Date date){

		this.date=date;

	}

//	public int compare(Object obj1,Object obj2){

//		Product p1=(Product)obj1;

//		Product p2=(Product)obj2;

//		if(p1.getName().compareTo(p2.getName())>0)

//			return -1;

//		if(p1.getName().compareTo(p2.getName())<0)

//			return 1;

//		return 0;

//	}

	public int compareTo(Product p){

		if(this.getId()>p.getId()){

			return -1;

		}else if(this.getId()<p.getId()){

			return 1;

		}else{

			return 0;

		}

	}

}import java.util.Date;

import java.util.Iterator;

import java.util.Set;

import java.util.TreeSet;





public class CompareProduct {

	public static void main(String[] args) {

		//创建Set对象，传入一个参数比较器

		Set set=new TreeSet<Product>();

		Product water=new Product(1001,"柯蓝村井水",1.5,"郑州",new Date());

		Product cocacola=new Product(1002,"可口可乐",2.5,"郑州太古可乐",new Date());

		Product book=new Product(1003,"货币战争",66,"北京大兴中信出版社",new Date());

		Product pen=new Product(1004,"钢笔",100,"上海",new Date());

		set.add(water);

		set.add(pen);

		set.add(book);

		set.add(cocacola);

		System.out.println(set);

		//使用迭代输出集合对象；

//		Iterator it=set.iterator();

//		while(it.hasNext()){

//			Product p=(Product)it.next();

//			System.out.println(p.getName()+"--"+p.getPrice());

//		}

	}

}

，显示[Product@e53108, Product@f62373, Product@19189e1, Product@1f33675]

，为什么不显示元素内容呢？