请指教下，刚开始看java

[Crystal辰]

我昨天看了个Map集合的例子，然后自己写了下，但是怎么遍历的时候只有输出3个，put方法然道没put进去？代码如下

import java.util.*;
public class PropTest{
	public static void main(String[] args){
		Product p1 = new Product("西瓜",1.0);
		Product p2 = new Product("桃子",6.0);
		Product p3 = new Product("苹果",4.0);
		Product p4 = new Product("草莓",2.0);
		Product p5 = new Product("樱桃",12.0);
		
		SortedMap pr = new TreeMap();
		pr.put(p1,"10kg");
		pr.put(p2,"20kg");
		pr.put(p3,"11kg");
		pr.put(p4,"13kg");
		pr.put(p5,"14kg");

		System.out.println(pr.size());
	         Set s = pr.keySet();
		Iterator it = s.iterator();
		 
		while(it.hasNext()){
			Object o1 = it.next();
			Object v = pr.get(o1);
			System.out.println("key:"+o1+",value:"+v);
			}
		}
	}
	
class Product implements Comparable{
	String name;
	double price;
	Product(String name,double price){
		this.name = name;
		this.price = price;
		}
	public String toString(){
		return "[name:"+name+"  price:"+price+"]";
		}
	public int compareTo(Object o){
			Product o1 = (Product)o;
		double price1 = this.price;
		double price2 = o1.price;
		if(price1>price2){
			return 1;
		}else if(price1>price2){
			return -1;
			}else return 0;
		}
	}

[LCore]

引用 楼主 lizhipeng777 的回复:

我昨天看了个Map集合的例子，然后自己写了下，但是怎么遍历的时候只有输出3个，put方法然道没put进去？代码如下

import java.util.*;
public class PropTest{
	public static void main(String[] args){
		Product p1 = new Product("西瓜",1.0);
		Product p2 = new Product("桃子",6.0);
		Product p3 = new Product("苹果",4.0);
		Product p4 = new Product("草莓",2.0);
		Product p5 = new Product("樱桃",12.0);
		
		SortedMap pr = new TreeMap();
		pr.put(p1,"10kg");
		pr.put(p2,"20kg");
		pr.put(p3,"11kg");
		pr.put(p4,"13kg");
		pr.put(p5,"14kg");

		System.out.println(pr.size());
	         Set s = pr.keySet();
		Iterator it = s.iterator();
		 
		while(it.hasNext()){
			Object o1 = it.next();
			Object v = pr.get(o1);
			System.out.println("key:"+o1+",value:"+v);
			}
		}
	}
	
class Product implements Comparable{
	String name;
	double price;
	Product(String name,double price){
		this.name = name;
		this.price = price;
		}
	public String toString(){
		return "[name:"+name+"  price:"+price+"]";
		}
	public int compareTo(Object o){
			Product o1 = (Product)o;
		double price1 = this.price;
		double price2 = o1.price;
		if(price1>price2){
			return 1;
		}else if(price1>price2){
			return -1;
			}else return 0;
		}
	}

楼主要仔细了，class Product implements Comparable 实现的compareTo方法逻辑问题！

else if(price1>price2){
			return -1;
			}else return 0;
		}

改成price1<price2

[菖蒲老先生]

要细心啊。。。。 } else if (price1 < price2) {

[StevenLoveMaggie]

引用 1 楼 kiritor 的回复:

[quote=引用 楼主 lizhipeng777 的回复:] 我昨天看了个Map集合的例子，然后自己写了下，但是怎么遍历的时候只有输出3个，put方法然道没put进去？代码如下

import java.util.*;
public class PropTest{
	public static void main(String[] args){
		Product p1 = new Product("西瓜",1.0);
		Product p2 = new Product("桃子",6.0);
		Product p3 = new Product("苹果",4.0);
		Product p4 = new Product("草莓",2.0);
		Product p5 = new Product("樱桃",12.0);
		
		SortedMap pr = new TreeMap();
		pr.put(p1,"10kg");
		pr.put(p2,"20kg");
		pr.put(p3,"11kg");
		pr.put(p4,"13kg");
		pr.put(p5,"14kg");

		System.out.println(pr.size());
	         Set s = pr.keySet();
		Iterator it = s.iterator();
		 
		while(it.hasNext()){
			Object o1 = it.next();
			Object v = pr.get(o1);
			System.out.println("key:"+o1+",value:"+v);
			}
		}
	}
	
class Product implements Comparable{
	String name;
	double price;
	Product(String name,double price){
		this.name = name;
		this.price = price;
		}
	public String toString(){
		return "[name:"+name+"  price:"+price+"]";
		}
	public int compareTo(Object o){
			Product o1 = (Product)o;
		double price1 = this.price;
		double price2 = o1.price;
		if(price1>price2){
			return 1;
		}else if(price1>price2){
			return -1;
			}else return 0;
		}
	}

楼主要仔细了，class Product implements Comparable 实现的compareTo方法逻辑问题！

else if(price1>price2){
			return -1;
			}else return 0;
		}

改成price1<price2[/quote] 同意楼上，楼主要注意啦！

[TheNowWjj]

帅哥，compareTo 方法 else if 条件错了。应该是小宇。

[Crystal辰]

引用 1 楼 kiritor 的回复:

[quote=引用 楼主 lizhipeng777 的回复:] 我昨天看了个Map集合的例子，然后自己写了下，但是怎么遍历的时候只有输出3个，put方法然道没put进去？代码如下

import java.util.*;
public class PropTest{
	public static void main(String[] args){
		Product p1 = new Product("西瓜",1.0);
		Product p2 = new Product("桃子",6.0);
		Product p3 = new Product("苹果",4.0);
		Product p4 = new Product("草莓",2.0);
		Product p5 = new Product("樱桃",12.0);
		
		SortedMap pr = new TreeMap();
		pr.put(p1,"10kg");
		pr.put(p2,"20kg");
		pr.put(p3,"11kg");
		pr.put(p4,"13kg");
		pr.put(p5,"14kg");

		System.out.println(pr.size());
	         Set s = pr.keySet();
		Iterator it = s.iterator();
		 
		while(it.hasNext()){
			Object o1 = it.next();
			Object v = pr.get(o1);
			System.out.println("key:"+o1+",value:"+v);
			}
		}
	}
	
class Product implements Comparable{
	String name;
	double price;
	Product(String name,double price){
		this.name = name;
		this.price = price;
		}
	public String toString(){
		return "[name:"+name+"  price:"+price+"]";
		}
	public int compareTo(Object o){
			Product o1 = (Product)o;
		double price1 = this.price;
		double price2 = o1.price;
		if(price1>price2){
			return 1;
		}else if(price1>price2){
			return -1;
			}else return 0;
		}
	}

楼主要仔细了，class Product implements Comparable 实现的compareTo方法逻辑问题！

else if(price1>price2){
			return -1;
			}else return 0;
		}

改成price1<price2[/quote] 好吧，我承认我粗心了，没去仔细检查，多谢！

[dracularking]

TreeMap不是用equals来判断key是否相同，而是用compareTo，这样一来，不大于的都变成等于了，执行了替换

[地下室森林]

首先看api：

基于红黑树（Red-Black tree）的 NavigableMap 实现。
该映射根据其键的自然顺序进行排序，或者根据创建映射时提供的
 Comparator 进行排序，具体取决于使用的构造方法。

1. 你题目要想显示5的话改下价钱就行，你把价钱改成都大于前面那个数的话。 2. 但是真正的地方还是你的comparable里面的compareto方法设定的出错。直接如下：

return (int) (o1.price - o2.price);

这样的话如果两个product价格一样的话只会显示一个。因为返回 0 。