hashmap笔记

hashmap用法笔记

package com.app;

import java.util.HashMap;
import java.util.Iterator;

public class app {

    /**
     * @param args
*/
    public static void main(String[] args) {
        // TODO Auto-generated method stub    
        HashMap<String, Double> map = new HashMap<String, Double> ();
        
        map.put("hello", 1.0);
        map.put("fine", 2.0);
        map.put("suck", 3.0);
        
        Iterator<String>  it = map.keySet().iterator();
        
        if(map.containsKey("why")){
            System.out.println("Key why exist");
        }
        
        if(map.containsValue(2.0)){
            System.out.println("Value 2 exist");
        }
        
        /***Hash的遍历***/
        if(!map.isEmpty()){
            while(it.hasNext()){
                String tempKey = it.next();
                if(tempKey.equals("fine")){
                    Double tempValue = map.get(tempKey) + 10;
                    map.put(tempKey, tempValue);
                    
                    System.out.println("fine is update to " + tempValue);
                }else{
                    System.out.println(map.get(tempKey));
                }            
            }
        }else{
            System.out.println("map is empty");
        }
        
        map.clear();
        
        if(map.isEmpty()){
            System.out.println("map is empty");
        }
    }
}

hashmap的排序：

package com.app;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class app {

    /**
     * @param args
*/
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Map<String, Integer> map = new HashMap<String, Integer>();
        map.put("hello", 1);
        map.put("fine", 3);
        map.put("abandon", 2);
        
        List<Map.Entry<String, Integer>> list = 
            new ArrayList<Map.Entry<String, Integer>>(map.entrySet());
        
        for(int i = 0; i < list.size(); i++){
            String id = list.get(i).getKey();
            System.out.println(id);
        }
        
        Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
            public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2){
                return (o1.getKey()).toString().compareTo(o2.getKey());
            }//String类的compareTo方法实现字典排序
        });
        
        for(int i = 0; i < list.size(); i++){
            String id = list.get(i).getKey();
            System.out.println(id);
        }    
    }
}