Java集合-----Map详解

package com.gather;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;

public class HashMapPractise {
    public static void main(String[] args) {
        Map<String, Person> map = new HashMap<>();
        Person p1 = new Person("张三", 22);
        Person p2 = new Person("李四", 23);
        Person p3 = new Person("王五", 22);
        map.put("AA", p1);
        map.put("BB", p2);
        map.put("CC", p3);
        
        //第一种遍历方式：能同时取出键值对
        for(String str:map.keySet()) {
           System.out.println("键为:"+str+",值为:"+map.get(str));
        }
        System.out.println("------------------------------");
        
        //第二种遍历方式：只取值或只取键
        for(String str:map.keySet()) {
            System.out.println("键为:"+str);
        }
        
        for(Person person:map.values()) {
            System.out.println("值为:"+person);
        }
        System.out.println("------------------------------");
        
        //推荐：第三种遍历方式：能同时取出键值对
        for(Entry<String,Person> entry:map.entrySet()) {
            System.out.println("键为:"+entry.getKey()+",值为:"+entry.getValue());
        }
        System.out.println("------------------------------");
        
        //第四种遍历方式：能同时取出键值对
        Iterator<Entry<String, Person>> entries = map.entrySet().iterator(); 
        while (entries.hasNext()) { 
            Entry<String, Person> entry = entries.next(); 
            System.out.println("键为:"+entry.getKey()+",值为:"+entry.getValue()); 
        }
    }
}

package com.gather;

import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Map;
import java.util.Map.Entry;

public class HashtablePractise {
    public static void main(String[] args) {
        Map<String, Person> map = new Hashtable<>();
        Person p1 = new Person("张三", 22);
        Person p2 = new Person("李四", 23);
        map.put("AA", p1);
        map.put("BB", p2);

        for (Entry<String, Person> entry : map.entrySet()) {
            System.out.println("键为:" + entry.getKey() + ",值为:" + entry.getValue());
        }
        System.out.println("------------------------------");

        Hashtable<String, Person> hashtable = new Hashtable<>();
        hashtable.put("AA", p1);
        hashtable.put("BB", p2);

        // Hashtable的另外一种遍历方式：Enumeration
        Enumeration<String> enuKey = hashtable.keys();
        while (enuKey.hasMoreElements()) {
            System.out.println(enuKey.nextElement());
        }

        Enumeration<Person> enuValue = hashtable.elements();
        while (enuValue.hasMoreElements()) {
            System.out.println(enuValue.nextElement());
        }
    }
}