java 中的map

map初始容量是16

package com.tedu.study01;

import java.util.HashMap;
import java.util.Map;

public class study_Map {
    public static void main(String[] args) {
        // 创建一个map集合
        Map<String,String > map = new HashMap<>();
        // 在集合中存储元素
        map.put("name","胡国");
        map.put("age","18");
        map.put("addr","北京");
        map.put("name2","姜育恒");
        System.out.println(map);
        System.out.println(map.get("addr"));
        System.out.println(map.remove("addr"));
        System.out.println(map);
        System.out.println(map.keySet());
    }
}

综合map实例

package com.tedu.study01;

import java.util.*;

public class study_Map {
    public static void main(String[] args) {
        // 创建一个map集合
        Map<String,String > map = new HashMap<>();
        // 在集合中存储元素
        map.put("name","胡国");
        map.put("age","18");
        map.put("addr","北京");
        map.put("name2","姜育恒");
        System.out.println(map);
        System.out.println(map.get("addr"));
        System.out.println(map.remove("addr"));
        System.out.println(map);
        System.out.println(map.keySet());
        System.out.println(map.values());
        // 将map集合转换成set，通过keyset方法
        Set<String> keySet = map.keySet();
        for (String key :
                keySet) {
            System.out.println(key+":"+map.get(key));
        }
        System.out.println("===========================");
        //方式二 将map集合转换成set集合,通过entrySet（）将map转换成set
        Set<Map.Entry<String,String>> entrySet = map.entrySet();
        for (Map.Entry<String, String> entry :
                entrySet) {
            System.out.println(entry.getKey()+":"+entry.getValue());
        }
        System.out.println("====================================");
        // 将map转换成collection集合，通过values方法获取value
        Collection<String> values = map.values();
        for (String a :
                values) {
            // 可以 通过key获取value，不能通过value获取key
            System.out.println(a);
        }
        // 方式四
        System.out.println("=======++++++++++++++++++++++++++++++++++++++++++++++++");
        Set<Map.Entry<String,String>> entrySet2 = map.entrySet();
        Iterator<Map.Entry<String, String>> iterator = entrySet2.iterator();
        while (iterator.hasNext()){
            Map.Entry<String,String> entry = iterator.next();
            System.out.println(entry.getKey()+":"+entry.getValue());
        }
    }

}