HashMap的四种遍历！

HashMap的四种遍历

import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;


/**
 * Map接口:
 * 1.键值对存储一组对象
 * 2.key必须保证唯一,Value可以重复
 * 3.具体实现类:HashMap TreeMap  Hashtable   LinkedHashMap
 * HashMap 类不保证顺序
 * @author 给个赞呗!!!!!!!!!!!!!!!!!!!!!!!!!!
 * @date 2019/8/12 21:22
 */
public class Map09 {
    public static void main(String[] args){
        hashMap();
    }
    private static void hashMap(){
        Map<Integer,String> map=new HashMap<>();//Map<key,value>
        map.put(1,"HashMap");
        map.put(2,"无序的");
        map.put(3,"put方法");
        System.out.println(map.size());
        System.out.println("得到key=2的值:"+map.get(2));
        //第一种遍历 lambda表达式遍历forEach();非常简便
        map.forEach((i, s) -> System.out.println("key="+i+" 值:"+s));
        //第二种遍历  遍历Entry
        Set<Map.Entry<Integer,String>> entry=map.entrySet();
        for (Map.Entry e:entry){
            System.out.println(e.getKey()+"->"+e.getValue());
        }
        //输出entry
            System.out.println(entry);
        //第三种 遍历键 map.keySet()
        Set<Integer> key=map.keySet();
        for (Integer i:key){
            String va=map.get(i);
            System.out.println(i+"->"+va);
        }
        //第四种遍历值map.values()
        Collection<String> vs=map.values();
        for (String str:vs){
            System.out.println(str);
        }

    }
}