Java中HashMap遍历的四种方式

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package bean;

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

public class HashMapDemo
{
    public static void main(String[] args)
    {
        Map<String, String> map = new HashMap<String, String>();
        map.put("name", "张三");
        map.put("gender", "男");
        map.put("age", "23");
        map.put("address", "北京");

        // 1、keySet()+for循环方式，遍历两次，效率低
        for (String key : map.keySet())
        {
            System.out.println(key + "," + map.get(key));
        }

        // 2、entrySet()+for循环方式，遍历一次，效率高（推荐使用）
        for (Entry<String, String> entry : map.entrySet())
        {
            System.out.println(entry.getKey() + "," + entry.getValue());
        }

        // 3、keySet()+Iterator遍历，遍历两次，效率低
        Set<String> set = map.keySet();
        Iterator<String> iterator = set.iterator();
        while (iterator.hasNext())
        {
            String key = iterator.next();
            System.out.println(key + "," + map.get(key));
        }

        // 4、entrySet()+Iterator遍历，遍历一次，效率高（推荐使用）
        Set<Entry<String, String>> set = map.entrySet();
        Iterator<Entry<String, String>> iterator = set.iterator();
        while (iterator.hasNext())
        {
            Entry<String, String> entry = iterator.next();
            System.out.println(entry.getKey() + "," + entry.getValue());
        }

    }
}