Java中HashMap遍历的四种方式

骑猪看日落 2022-05-31 05:12 267阅读 0赞

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());
            }
    
        }
    }