hashmap 遍历的4种方法

 Java HashMap常用方法

hashmap中有4种遍历的方法，以下分别介绍它们的使用

1. Iterator迭代遍历

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

public class HashMapIteratorExample {
    public static void main(String[] args) {
        //通过Map.entrySet使用iterator遍历key和value：
        Map<String, String> map = new HashMap<String, String>();
        map.put("baidu","百度");
        map.put("taobao","淘宝");
        map.put("yxjc123","易学教程");
        map.put("sohu","搜狐");

        Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry<String, String> entry = it.next();
            System.out.println("key= " + entry.getKey() + ", value= " + entry.getValue());
        }

    }
} 

2. map循环遍历

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

public class HashMapEntryExample {
    public static void main(String[] args) {
        //通过Map.entrySet遍历key和value，尤其是容量大时
        Map<String, String> map = new HashMap<String, String>();
        map.put("baidu","百度");
        map.put("taobao","淘宝");
        map.put("yxjc123","易学教程");
        map.put("sohu","搜狐");

        for (Map.Entry<String, String> entry : map.entrySet()) {
            System.out.println("key= " + entry.getKey() + " , value= " + entry.getValue());
        }

    }
} 

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

public class HashMapForExample1 {
    public static void main(String[] args) {
        //通过Map.keySet遍历key和value，普遍使用，二次取值
        Map<String, String> map = new HashMap<String, String>();
        map.put("baidu","百度");
        map.put("taobao","淘宝");
        map.put("yxjc123","易学教程");
        map.put("sohu","搜狐");

        for (String key : map.keySet()) {
            System.out.println("key= "+ key + " , value= " + map.get(key));
        }

    }
} 

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

public class HashMapForExample2{
    public static void main(String[] args) {
        //通过Map.values()遍历所有的value，但不能遍历key
        Map<String, String> map = new HashMap<String, String>();
        map.put("baidu","百度");
        map.put("taobao","淘宝");
        map.put("yxjc123","易学教程");
        map.put("sohu","搜狐");

        for (String v : map.values()) {
            System.out.println("value= " + v);
        }

    }
}