map的遍历方式

package b;

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

public class MapTest {
    /**
     * 可以有重复的value,但是key不可重复
     * @param args
     */
    public static void main(String[] args) {
        Map<Integer, String> map = new HashMap<Integer, String>();
        map.put(1, "中国");
        map.put(2, "美国");
        map.put(3, "俄罗斯");
        map.put(4, "中国");
        map.put(4, "中国");
        map.put(null, "土耳其");
        map.put(null, "啊啊");
        System.out.println(map.size());

        /**
         * 1、通过Map.keySet遍历key和value
         */
        /*Set<Integer> keySet = map.keySet();
        for (Integer key : keySet) {
            String value = map.get(key);
            System.out.println("key:" + key + "  value:" + value);
        }*/
        
        /**
         * 2、通过Map.entrySet使用iterator遍历
         */
        /*Set<Entry<Integer, String>> entrySet = map.entrySet();
        Iterator<Entry<Integer, String>> it = entrySet.iterator();
        while(it.hasNext()){
            Entry<Integer, String> entry = it.next();
            Integer key = entry.getKey();
            String value = entry.getValue();
            System.out.println("key:" + key + "  value:" + value);
        }*/
        /**
         * 3、通过Map.entrySet使用foreach
         */
        Set<Entry<Integer, String>> entrySet = map.entrySet();
        for (Entry<Integer, String> entry : entrySet) {
            Integer key = entry.getKey();
            String value = entry.getValue();
            System.out.println("key:" + key + "  value:" + value);
        }
        
    }
    

}