map的三种遍历

public class MapTest {

    public static void main(String args[]){
        
        Map<String, Integer> map = new HashMap<>();
        List list =new ArrayList<>();
        System.out.println(list.size());
        
        map.put("1", 1);
        map.put("2", 2);
        map.put("3", 3);
        map.put("4", 4);
//采用keyset()迭代器
        Iterator iterator =map.keySet().iterator();
        while (iterator.hasNext()) {
            Object key=  iterator.next();
            System.out.println("key: "+key + "值为："+map.get(key));
        }
        
        Object key;
        Object value;
//采用entryset()迭代
        Iterator  iterator2=map.entrySet().iterator();
        while (iterator2.hasNext()) {
            Map.Entry entry = (Map.Entry) iterator2.next();
            key = entry.getKey();
            value=entry.getValue();
            System.out.println("key:"+key +"value:"+value);
        }
        
        System.out.println();
//采用foreach
        for (String key1 : map.keySet()) {
            System.out.println("key1:"+key1 + "value ："+map.get(key1));
        }
    }
        
}