HashMap 을 옮 겨 다 니 는 몇 가지 방법:keyset 과 entry Set

public class Demo05MayKeySet {
    public static void main(String[] args) {
        showKeySet();
    }

    private static void showKeySet() {
        Map<String, Integer> redVelvet = new HashMap<>();
        redVelvet.put("Irene", 29);
        redVelvet.put("Seulgi", 26);
        redVelvet.put("Wendy", 26);
        redVelvet.put("Joy", 24);
        redVelvet.put("yeri", 21);

        //1.  Map      keySet(), Map     key   ,     Set   
        Set<String> rv = redVelvet.keySet();

        //2.  set  ,  Map       key
        Iterator<String> it = rv.iterator();
        while (it.hasNext()) {
            String name = it.next();
            //3.  Map      get(key),  key  value
            Integer age = redVelvet.get(name);
            System.out.println(name+": "+age);
        }
        System.out.println("--------------------");

        //      for  
        for(String name : rv){
            Integer age = redVelvet.get(name);
            System.out.println(name+": "+age);
        }

        System.out.println("--------------------");

        //     
        for(String name : redVelvet.keySet()){
            Integer age = redVelvet.get(name);
            System.out.println(name+": "+age);
        }
    }
}

Seulgi: 26
Joy: 24
Irene: 29
yeri: 21
Wendy: 26
--------------------
Seulgi: 26
Joy: 24
Irene: 29
yeri: 21
Wendy: 26
--------------------
Seulgi: 26
Joy: 24
Irene: 29
yeri: 21
Wendy: 26