java map多個值使用相同的key，遍歷map

1.java map多個值使用相同的key

Map<Integer, Integer> map = new IdentityHashMap<>();
map.put(new Integer(1),1);
map.put(new Integer(1), 2);
map.put(new Integer(1), 3);
map.put(new Integer(2), 3);
System.out.println(map.size());

for (Integer row : map.keySet()) {
    System.out.println(row+"===="+map.get(row));
}


2.遍歷map的key和value

public static void main(String[] args) {
    Map<Integer, Integer> map_error = new IdentityHashMap<>();
    //給map_error存放值
    saveMap(map_error);
    Map<Integer, Integer> map = map_error;
    for(Map.Entry<Integer, Integer> entry : map.entrySet()){
        System.out.println("key = " + entry.getKey() + ", value = " + entry.getValue());
    }
}

public static void saveMap(Map<Integer, Integer> map_e){
    map_e.put(new Integer(1),1);
    map_e.put(new Integer(1), 2);
    map_e.put(new Integer(1), 3);
    map_e.put(new Integer(2), 3);

}