Java Collection - 如何用相同的键和不同的值替换hashmap中的键和值

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

public class Main {
  public static void main(String args[]) {
    Map<Integer, String> mils = new HashMap<>();
    mils.put(1, "foo");
    mils.put(2, "bar");
    System.out.println("mils:\t" + mils);
    mils.put(1, "bar");
    System.out.println("mils:\t" + mils);
  }
}