如何删除 hasmap 中的前 2 个密钥对

Question

I asks the user to put 2 key pairs

for (int j = 0; j < 2; j++) {
        System.out.print("Enter student ID " + (j + 1) + ": ");
        id = sc.next();
        System.out.print("Enter student name " + (j + 1) + ": ");
        name = sc.next();
        studentList.put(id, name);
    }

then I removed the last pair the user entered

studentList.remove(id);

I ask for another pair and added it into the hashmap

System.out.println("Enter username: ");
    username = sc.next();
    System.out.println("Enter password: ");
    password = sc.next();
    studentList.put(username, password);

now, I want to ask the user again for another 3 pair

for (int y = 0; y < 3; y++) {
        System.out.print("Enter username " + (y + 1) + ": ");
        username = sc.next();
        System.out.print("Enter password " + (y + 1) + ": ");
        password = sc.next();
        studentList.put(username, password);
    }

but now, I want to remove the first 2 the user put.

Answer 1

You can use interfaces SortedMap or NavigableMap for deleting first two key-pairs, but you can NOT do it with HashMap, because it doesn't save order. As a hashmap has no order it makes no sense to delete the first entry.