Question: You need to store unique user IDs for a web application.
Which collection would be most suitable for this purpose, and why?
Answer: I would use a HashSet for storing unique user IDs because it does not allow duplicate entries and offers average O(1) time complexity for add, remove, and contains operations. Here’s an example:
Addition (add()): O(1) average case, O(n) worst case.
Removal (remove()): O(1) average case, O(n) worst case.
Search (contains()): O(1) average case, O(n) worst case.
package com.example.demo;
import java.util.HashSet;
public class UserManager {
private HashSet<String> userIDs;
public UserManager() {
userIDs = new HashSet<>();
}
public boolean addUserID(String userID) {
return userIDs.add(userID); // returns false if the userID already exists
}
public boolean removeUserID(String userID) {
return userIDs.remove(userID);
}
public boolean containsUserID(String userID) {
return userIDs.contains(userID);
}
public static void main(String[] args) {
UserManager manager = new UserManager();
manager.addUserID("user123");
System.out.println(manager.containsUserID("user123")); // Output: true
manager.removeUserID("user123");
System.out.println(manager.containsUserID("user123")); // Output: false
}
}
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