Java address book. How to prevent duplicate contacts in my code?

Question

switch(menuChoice) {

case 1: 
    System.out.println(\"Enter your contact\'s first name:\\n\");
    String fname = scnr.next();
    System.out.println(\"Enter your cont         


        

Answer 1

Use a HashSet. For every user's name, add it to the HashSet.

For example:

HashSet namesUsed = new HashSet();

if (namesUsed.contains(userName)) {
    //do what you want here, if this is entered it means there is a duplicate
} else {
    namesUsed.add(userName); //add it to the list of used names
}