How to check if a client already exist in array in java

Question

Newbie here.

I just want to ask, how to disallow someone to enter the same element in an array?

this is my code currently and it's not working properly:

import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner input=new Scanner(System.in);
        String[] username=new String[5];    
        for (int c=0;c<5;c++)
    {
        System.out.print("Enter client name: ");
        username[c]=input.nextLine();
        if (username.equals(username[c]))
        {
            System.out.println("The client already exist.");
        }
    }
    }
}

p.s. I hope you guys can help me.

`username.equals(username[c])` is comparing a `String[]` with a `String` . — Arnaud, Nov 09 '18 at 10:43

score 2 · Answer 1 · edited Nov 09 '18 at 10:51

2

Try using a data structure such as a set, which makes it easy to determine if a certain username be already present:

public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    Set<String> users = new HashSet<>();

    while (users.size() < 5) {
        System.out.print("Enter client name: ");
        String username = input.nextLine();

        if (!users.add(username)) {
            System.out.println("The client already exist.");
        }
    }
}

edited Nov 09 '18 at 10:51

Arnault Le Prévost-Corvellec

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answered Nov 09 '18 at 10:46

Tim Biegeleisen

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1

Why not a `Set` if ordering is unimportant? – vikingsteve Nov 09 '18 at 10:46
@vikingsteve I changed to set, but I thought the OP might want to preserve the order in which the usernames had been entered. – Tim Biegeleisen Nov 09 '18 at 10:47
To preserve insertion order, a LinkedHashSet can be used. https://docs.oracle.com/javase/6/docs/api/java/util/LinkedHashSet.html – Tu.Ma. Nov 09 '18 at 10:51

score 2 · Answer 2 · answered Nov 09 '18 at 10:48

While you can use an array to handle this problem in java there is a data structure that handle your problem very easily.

This data structure is a Set:

A collection that contains no duplicate elements. More formally, sets contain no pair of elements e1 and e2 such that e1.equals(e2), and at most one null element. As implied by its name, this interface models the mathematical set abstraction.

How to check if a client already exist in array in java

2 Answers2