How to check if a client already exist in array in java [duplicate]

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
– Arnaud, Commented Nov 9, 2018 at 10:43

Davide Lorenzo MARINO · Accepted Answer · 2018-11-09 10:48:44Z

2

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.

answered Nov 9, 2018 at 10:48

Davide Lorenzo MARINO

27k4 gold badges45 silver badges58 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Arnault Le Prévost-Corvellec · Accepted Answer · 2018-11-09 10:51:33Z

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 9, 2018 at 10:51

Arnault Le Prévost-Corvellec

5252 silver badges9 bronze badges

answered Nov 9, 2018 at 10:46

Tim Biegeleisen

526k32 gold badges323 silver badges399 bronze badges

3 Comments

vikingsteve Over a year ago

Why not a Set if ordering is unimportant?

Tim Biegeleisen Over a year ago

@vikingsteve I changed to set, but I thought the OP might want to preserve the order in which the usernames had been entered.

Tu.Ma. Over a year ago

To preserve insertion order, a LinkedHashSet can be used. docs.oracle.com/javase/6/docs/api/java/util/LinkedHashSet.html

Collectives™ on Stack Overflow

How to check if a client already exist in array in java [duplicate]

2 Answers 2

Comments

3 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

3 Comments

Linked

Related