Array not returning correct response with Arrays.binarySearch [duplicate]

Question

Okay so here is my code.

import java.util.*;

//@Author: Tyler Cage
public class main {

public static void main(String[] args) {
    Scanner scnr = new Scanner(System.in);
    String[] userID = new String[3];
    String[] password = new String[3];

    for ( int i = 0; i < userID.length; i++){
        System.out.print("User id at index #" + i + " ");
        userID[i] = scnr.next();
        System.out.print("Password at index #" + i + " ");
        password[i] = scnr.next();
    }

    System.out.print("Enter user id: ");
    String userIdInput = scnr.next();

    System.out.print("Enter password: ");
    String passwordInput = scnr.next();

    int x = Arrays.binarySearch(userID, userIdInput);
    int y = Arrays.binarySearch(password, passwordInput);

    if(x == y){
        System.out.println("Logged in!");
    }
    else{
        System.out.println("Invalid user id/password combo!");
    }        
}

}

I have a weird problem. If I run the program with the array set to 1 then you can log in, but if you run the code as I posted it and try to use the user and pass you set at index 2 it returns a invalid response, as listed below.

    run:
User id at index #0 tyler
Password at index #0 111
User id at index #1 jake
Password at index #1 111
User id at index #2 matt
Password at index #2 111
Enter user id: matt
Enter password: 111
Invalid user id/password combo!
BUILD SUCCESSFUL (total time: 15 seconds)

What am I doing wrong?

Binary search expects the array to be sorted. Unsorted arrays lead to unpredictable results — ernest_k
– ernest_k, Commented Apr 18, 2018 at 15:55
binarySearch will return the first index for the argument. You're searching for 111 which is at index 0, but matt for the username which is at index 2. 2 != 0. — Strikegently
– Strikegently, Commented Apr 18, 2018 at 15:56
@ErnestKiwele 's answer is also correct, but even if the array were sorted, it would still not work. — Strikegently
– Strikegently, Commented Apr 18, 2018 at 15:56

Oleg Cherednik · Accepted Answer · 2018-04-18 15:56:29Z

1

BinarySearch algorithm works only with sorted array:

Arrays.sort(userID);
Arrays.sort(password);
int x = Arrays.binarySearch(userID, userIdInput);
int y = Arrays.binarySearch(password, passwordInput);

answered Apr 18, 2018 at 15:56

Oleg Cherednik

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