Java Programmers

Hello, can anyone fix my assignment my professor said "Before assign iD, must check if the station is available." Can you spot the code that I wrote and understand what he meant by that? I'm assuming he wants my program to be safe where if I already entered an ID at the same position, then it will say "taken choose another one"

Here's my code, I'm making a computerLab it is all done, but I need to make a method to check if the station is available. Makes sense? Help me spot the error

package complab;

import java.util.Scanner;

public class CompLab { public static void main(String[] args) { Scanner scnr = new Scanner(System.in); DisplayMenu(scnr); } public static void DisplayStation(int [][] displaySyntax) { System.out.println("LAB STATUS"); System.out.println("Lab # Computer Stations"); for(int i = 0; i < displaySyntax.length; i++) { System.out.print((i+1)+" "); for(int j = 0; j < displaySyntax[i].length; j++) { if(displaySyntax[i][j] != 0 && displaySyntax[i][j] != -1) { System.out.print((j+1) + ":" + displaySyntax[i][j] + " "); } else { System.out.print((j+1) + ":Empty "); } } System.out.println(); } System.out.println(); } public static void DisplayMenu(Scanner userInput) { int userChoice; int idNumber; int labNumber = -1; int stationNumber = -1; boolean checkUserID; int [][] computerStations = { { 0, 0, 0, 0, 0 }, { 0, 0, 0, 0, 0, 0 }, { 0, 0, 0, 0 }, { 0, 0, 0, 0 } }; DisplayStation(computerStations); while(true) { checkUserID = false; System.out.println(); System.out.println("MAIN MENU"); System.out.println("0) Quit"); System.out.println("1) Simulate Login"); System.out.println("2) Simulate Logoff"); System.out.println("3) Search"); userChoice = userInput.nextInt(); switch(userChoice) { case 0: System.exit(0); case 1: System.out.println("Enter the 5 digit ID number of the user logging in:"); idNumber = userInput.nextInt(); System.out.println("Enter the lab number the user is logging in from (1-4):"); labNumber = userInput.nextInt(); System.out.println("Enter computer station number the user is logging in to (1-6): "); stationNumber = userInput.nextInt(); computerStations[labNumber - 1][stationNumber - 1] = idNumber; DisplayStation(computerStations); break; case 2: System.out.println("Enter the 5 digit ID number of the user to find:"); idNumber = userInput.nextInt(); for(int i = 0; i < computerStations.length; i++) { for(int j = 0; j < computerStations[i].length; j++) { if(computerStations[i][j] == idNumber) { computerStations[i][j] = 0; } } } System.out.println("User " + idNumber + " is logged off"); DisplayStation(computerStations); break; case 3: System.out.println("Enter the 5 digit ID Number of the user to search"); idNumber = userInput.nextInt(); for (int i = 0; i < computerStations.length; i++) { for (int j = 0; j < computerStations[i].length; j++) { if (computerStations[i][j] == idNumber) { labNumber = i + 1; stationNumber = j + 1; checkUserID = true; } } } if(checkUserID == false) { System.out.println("None: The 5 Digit ID you entered does not exist at all"); break; } else { System.out.println("User:" + idNumber + " is logged in lab " + labNumber + " on station " + stationNumber); } break; default: System.out.println("Please enter the number 1 - 3"); } } } }