Question

I am trying to determine if the user entered value already exists in the current array, how to do that?

User entered value to check the variable is
accno and the array to compare to is accnums

This is what i am currently working on

public class Randomtopic {

    static BigDecimal[] accbal = new BigDecimal[20];
    static Integer[] accnums = new Integer[20];

    public static void main(String[] args) {
        displayMenu();
    }

    public static void displayMenu() {
        int option, accno;
        double accbal;
        Scanner sc = new Scanner(System.in);
        System.out.println(" Add an account");
        System.out.println("Search an account with the given account number");
        System.out.print("Enter Your Choice: ");
        option = sc.nextInt();
        switch (option) {
            case 1:
                System.out.println("You have choosen to add account");
                addAccount();
                break;
            case 2:
                System.out.println("You have choosen to search for an account");
                System.out.print("Enter the Account Number: ");
                accno = sc.nextInt();
                System.out.println(search(accno, accnums));
                break;
            default:
                System.out.println("Please choose an appropriate option as displayed");
        }
        displayMenu();
    }

    public static void addAccount() {
        //String accno;
        int i = 0;
        int accno, input;
        BigDecimal accbala;
        DecimalFormat df = new DecimalFormat("0.00");
        //BigDecimal[] accbal= new BigDecimal[20];
        Scanner sc = new Scanner(System.in);
        //String[] accnums = new String[20];
        int j;
        System.out.print("Enter the account number: ");
        accno = sc.nextInt();
        if (String.valueOf(accno).matches("[0-9]{7}")) {
            System.out.print("Enter account balance: ");
            accbala = sc.nextBigDecimal();
            for (j = 0; j < accnums.length; j++) {
                if (accnums[j] == null )
             break;
         else if(accnums[j].equals(accno))
         {
              System.out.println("Account already exists");
         }
            }
            //System.out.print(j);
            if (j == accnums.length) {
                System.out.print("Account storage limit has reached.");

            } else {

                    accnums[j] = accno;
                    accbala = accbala.setScale(2, RoundingMode.HALF_UP);
                    accbal[j] = accbala;

            }
            input = accnums[0];
            System.out.println("The value: " + input + " witha a balance of " + accbal[0].toString());
        } else {
            System.out.println("Wrong NRIC");
        }
        displayMenu();
    }

    public static String search(int accnum, Integer[] numbers) {
        // Integer[] numbers;
        //int key;
        //numbers = accnums;
        // System.out.print("Enter the Account Number: ");        
        for (int index = 0; index < numbers.length; index++) {
            if (numbers[index].equals(accnum)) {
                return String.valueOf(index);
                // System.out.println("The account number exists in this array index :"+index);//We found it!!!
            }
            break;
        }
        return "-1";
    }
}

So my problem?
When i enter the accnum for the first time itself i am getting NullPointerException. Tks

Answer 1

When you instantiate or create an array, the values are by default set to null; whenever you iterate over an array of possibly null values, it is required you skip these. For example,

for(loop conditions)
        if (numbers[index] != null && (numbers[index].equals(accnum))) {
            return String.valueOf(index);
            //your text goes here;
        }
        break;//I suggest you take this line out of your original code. Your for loop will end this once you have iterated through the entire array, or you will automatically break out if you find the value.
}

If you must use an array, then this is the best way to iterate through it. The parenthesis and the && in the if clause prevent you from performing the .equals check if the value of numbers[index] == null – in turn, preventing the null error from being thrown. your only alternative would be to set every value in the numbers[ ] to 0, or some other value, and than skip that value when you iterate. Such would be done with a static final int. However, this is not ideal coding.

Ideally, you should use an ArrayList – you can then not only make this more efficient, but also, much more readable.