Question

public int Remove(int i, Briefcase c[], String[] m) {

        int nChoice = 0;
        boolean inputisok = false;

        while (inputisok == false) {
            System.out.print("\tPlease remove " + i + " cases: ");
            nChoice = input.nextInt();
            if (c[nChoice] == null || nChoice < 0 && nChoice >= c.length) {
                System.out.println();
                System.out.println("\tInvalid Input please Try again\n");
            } else {
                System.out.println("\tI'm " + m[nChoice]
                        + " You just removed case # " + nChoice);
                System.out.println("\t|" + nChoice + "| contains $"
                        + c[nChoice].getAmount() + "\n");
                inputisok = true;
            }
        }
        return nChoice;
    }

my problem here is that when I enter a letter and a -negative number, or a number that is higher than 27, I always get an exception error, how do I fix that?

Answer 1

The following line is incorrect:

if (c[nChoice] == null || nChoice < 0 && nChoice >= c.length) {

You want to change it like so:

if (nChoice < 0 || nChoice >= c.length || c[nChoice] == null) {

There are two changes: (1) the && became a ||; (2) the clauses have been reordered.

(1) The && is wrong as nChoice < 0 && nChoice >= c.length always evaluates to false, since nChoice can’t be simultaneously less than zero and greater than c.length (Thanks, @Aleks G!)

(2) In your original version you try to access c[nChoice] before making sure nChoice is within the bounds of c. If it isn’t, this’ll result in an ArrayIndexOutOfBoundsException instead of printing out “Invalid Input”.

Short-circuit evaluation is the reason the ordering of clauses matters.

Lastly, before reading from input, you could call hasNextInt() to make sure that the next token can be interpreted as a valid integer.