For loop input in BlueJ (infinite loop)

Question

I'm working on a project for school and am stumped at where I am at the moment. When I run my project, the VM seems to be stuck in a loop and will not load (A console should pop up allowing me to input characters for the CombinationLock class setDigit() method). I believe it has something to do with my for loop in my Interface.java class. If anyone could take a look and lead me in the right direction, that'd be much appreciated. Thanks a bunch!

Interface.java

import java.util.*;
public class Interface
{
    public static void main() {
        Scanner in = new Scanner(System.in);
        CombinationLock combo = new CombinationLock();    

        for(int i = 0; i < 3; i++) {
            String ltr = in.nextLine();
            combo.setDigit(ltr.charAt(0), i);
            System.out.println("Digit " + i + " has been set to " + ltr);
        }
    }
}

CombinationLock.java

public class CombinationLock
{
    String[] combo = new String[3];

    public CombinationLock() { }

    public boolean setDigit(char letter, int index) {
        if (Character.isDigit(letter)) {
            return false;
        }
        combo[index] = String.valueOf(letter);
        return true;
    }

    public boolean unlock(String combo) {
        if (combo.length() > 3) {
            return false; //Longer then it can be, not valid
        }

        char[] comboArray = combo.toCharArray();
        for (char c : comboArray) {
            if (Character.isDigit(c)) {
                return false; //Contains numbers, not valid
            }
        }

        boolean valid = true;
        for (int i = 0; i < 3; i++) {
            if (combo.charAt(i) != comboArray[i] && valid == true) {
                valid = false;
                break;
            }
        }

        return valid;
    }
}

Looks like you should be getting an index-out-of-bounds exception at `combo[index] = String.valueOf(letter);` because `combo` is a zero-length array. — Bhesh Gurung, Oct 29 '12 at 02:01
Try `String[] combo = new String[3];` instead of `String[] combo = {};`. — Bhesh Gurung, Oct 29 '12 at 02:05
I've edited the file to reflect those changes :) @BheshGurung — Josh Ferrara, Oct 29 '12 at 02:08
Check out my answer, it was not able to find your main method, because it has the wrong signature. — Bhesh Gurung, Oct 29 '12 at 02:09
Hint: If you launch from the command line, you (typically) get a very helpful error message in case something goes wrong. — ignis, Oct 29 '12 at 02:12

score 2 · Answer 1 · answered Oct 29 '12 at 02:04

You have initialized combo array in CombinationLock class with length 0 as String[] combo = {};. This is cause ArrayIndexOutOfBoundsException when you are calling combo.setDigit(ltr.charAt(0), i);. Please correct the initialization. I beleive you want to capture 3 inputs, in that case, please initialize combo in CombinationLock with length 3 as below:

     String[] combo = new String[3];

score 1 · Answer 2 · answered Oct 29 '12 at 02:07

1

Your problem is (the signature of the main method is wrong)

 public static void main() {

it should be

 public static void main(String[] args) {

answered Oct 29 '12 at 02:07

Bhesh Gurung

50,430
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This does not seem to be the error, rather I've found the solution myself (I'll be posting what I did wrong). Thanks for your help :) – Josh Ferrara Oct 29 '12 at 02:11

score 0 · Accepted Answer · answered Oct 29 '12 at 02:13

0

I've found where my error was, using the BlueJ IDE one must output something to the console before it shows up and allows you to input data, therefore it never popped up as I never used System.out.println or System.out.print. After doing so, the console popped up and allowed me to input my data. Thanks you for all your suggestions and help!

answered Oct 29 '12 at 02:13

Josh Ferrara

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2
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Wasn't this giving ArrayIndexOutOfBoundsException as I mentioned? – Yogendra Singh Oct 29 '12 at 02:15
Do you know how the IDE lauches the JVM, usually the JVM looks for the main method to invoke from where the application begins. Otherwise the main-class must be different. – Bhesh Gurung Oct 29 '12 at 02:15
When I run the class it allows me to select a method from that class to run. @BheshGurung – Josh Ferrara Oct 29 '12 at 02:29

For loop input in BlueJ (infinite loop)

3 Answers3