Loop test results in null, crashes program

Question

I've been sifting through my code for a project and can't get this method to work as it's designed. What should be happening is that the system searches an array passed as a parameter for a user-inputted value. The following is the entire method as is written (there is some random text I've thrown in for debugging):

    public static void updatePC(int ARRAY_SIZE, int count, String[] customerName, String[] customerID, String[] os, String[] typeOfProblem, int[] turnAroundTime) {
    Scanner keyboard = new Scanner(System.in);
    String toUpdate;
    String[] customerIDClone = new String[count];
    int intToUpdate = -1, loop = count, n;
    char correct = 'n';

    customerIDClone = Arrays.copyOf(customerID, count);
    while (correct == 'n') {
        System.out.println("Please enter the customer ID of the work order you wish to modify");
        toUpdate = keyboard.nextLine();
        if (Arrays.asList(customerIDClone).contains(toUpdate) == true) {
            intToUpdate = Integer.parseInt(toUpdate);
        }
        while (Arrays.asList(customerIDClone).contains(toUpdate) == false) {
            System.out.println("The customer ID you entered was not found. Please try again.");
            toUpdate = keyboard.nextLine();
            intToUpdate = Integer.parseInt(toUpdate);
        }
        System.out.println("Beginning search loop. The value to find is " + toUpdate);
        for (n = 0; n < loop; n++);
        {
            System.out.println("Loop loop looooooooop");
            System.out.println(customerID[n]);
            System.out.println(customerID[0]);
            if (customerID[count].equals(toUpdate)) {
                System.out.println("Found it!");
                count = n;
            }
        }

        System.out.println("Testing run 1.");
    }
    System.out.println("");
    System.out.println("--");
    System.out.println("                    Name:  " + customerName[count]);
    System.out.println("             Customer ID:  " + customerID[count]);
    System.out.println("                      OS:  " + os[count]);
    System.out.println("         Type of Problem:  " + typeOfProblem[count]);
    System.out.println("Expected Turnaround Time:  " + turnAroundTime[count]);
    System.out.println("--");
    System.out.println("Is this new record correct? Please enter y or n.  ");
    correct = keyboard.next().charAt(0);
    keyboard.nextLine();
}

I've been sorting through other questions here on the site and elsewhere, but I can't figure out the issue. The output of the method is

Please enter the customer ID of the work order you wish to modify
3
Beginning search loop. The value to find is 3
Loop loop looooooooop
null
1
Exception in thread "main" java.lang.NullPointerException
    at mckelvey_project3.McKelvey_Project3.updatePC(McKelvey_Project3.java:183)
    at mckelvey_project3.McKelvey_Project3.main(McKelvey_Project3.java:45)
Java Result: 1
BUILD SUCCESSFUL (total time: 7 seconds)

I wrote the line

System.out.println(customerID[0]);

into my code just to demonstrate and make sure that the array is defined and initialized. Additionally,

System.out.println(customerID[1]);

is also defined. It seems the problem exists within my loop test; running

System.out.println(loop + count + n)

reveals that they are all equal to 3. Where is n getting set to 3 at?

EDIT Added the following code suggested by @hfontanez

        customerIDClone = Arrays.copyOf(customerID, count);
    for (int i = 0; i < count; i++) {
        if (customerIDClone[i] == null) {
            System.out.println("Element " + i + " is null. Creating new String.");
            customerIDClone[i] = new String();
        }

and the output is as follows:

Please enter the customer ID of the work order you wish to modify
3
Beginning search loop. The value to find is 3
Loop loop looooooooop
null
2
Exception in thread "main" java.lang.NullPointerException
    at mckelvey_project3.McKelvey_Project3.updatePC(McKelvey_Project3.java:190)
    at mckelvey_project3.McKelvey_Project3.main(McKelvey_Project3.java:45)
Java Result: 1
BUILD SUCCESSFUL (total time: 14 seconds)

EDIT 2 I found the problem... I had a stray ; here:

for (n = 0; n < count; n++);

This issue is now solved.

Answer 1

An array in Java is an object. When you create an array of objects, for instance an array of Strings, you must initialize the array AND each element. The line:

String[] customerIDClone = new String[count];

Initializes an array of 'COUNT' number of String objects, but each element is still null. That is why you are getting a null pointer exception.

Before you invoke customerID[count].equals(toUpdate), the (String) element at customerID[count] must be properly instantiated.

The problem in this case is that the new array is not an exact copy of the original. This line:

customerIDClone = Arrays.copyOf(customerID, count);

Creates a new array of 'COUNT' length. If 'COUNT' is more than the length of the original, all newly created elements are padded with NULL. This explains why customerID[0] works, but not customerID[n]. To fix this, you can iterate through the new array and add a new String() to each NULL element.

UPDATE:

Try this:

customerIDClone = Arrays.copyOf(customerID, count);
for (int i = 0; i < count; i++)
{
    if(customerIDClone[i] == null)
    {
        System.out.println("Element " + i + " is null. Creating new String.");
        customerIDClone[i] = new String();
    }
}