current community

your communities

more stack exchange communities

Stack Exchange
tour help
careers 2.0
Take the 2-minute tour ×
Stack Overflow is a question and answer site for professional and enthusiast programmers. It's 100% free, no registration required.
up vote 0 down vote favorite

I think I am making a really basic mistake but after playing around for an hour I cant work this out. I create an array in one method and try and call it in the main method, however I keep getting a null pointer exception when referencing the array from the main method. My class is:

public class test {

    public static String[][] Data;

     public static void createArray() {
            System.out.println("Test 2");

            String[][] Data = new String[2][4];

             Data[0][0] = "13CG43"; //CD ID
             Data[0][1] = "POP"; //Type
             Data[0][2] = "12.99"; //Price
             Data[0][3] = "5"; //Stock

             //Second row
             Data[1][0] = "293DD3"; //CD ID
             Data[1][1] = "HIP"; //Type
             Data[1][2] = "14.99"; //Price
             Data[1][3] = "2"; //Stock

        }


    public static void main(String[] args) {

        try {
            System.out.println("Test1");
            createArray();
            System.out.print("Test3 " + Data[0][0]);

            } catch(Exception e) {
                System.out.println("Error");
            }


    }
}

Thanks,

share|improve this question
1  
In createArray(), you define a local variable 'Data' that override the class static variable 'Data', witch is never initialized. Just use the class variable 'Data', deleting the redefinition "String[][]" in the createArray() method. –  Benoit Courtine Apr 24 '11 at 20:19

2 Answers 2

up vote 4 down vote accepted

That's because the array declaration its inside your function call. Put it only outside and data will be still available after createArray function will be returned.

Change:

String[][] Data = new String[2][4];

with 

Data = new String[2][4];

You were redeclaring Data array inside the createArray function scope. So there were 2 Data array in your program. One global and one local to your function, hiding the global one. The latest, which was the array you were initializing, will be destroyed after the createArray function is returned.

share|improve this answer
up vote 7 down vote 
  public static void createArray() {
            System.out.println("Test 2");

            Data = new String[2][4];

             Data[0][0] = "13CG43"; //CD ID
             Data[0][1] = "POP"; //Type
             Data[0][2] = "12.99"; //Price
             Data[0][3] = "5"; //Stock

             //Second row
             Data[1][0] = "293DD3"; //CD ID
             Data[1][1] = "HIP"; //Type
             Data[1][2] = "14.99"; //Price
             Data[1][3] = "2"; //Stock

        }

You were declaring a new local variable inside the method instead of modifying the global one.

share|improve this answer
    
Brilliant. Thanks! –  Joseph Apr 24 '11 at 20:18
    
+1 but if you add a short explaination you'll make it complete –  MByD Apr 24 '11 at 20:19

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.