Java, filling Object[][] array with data

Question

I'm trying to fill an Object[][] array with data from my Object Class. However im having problems filling the array. Below is what I am trying to do to fill the Object[][] data. at the moment the returned data variable cannot be seen by the method. I have tried removing the method and filling the array where rows in declared but cannot because there is a for loop.

Am I currently filling the object[][] array correctly?

 public class CustomersDialog extends javax.swing.JDialog {
    private CustomerList customers = new CustomerList();
    Object rows[][] = getData();

    public Object[][] getData() {
       customers = dataManager.getUserData();
       int size = customers.size();
       Customer customer = new Customer();

       for(int i = 0; i < size; i++) {
           customer = customers.getCustomerAt(i);
           Object [][] data = { 
           { Integer.toString(customer.getCustomerID()), customer.getfName(), customer.getlName() } };
       }

       return data;
    }
 }

Further doing this method of creating the array outside the loop causes an 'empty statement message' by the compiler and it says it 'requires line ends ; after the .get statements':

 public Object[][] getData() {
    customers = dataManager.getUserData();
    int size = customers.size();
    Customer customer;

    Object [][] data;

    for(int i = 0; i < size; i++) {
        customer = customers.getCustomerAt(i);
        data = { 
        { Integer.toString(customer.getCustomerID()), customer.getfName(), customer.getlName() } };
    }

    return data;
}

Piotr Chojnacki · Accepted Answer · 2013-02-24 11:07:36Z

4

You're not doing it properly.

In your code, you're declaring an array INSIDE for loop, which means that after the loop, the array doesn't exist anymore. That's why you can't return data - it simply does not exist.

More about scope and lifetime of variables you can read there: http://www.c4learn.com/javaprogramming/the-scope-and-lifetime-of-variables-in-java-programming-language/

What you want to do is to declare array outside the loop:

Object [][] data;
for(int i; i < size; i++) {
   // Filling data array
}
return data;

Next thing is that if you want to use an array, you should initialize it first:

Object [][] data = new Object [size][3];

Then you can fill it in for loop, like this:

for(int i; i < size; i++) {
   customer = customers.getCustomerAt(i);
   data[i][0] = Integer.toString(customer.getCustomerID());
   data[i][1] = customer.getfName();
   data[i][2] = customer.getlName();
}

edited Feb 24, 2013 at 11:07

answered Feb 24, 2013 at 10:59

Piotr Chojnacki

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3 Comments

Fabian Barney Over a year ago

An array created inside the for-loop will exist outside as long as the variable is declared outside. So that's not the problem here. But I agree that's not what you want most of the time.

Piotr Chojnacki Over a year ago

Of course I meant declaring a variable inside a for loop, what he had done in his code. Sorry for misunderstanding.

user1851487 Over a year ago

Thank you for the reply, I see the problem I had. All works as expected now.

Aubin · Accepted Answer · 2013-02-24 11:05:39Z

2

You have to allocate the array in two times. Once for the rows, and after once per row.

Object[][] data = new Object[size];
for(int i = 0; i < size; i++) {
   customer = customers.getCustomerAt(i);
   data[i] =
      new Object[]{
         Integer.toString(customer.getCustomerID()),
         customer.getfName(),
         customer.getlName()
      };
   }

edited Feb 24, 2013 at 11:05

answered Feb 24, 2013 at 10:57

Aubin

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Comments

RAN · Accepted Answer · 2013-02-24 11:08:11Z

If you really want to use a 2 dimensional Array than you must define the size of the Array first (also if it is a n dimensional Array!)

See this content to get some clarification:

http://www.leepoint.net/notes-java/data/arrays/arrays-2D.html

It seems to me like you only have one size Parameter for the Array, so I would use a normal Array instead of a 2 dimensional one.

I would do something like this:

public Object[] getData() {
   customers = dataManager.getUserData();
   int size = customers.size();
   Object[] result = new Object[size];
   Customer customer;

   for(int i = 0; i < size; i++) {
       customer = customers.getCustomerAt(i);
       result[i] = { 
       { Integer.toString(customer.getCustomerID()), customer.getfName(), customer.getlName() } };
   }

   return data;
}

If you have to use a 2 dimensional Object Array, than you have to define the second size dimension and fill the array like this:

for(int i = 0; i < sizeDimOne; i++) {
    for(int k = 0; k < sizeDimTwo; k++) {
          result[i][k] = { { Integer.toString(customer.getCustomerID()), customer.getfName(), customer.getlName() } }; 
    }
}

Hope this is helpful.

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