Question

Basically, I want to create a 2-D array that grows in size at runtime. Could I do this using a vector in Java?

Would these be right then?

int [] [] x = new x [100] [100];

Vector x= new Vector();

To add elements into the array-

for i=0 to 99
   for j=0 to 99
   x.addElement(x[i] [j]);

essentially, it would be just the same like referencing any other object, only here, I’ve to specify the index numbers as well, right?

I’m a novice at Java. So I’d appreciate any help!

Answer 1

Unfortunately, Java has neither 2D arrays nor 2D growing vectors.

It has array of arrays or vector of vectors.

In your example, you created 1D vector of Objects:

Vector x= new Vector();

is similar to growing array of type Object[] x

So, when you do

y.addElement(x[i][j]);

Java does “boxing”, i.e. it does

y.addElement(new Integer(x[i][j]));

Since you added 100×100 elements into 1D array, you will need to calculate location yourself

y.get(i*numcols+j)

So, to avoid all this, use vector of vectors like example below. The example copies newly fixed size array into vector of vectors:

   // creates fixed size 2D array with zeros
    int [] [] x = new int [50][50]; 

    // creates empty vector of vectors of integers
    // y is of type Vector<Vector<Integer>>
    // y.get(row) is of type Vector<Integer>>
    // y.get(row).get(col) is of type Integer
    Vector<Vector<Integer>> y = new Vector<Vector<Integer>>(); 

    // set the size of vector of vectors (number of rows)
    // each row will be null for now
    y.setSize(x.length);

    // enumerating rows
    for(int row=0; row<x.length; ++row) {

        log.info("row {}", row);

        // assign empty vector for row
        y.set(row, new Vector<Integer>());

        // set row size (number of columns)
        y.get(row).setSize(x[row].length);

        // enumerating columns of current row
        for(int col=0; col<x[row].length; ++col) {

            // setting the value for a cell
            y.get(row).set(col, x[row][col]);

        }
    }