Question

Can the size of dynamic array be changed

Answer 1

No, you can't change the size of an array once created. You either have to allocate it bigger than you think you'll need or accept the overhead of having to reallocate it needs to grow in size. When it does you'll have to allocate a new one and copy the data from the old to the new:

int oldItems[] = new int[10];
for (int i=0; i<10; i++) {
  oldItems[i] = i+10;
}
int newItems[] = new int[20];
System.arraycopy(oldItems, 0, newItems, 0, 10);
oldItems = newItems;

Answer 2

import java.util.List;
import java.util.ArrayList;
import java.util.Random;

public class A  {

    public static void main( String [] args ) {
        // dynamically hold the instances
        List<xClass> list = new ArrayList<xClass>();

        // fill it with a random number between 0 and 100
        int elements = new Random().nextInt(100);  
        for( int i = 0 ; i < elements ; i++ ) {
            list.add( new xClass() );
        }

        // convert it to array
        xClass [] array = list.toArray( new xClass[ list.size() ] );


        System.out.println( "size of array = " + array.length );
    }
}
class xClass {}