Question

Basically, I need to add items to the arraylist. Am I correct in using a separate class (this is in part what I am practicing here) or is that a stupid idea because it is basically just an arraylist. I thought I would create a class because I want to randomise additions to it, etc. Alternately, since it is just an arraylist class, should I use “extends arraylist” or something similar??? Code examples most welcome. I am obviously missing some crucial programming theory here. Thank you.

NOTE I have removed what I think is unrelated code
I have a main:

public class cgame2 extends Activity {

private ArrayList<Integer> cToChooseFromImages; // clear image list

colourlist colourlistused = new colourlist();
colourlist userscolourlist = new colourlist();

....truncated....towards the end of my code I have......
colourlistused.randomaddnewitem();

And I have a class (called colourlist):

import java.util.ArrayList;
import java.util.Random;
import android.util.Log;

public class colourlist {

private ArrayList<Integer> clist;

private int picked;

int imagetodisp;

public colourlist() {
}

public void randomaddnewitem() {
    Random randomtouse = new Random(System.nanoTime());
    picked = randomtouse.nextInt(3);
    clist.add(picked); // this is where the program crashes according to log info
}
public void addnewitem(int itemtoadd) {
    clist.add(itemtoadd);
}

.....etc.....

Answer 1

If you’re adding functionality to ArrayList, the best way is just the way you have done it.

Create a member ArrayList of your class and create functions to extend the behavior. This is called Composition.
Contrast with Inheritance, or creating a subclass of ArrayList, which can create more problems by unnecessarily coupling your implementation to ArrayList.

Don’t forget to initialize the list. The best way would be:

List<Integer> clist = new ArrayList<Integer>();

Use the interface List to make your code more flexible if you choose to change the specific list implementation later.