Adding int to an array

Question

First off don't call this a duplicate unless you actually find a thread that works for exactly what I'm trying to do, as I've gone through about 50 threads that aren't helping.

~Problem: I don't know how to correctly add an integer to an array like "private int test[] ={}"

~My code:

private int generatedList[] = {};
private int lastInt = 1;

    private void startList() {
        if (generatedList.length == 30000) {
            System.out.println(generatedList);
        } else {
            generatedList[lastInt+1] = generatedList[lastInt];
            lastInt++;
            System.out.println(generatedList);
            startList();
        }
    }

~What I'm trying to accomplish: if the length of the list is less than 30,000 add the last int to the array then lastInt++, so after looping say 5 times the list will print like this: 1,2,3,4,5

How do I add the "lastInt" to the generatedList[]?

You can't put anything into an array of length 0. Also, arrays do NOT have dynamic length. — G. Bach
– G. Bach, Commented Jan 10, 2014 at 18:27
Arrays are not extendible by design. If you want to add to an array, you need to create a new array and copy over the contents. I suggest using ArrayList, because it's array-like, and you can add/remove to it. — ashes999
– ashes999, Commented Jan 10, 2014 at 18:27
Also, (and this is general for many languages) you can't grow an array once it has been created. Look at ArrayList and friends. — user
– user, Commented Jan 10, 2014 at 18:27
@Ryan I would also like to point out an unrelated issue: your recursive implementation is going to be way, way less efficient than simply looping using a counter from 1..30000. — zjm555
– zjm555, Commented Jan 10, 2014 at 18:36

Alexis C. · Accepted Answer · 2014-01-10 20:50:41Z

8

Arrays in Java are of a fixed size. The one you declared is of size 0, in fact. You won't be able to append to the end of it. Check out the ArrayList class, it will help you.

private ArrayList<Integer> generatedList;
...
generatedList.add(1234);

However, there is a bigger problem with your code. Your recursive implementation is going to be extremely slow, and it doesn't have an initialization for the first value in the array. It would be much better to use a primitive array of fixed size 30,000, and simply loop from 0..30k and fill in the values by index. I leave that as an exercise for you since this is probably related to some homework assignment :)

edited Jan 10, 2014 at 20:50

Alexis C.

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answered Jan 10, 2014 at 18:27

zjm555

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Alexis C. · Accepted Answer · 2014-01-10 20:50:54Z

4

Arrays are not extendible. This is by design.

I suggest using an ArrayList. It's like an array (can index any property, works almost as fast in terms of runtime complexity) but has the additional properties that you can add and remove items.

The easy way to do this is to change generatedList into ArrayList<Integer>. If you want to preserve an array, you can always create a new array and copy over the contents. (ArrayLists are easier, though.)

edited Jan 10, 2014 at 20:50

Alexis C.

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answered Jan 10, 2014 at 18:28

ashes999

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Μenelaοs · Accepted Answer · 2014-01-10 18:29:20Z

3

Your trying to add new elements to an array of size zero size. Use an arraylist or specify array size first.

answered Jan 10, 2014 at 18:29

Μenelaοs

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