Question

When I create an array in Java – int array[] and array=new int[some number] –

How can I construct it if I don’t know how many values it will hold so that I have enough space in it?

Answer 1

For growing arrays, use ArrayList.

If the array should contain primitive types, you can wrap them:

ArrayList<Integer> array = new ArrayList<Integer>();

array.add(new Integer(4));
array.add(new Integer(-5));
array.add(new Integer(4));
array.add(new Integer(2));

However, when the values change a lot, you keep instantiating and throwing away Integer instances, because it is immutable. It’s not very high performance either.

My solution: create a wrapper yourself, with a public value field.

This is my wrapper, which is also suitable for TreeMap and the likes, which sort items by their natural order.

public class MyInteger implements Comparable<MyInteger>
{
    public int  value;

    public MyInteger(int value)
    {
        this.value = value;
    }

    @Override
    public String toString()
    {
        return Integer.toString(value);
    }

    @Override
    public int compareTo(MyInteger o)
    {
        return value - o.value;
    }
}

Now you can do stuff like:

array.get(2).value++;