How to increase array size and copy the elements into the new array?

Question

I have the following classes:

Point

public class Point {

    public Integer x;
    public Integer y;

    public Point(Integer x, Integer y) {
        this.x = x;
        this.y = y;
    }

PointSet

public class PointSet {

    private Point[] arr;
    private int index = 0;

    public PointSet(int capacity) {
        arr = new Point[capacity];
    }

    public PointSet() {
        this(10);
    }

In the PointSet class, I need to implement a method which can add a Point to the internal array and if there is no more room the array size should be doubled and still keeping its original elements.

How can I implement a method which returns a new array with double size and the elements of the internal array?

I am stuck because the default constructor takes 10 as a default value and I can't find a way to double it. I also have to use arrays, so using a list or set won't be an option. Thanks.

The size of an array, once created, is fixed and there is no way to increase it. However as you've mentioned already you can simply replace it after you've copied the values to a new array. Try to iterate over the array(s) using loops. — L.Spillner, Apr 28 '22 at 13:05
You can get the length of an array. So to create a new Array with double the size just do `new Point[arr.length * 2]` — OH GOD SPIDERS, Apr 28 '22 at 13:07
I need to use arrays for this assignment. As I said using List won't be an option. — lopaxxxkzz, Apr 28 '22 at 13:08

score 2 · Answer 1 · answered Apr 28 '22 at 13:21

As others have already said, once an array has been instantiated its size is fixed, so you will have to instantiate a new array, copy the previous content within the new one and ultimately assign the new array to your class' field.

In order to do so, you should define a method in your PointSet class to perform the previous operations.

private void extendCapacity() {
    Point[] temp = new Point[arr.length * 2];
    for (int i = 0; i < arr.length; i++) {
        temp[i] = arr[i];
    }
    arr = temp;
}

So, if you have an add method to insert a new Point, it should look like something like this:

public void add(Point p) {
    if (index == arr.length) {
        extendCapacity();
    }
    arr[index++] = p;
}

Using `Arrays.copyOf` is simpler. – Stephen C Apr 28 '22 at 13:27 — Stephen C, Apr 28 '22 at 13:27
Yes. And `Arrays.copyOf` is simpler. – Stephen C Apr 28 '22 at 13:34 — Stephen C, Apr 28 '22 at 13:34

How to increase array size and copy the elements into the new array?

Point

PointSet

1 Answers1