DynamicArray.java

import java.util.Arrays;

public class DynamicArray{
    private int[] arr;
    private int count = 0;

    private boolean debug = true;

    public DynamicArray(int initialSize){
        arr = new int[initialSize];
    }

    public void add(int element){
        if (count == arr.length)
            expandArray();
        arr[count++] = element;
    }

    private void expandArray(){
        if (debug) System.out.println("Expanding array from " + arr.length + " to " + arr.length *2);
        int[] arr2 = new int[arr.length * 2];
        for (int i = 0; i < arr.length; i++){
            arr2[i] = arr[i];
        }
        arr = arr2;
    }


    /* Insert element at index in arr.
       - If index < 0 or index > count, throw IndexOutOfBoundsException
       - If count == arr.length, expand array
       - If index < count shift elements right from count to index
     */
    public void insert(int index, int element){
        if (index < 0 || index > count) throw new IndexOutOfBoundsException();
        if (count == arr.length) expandArray();
        for (int j = count; j > index; j--){
            arr[j] = arr[j-1];
        }
        arr[index] = element;
        count++;
    }

    public int get(int index){
        if (index < 0 || index >= count) throw new IndexOutOfBoundsException();
        return arr[index];
    }

    public String toString(){
        return String.join(", ", Arrays.stream(arr)
                                       .limit(count)
                                       .mapToObj(String::valueOf)
                                       .toArray(String[]::new));
    }

    // Testing
    public static void main(String[] args){
        DynamicArray da = new DynamicArray(2);
        da.add(5);
        da.add(12);
        da.add(7);
        da.insert(1, 3);
        da.insert(0, 4);
        da.insert(5, 10);
        System.out.println("get idx 3 " + da.get(3));
        System.out.println(da);
    }
}