public class CustomArrayList {

    private Object[] arr;
    private int count;
    private static final int INITIAL_CAPACITY = 4;


    public static void main(String[] args){
        CustomArrayList shoppingList = new CustomArrayList();
      /**  shoppingList.add("Milk");
        shoppingList.add("Honey");
        shoppingList.add("Olives");
        shoppingList.add("Beer");
        shoppingList.remove("Olives");
      */
        System.out.println("We need to buy:");

        for(int i=0; i<shoppingList.getLength(); i++) {
            System.out.println(shoppingList.elementAt(i));
        }

        System.out.println("Do we have to buy Bread? " +
                shoppingList.contains("Bread"));
    }

    /** Initializes the array-based list – allocate memory **/

    public CustomArrayList() {
        arr = new Object[INITIAL_CAPACITY];
        count = 0;
    }

    /**
     * @return the actual list length
     */

    public int getLength() {
        return count;
    }

    /**
     * Adds element to the list
     * @param item - the element you want to add
     */

    public void add(Object item) {
        add(count, item);
    }

    /**
     * Inserts the specified element at given position in this list
     * @param index -
     *        index at which the specified element is to be inserted
     * @param item -
     *        element to be inserted
     * @throws IndexOutOfBoundsException
     */

    public void add(int index, Object item) {
        if (index>count || index<0) {
            throw new IndexOutOfBoundsException(
                    "Invalid index: " + index);
        }

        Object[] extendedArr = arr;
        if (count + 1 == arr.length) {
            extendedArr = new Object[arr.length * 2];
        }

        System.arraycopy(arr, 0, extendedArr, 0, index);
        count++;
        System.arraycopy(
                arr, index, extendedArr, index+1, count-index-1);
        extendedArr[index] = item;
        arr = extendedArr;
    }

    /**
     * Returns the index of the first occurrence of the specified
     * element in this list.
     *
     * @param item - the element you are searching
     * @return the index of given element or -1 is not found
     */

    public int indexOf(Object item) {
        if (item == null) {
            for (int i = 0; i < arr.length; i++) {
                if (arr[i] == null)
                    return i;
            }
        } else {
            for (int i = 0; i < arr.length; i++)
                if (item.equals(arr[i]))
                    return i;
        }
        return -1;
    }

    /**
     * Clears the list
     */

    public void clear() {
        arr = new Object[0];
        count = 0;
    }

    /**
     * Checks if an element exists
     * @param item – the item to be checked
     * @return if the item exists
     */

    public boolean contains(Object item) {
        int index = indexOf(item);
        boolean found = (index != -1);
        return found;
    }

    /**
     * @return the object on given position
     */

    public Object elementAt(int index) {
        if (index>=count || index<0) {
            throw new IndexOutOfBoundsException(
                    "Invalid index: " + index);
        }

        return arr[index];
    }

    /**
     * Removes the element at the specified index
     * @param index - the index, whose element you want to remove
     * @return the removed element
     */

    public Object remove(int index) {
        if (index>=count || index<0) {
            throw new IndexOutOfBoundsException(
                    "Invalid index: " + index);
        }

        Object item = arr[index];
        System.arraycopy(arr, index+1, arr, index, count-index+1);
        arr[count - 1] = null;
        count--;
        return item;
    }

    /**
     * Removes the specified item and returns its index or -1
     * if item does not exists
     * @param item - the item you want to remove
     */

    public int remove(Object item) {
        int index = indexOf(item);
        if (index == -1) {
            return index;
        }

        System.arraycopy(arr, index+1, arr, index, count-index+1);
        count--;
        return index;
    }
}