import java.util.Arrays;

public class ArrayList {

    private static Object[] array = new Object[16];
    private int size = 0;

    public void add(Object e) {
        if (size - array.length >= 0) {
            ensureCapacity(size + 1);
        }

        array[size++] = e;

    }

    public void add(int i, Object e) {

        if ((i >= size) || (i < 0)) {
            throw new IndexOutOfBoundsException();
        }
        if (size - array.length > 0) {
            ensureCapacity(size + 1);
        }

        for (int j = size-1; j >= i; j--) {

            array[j+1] = array[j];
        }
        array[i] = e;
        size++;
    }

    public void clear() {
        for (int i = 0; i < size; i++) {
            array[i] = null;
        }
        size = 0;
    }

    public boolean contains(Object e) {
        if (e == null) {
            for (int i = 0; i < size; i++) {
                if (array[i] == null) {
                    return true;
                }
            }
        } else {
            for (int i = 0; i < size; i++) {
                if (e.equals(array[i])) {
                    return true;
                }
            }
        }
        return false;
    }

    public void ensureCapacity(int minCapacity) {
        if (minCapacity > array.length) {
            Arrays.copyOf(array, (minCapacity - 1) * 2);
        }

    }

    public Object get(int i) {
        if ((i >= size) || (i < 0)) {
            throw new IndexOutOfBoundsException();
        }
        return array[i];
    }

    public int indexOf(Object e) {

        if (e == null) {
            for (int i = 0; i < size; i++) {
                if (array[i] == null) {
                    return i;
                }
            }
        } else {
            for (int i = 0; i < size; i++) {
                if (e.equals(array[i])) {
                    return i;
                }
            }
        }
        return -1;
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public Object remove(int i) {
        if ((i >= size) || (i < 0)) {
            throw new IndexOutOfBoundsException();
        }
        Object a = array[i];
        for (int j = i + 1; j < size; j++) {
            array[j - 1] = array[j];
        }
        array[size - 1] = null;
        size--;

        return a;
    }

    public boolean removeObject(Object e) {
        int i = indexOf(e);
        if (i != -1) {
            remove(i);
            // а извлеченный элемент остается в памяти?
            return true;
        }
        return false;

    }

    public Object set(int i, Object e) {
        if ((i >= size) || (i < 0)) {
            throw new IndexOutOfBoundsException();
        }
        Object a = array[i];
        array[i] = e;
        return a;
    }

    public int size() {
        return size;
    }

    public Object[] trimToSize() {

        Object[] newarray = new Object[size];
        int i = 0;
        while (array[i] != null) {
            newarray[i] = array[i];
            i++;
        }
        return newarray;

    }

}