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import java.util.Arrays;

public class Test {
    public static void main(String[] args) {
        GenericStack<Integer> numberStack = new GenericStack<>();
        for (int i = 0; i < 10000; i++) {
            numberStack.push(i);
        }
        System.out.println("Current size: " + numberStack.getSize());
        System.out.println("Is stack empty? " + numberStack.isEmpty());
        System.out.println("Pop: " + numberStack.pop());
        System.out.println("Push: " + numberStack.push(1));
        System.out.println("Current Size " + numberStack.getSize());
    }
    static private class GenericStack<E> {
        private int capacity = 100;
        private int size;
        private E[] array = (E[])new Object[capacity];
        public int getSize() {
            return size;
        }
        public void push(E o) {
            array[size++] = o;
            if (size == capacity) {
                E[] tmp = (E[])new Object[capacity *= 2];
                System.arraycopy(array, 0, tmp, 0, array.length);
                array = tmp;
            }
        }
        public E pop() {
            if (size == 0)
                return null;
            else
                return array[--size];
        }
        public boolean isEmpty() {
            return size == 0;
        }
  }
}