public class ArrayStack implements Stack {
	private Object[] a;
	private int size;

	public ArrayStack(int capacity) {
		a=new Object[capacity];
	}

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

	public Object peek(){
		if (size==0) throw new IllegalStateException("stack is empty");
		return a[size-1];
	}
	public Object pop(){
		if (size==0) throw new IllegalStateException("stack is empty");
		Object object=a[--size];
		a[size]=null;
		return object;
	}

	public void push(Object object){
		if (size==a.length) resize();
		a[size++]=object;
	}
	
	public int size(){
		return size;
	}

	private void resize(){
		Object[] aa=a;
		a=new Object[2*aa.length];
		System.arraycopy(aa,0,a,0,size);
	}
	public void reverse(){
		Object[] aa=a;
		a=new Object[aa.length];
		System.arraycopy(aa,1,a,0,--size);
		
	}
}