package Stack;

/**

 * Created by Frank

 */

public class MyStack<T> implements SimpleStack<T> {

    public static void main(String[] args) {

        MyStack<String> stack = new MyStack<>();

        stack.push("Frank");

        stack.push("Smith");

        System.out.println(stack.pop());

    }

    private int depth = 0;

    public static final int DEFAULT_INITIAL = 10;

    private T[] stack;

    public MyStack() {

        this(DEFAULT_INITIAL);

    }

    public MyStack(int howBig) {

        if (howBig <= 0) {

            throw new IllegalArgumentException(howBig + " must be positive, but was " + howBig);

        }

        stack = (T[]) new Object[howBig];

    }

    @Override

    public boolean empty() {

        return depth == 0;

    }

    @Override

    public void push(T obj) {

        stack[depth++] = obj;

    }

    @Override

    public T pop() {

        --depth;

        T tmp = stack[depth];

        stack[depth] = null;

        return tmp;

    }

    @Override

    public T peek() {

        if (depth == 0) {

            return null;

        }

        return stack[depth - 1];

    }

}