Java經典實例：進階版堆棧完成，支持任何對象類型

支持任何對象類型，有更多的錯誤反省。

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];
    }
}