用数组实现堆栈

public class ArrayStackDemo {
    public static void main(String[] args) {
        ArrayStack stack = new ArrayStack(5);
        String key;
        boolean loop = true;
        Scanner scanner = new Scanner(System.in);
        while (loop) {
            System.out.println("===================");
            System.out.println("请输入下列指令");
            System.out.println("show: 展示栈内容");
            System.out.println("pop: 出栈");
            System.out.println("peek: 显示栈顶");
            System.out.println("push: 入栈");
            System.out.println("exit: 退出程序");
            System.out.println("===================");
            key = scanner.next();
            switch (key) {
                case "show":
                    stack.show();
                    break;
                case "push":
                    System.out.println("输入一个数");
                    int value = scanner.nextInt();
                    stack.push(value);
                    break;
                case "peek":
                    try {
                        System.out.println("栈顶数值是:" + stack.peek());
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case "pop":
                    try {
                        int v = stack.pop();
                        System.out.println("出栈数值: " + v);
                    } catch (Exception e) {
                        System.out.println(e.getMessage());
                    }
                    break;
                case "exit":
                    scanner.close();
                    loop = false;
                    break;
                default:
                    break;
            }
        }
        System.out.println("Exit app successfully!");
    }
}


class ArrayStack {
    private int size;
    private int[] arr;
    private int top;

    public ArrayStack(int size) {
        this.size = size;
        arr = new int[size];
        top = -1;
    }

    public boolean isEmpty() {
        return top == -1;
    }

    public boolean isFull() {
        return top == size - 1;
    }

    public void push(int n) {
        if (isFull()) {
            System.out.println("栈已满，无法继续push!");
            return;
        }
        arr[++top] = n;
    }

    public int pop() {
        if (isEmpty()) {
            throw new RuntimeException("栈是空的，pop失败！");
        }
        return arr[top--];
    }

    public int peek() {
        if (isEmpty()) throw new RuntimeException("栈是空的，peek失败！");
        return arr[top];
    }

    public void show() {
        if (isEmpty()) {
            System.out.println("栈是空的，show不出来");
            return;
        }
        for (int i = top; i >= 0; i--) {
            System.out.println(arr[i]);
        }
        System.out.println();
    }
}