public class fff {
    private final int[] stack;
    private int top;//指向新进来的元素的前面

    public fff(int size) {//构造方法
        stack = new int[size];
        this.top = 0;
    }

    public void push(int item) throws Exception {//往栈中添加元素
        if (top > stack.length) {
            throw new Exception("StackOverflowError");
        } else {
            stack[top] = item;
            top++;
        }
    }

    public int pop() throws Exception {//栈顶元素出栈
        if (top == 0) {
            throw new Exception("StackEmpty");
        } else {
            return stack[--top];
        }
    }

    public int peek() throws Exception {//查看栈顶元素
        if (top == 0) {
            throw new Exception("StackEmpty");
        } else {
            return stack[top - 1];
        }
    }
}