package queue; public class Stack { private int[] items = new int[100]; private int top = -1; //index to keep track of the topmost element public boolean isEmpty() { return top < 0; } public void push(int item) { if (top == items.length-1) throw new RuntimeException("Stack is full"); items[++top] = item; } /** * Returns the topmost item and removes it * @return */ public int pop() { if (isEmpty()) throw new RuntimeException("Stack is empty"); return items[top--]; } /** * Returns the topmost item without removing it * Peek and Pop methods should ideally be invoked after checking that the stack is not empty * either in a 'if' condition or a 'while' loop * @return */ public int peek() { if (isEmpty()) throw new RuntimeException("Stack is empty"); return items[top]; } public static void main(String[] args) { Stack stack = new Stack(); System.out.println(stack.isEmpty()); stack.push(5); stack.push(4); stack.push(6); stack.push(10); System.out.println(stack.isEmpty()); System.out.println(stack.peek()); System.out.println(stack.pop()); System.out.println(stack.peek()); System.out.println(stack.pop()); System.out.println(stack.pop()); System.out.println(stack.pop()); } }