Java – Stack Collection

Stack:

• Stack is an extension of Vector class.
• It follows LIFO – Last In First Out Rule

Methods are:

1. boolean empty() : Tests the stack is empty or not
2. Object peek(): returns the top element of stack but not remove
3. Object pop(): returns the top element of stack and removes
4. void push(Object e): push element on to the stack

import java.util.*; class Code {             public static void main(String[] args) throws Exception {                         Stack<Integer> stk = new Stack<Integer>();                         stk.push(10);                         stk.push(20);                         stk.push(30);                         stk.push(40);                         System.out.println(“Stack is : ” + stk);                           System.out.println(“Pop : ” + stk.pop());                         System.out.println(“Pop : ” + stk.pop());                         System.out.println(“Stack is : ” + stk);                           stk.push(50);                         stk.push(60);                         System.out.println(“Stack is : ” + stk);                           System.out.println(“Peek : ” + stk.peek());                         System.out.println(“Peek : ” + stk.peek());                         System.out.println(“Stack is : ” + stk);             } }

Stack Operations – Menu Driven Program

import java.util.*; class Code {             public static void main(String[] args) throws Exception             {                         Scanner sc = new Scanner(System.in);                         Stack<Integer> stk = new Stack<Integer>();                         while(true)                         {                                     System.out.println(“1.Push \n2.Pop \n3.Display \n4.Peek \n5.Quit”);                                     System.out.print(“Enter choice : “);                                     int ch = sc.nextInt();                                     if(ch==1)                                     {                                                 System.out.print(“Enter element to push : “);                                                 int ele = sc.nextInt();                                                 stk.push(ele);                                                 System.out.println(“Element Pushed”);                                     }                                     else if(ch==2)                                     {                                                 if(stk.empty())                                                             System.out.println(“Empty stack”);                                                 else                                                             System.out.println(“Pop : ” + stk.pop());                                     }                                     else if(ch==3)                                     {                                                 if(stk.empty())                                                             System.out.println(“Empty stack”);                                                 else                                                             System.out.println(“Stack is : ” + stk);                                     }                                     else if(ch==4)                                     {                                                 if(stk.empty())                                                             System.out.println(“Empty stack”);                                                 else                                                             System.out.println(“Peek : ” + stk.peek());                                     }                                     else if(ch==5)                                     {                                                 System.out.println(“End”);                                                 System.exit(1);                                     }                                     else                                                 System.out.println(“Invalid choice”);                         }             } }