Data Structure: Stack

Stack.java

//Stack
//Author: Milon

import java.util.NoSuchElementException;

//Node class
class Node{
    //Instance variable
    protected Object data;
    private Node nextNode;

    //Constructor
    public Node(){
        data = null;
        nextNode = null;
        }

    public Node(Object item, Node next){
        data = item;
        nextNode = next;
        }

    //Set methods
    public void setData(int item){
        data = item;
        }

    public void setNextNode(Node next){
        nextNode = next;
        }

    //Get methods
    public Object getData(){
        return data;
        }

    public Node getNextNode(){
        return nextNode;
        }

    //Overloaded toString method
    public String toString(){
        return "" + data;
        }
    }

//Stack class
public class Stack{
    //Instance variable
    private Node top;
    private int size;

    //Constructor
    public Stack(){
        top = null;
        size = 0;
        }

    //Returns is the stack empty
    public boolean isEmpty(){
        return top == null;
        }

    //Returns size of the stack
    public int size(){
        return size;
        }

    //Push method
    public void push(Object item){
        top = new Node(item, top);
        ++size;
        }

    //Pop method
    public Object pop(){
        if(!isEmpty()){
            Node current = top;
            top = top.getNextNode();
            --size;
            return current.getData();
            }
        else{
            System.out.println("Stack underflow.");
            //throw new NoSuchElementException();
            return null;
            }
        }

    //Peek method
    public Object peek(){
        if(!isEmpty())
            return top.getData();
        else{
            System.out.println("Stack underflow.");
            //throw new NoSuchElementException();
            return null;
            }
        }

    //Overloaded toString method to show the entire list
    public String toString(){
        String str = "[ ";
        if(top != null){
            str += top.getData();
            Node current = top.getNextNode();
            while(current.getNextNode() != null){
                str += ", " + current.getData();
                current = current.getNextNode();
                }
            str += ", " + current.getData();
            }
        str += " ]";
        return str;
        }

    }

StackImplement.java

//Stack Implementation class
//Author: Milon

import java.util.Scanner;
import java.util.Random;

public class StackImplement{
    public static void main(String args[]){
        Scanner input = new Scanner(System.in);
        Random rand = new Random();
        Stack stack = new Stack();

        System.out.print("How many number of element do you want: ");
        int n = input.nextInt();

        for(int i=0;i<n;i++)
            stack.push(new Integer(rand.nextInt(100)));

        while(true){
            System.out.println("\n\n");
            System.out.println("* * * * * Stack Implementation * * * * *");
            System.out.println("1\. Show the whole stack.");
            System.out.println("2\. Show does the stack empty.");
            System.out.println("3\. Show the top element.");
            System.out.println("4\. Insert an element.");
            System.out.println("5\. Delete an element.");
            System.out.println("6\. Show the stack size.");
            System.out.println("7\. Exit.");
            System.out.println("\n\n");

            System.out.print("Enter your choice: ");
            int choice = input.nextInt();

            switch(choice){
                case 1:
                        System.out.println("The stack is: "+stack.toString());
                        break;

                case 2:
                        if(stack.isEmpty())
                            System.out.println("The stack is empty.");
                        else
                            System.out.println("The stack is not empty.");
                        break;

                case 3:
                        System.out.println("The top element is "+stack.peek());
                        break;

                case 4:
                        System.out.print("Inter the element: ");
                        int item = input.nextInt();
                        stack.push(new Integer(item));
                        System.out.println("Item inserted successfully.");
                        break;

                case 5:
                        System.out.println("Item "+stack.pop()+" deleted successfully.");
                        break;

                case 6:
                        if(stack.isEmpty())
                            System.out.println("The stack is empty.");
                        else
                            System.out.println("Size of the stack is "+stack.size());
                        break;

                case 7:
                        System.exit(1);
                        break;

                default:
                        break;
                }
            }

        }
    }