Java Program for Stack Simulation

Program

import java.io.*;
import java.util.*;
public class stack {
    private final int size = 10;
    private int top;
    private int st[];
    stack() {
        top = -1;
        st = new int[5];
    }
    void push(int item) {
        if (top == size) {
            System.out.println("Stack overflow");
            return;
        } else {
            st[++top] = item;
            System.out.println("Element pushed is:\t" + st[top]);
            return;
        }
    }
    void pop() {
        if (top == -1) {
            System.out.println("Stack underflow");
            return;
        } else {
            System.out.println("Element poped is:\t" + st[top--]);
            return;
        }
    }
    void display() {
        if (top == -1) {
            System.out.println("Stack underflow");
            return;
        } else {
            System.out.println("Contents of stack:");
            for (int i = 0; i <= top; i++)
                System.out.println(st[i]);
            return;
        }
    }
}
public class StackSimulation {
    public static void main(String[] args) {
        stack s = new stack();
        int choice;
        Scanner sc = new Scanner(System.in);
        System.out.println("STACK");
        while (true) {
            System.out.println("1. Push\n2. Pop\n3. Display\n4. Exit");
            System.out.println("Enter choice");
            choice = sc.nextInt();
            switch (choice) {
            case 1:
                System.out.println("Enter the item to push");
                int item = sc.nextInt();
                s.push(item);
                break;
            case 2:
                s.pop();
                break;
            case 3:
                s.display();
                break;
            case 4:
                sc.close();
                System.exit(0);
                break;
            default:
                System.out.println("Invalid choice");
            }
        }
    }
}

Output

STACK
1. Push
2. Pop
3. Display
4. Exit
Enter choice
2
Stack underflow
1. Push
2. Pop
3. Display
4. Exit
Enter choice
1
Enter the item to push
10
Element pushed is:      10
1. Push
2. Pop
3. Display
4. Exit
Enter choice
1
Enter the item to push
20
Element pushed is:      20
1. Push
2. Pop
3. Display
4. Exit
Enter choice
1
Enter the item to push
30
Element pushed is:      30
1. Push
2. Pop
3. Display
4. Exit
Enter choice
3
Contents of stack:
10
20
30
1. Push
2. Pop
3. Display
4. Exit
Enter choice
4