Representation of a Stack as an Array

/**
 * Representation of a Stack as an Array in Java
 * Demonstrates push, pop, peek, isEmpty, and isFull operations.
 */
import java.util.Scanner;

class ArrayStack {
    private int[] arr;      // Array to store stack elements
    private int top;        // Index of the top element
    private int capacity;   // Max capacity of the stack

    // Constructor to initialize stack
    public ArrayStack(int size) {
        capacity = size;
        arr = new int[capacity];
        top = -1;  // Indicates an empty stack
    }

    // Push operation: add value to stack
    public void push(int value) {
        if (isFull()) {
            System.out.println("Stack Overflow: Cannot push " + value);
        } else {
            arr[++top] = value;
            System.out.println(value + " pushed into stack");
        }
    }

    // Pop operation: remove and return top element
    public int pop() {
        if (isEmpty()) {
            System.out.println("Stack Underflow: No elements to pop");
            return -1;
        } else {
            return arr[top--];
        }
    }

    // Peek operation: return top without removing
    public int peek() {
        if (isEmpty()) {
            System.out.println("Stack is empty");
            return -1;
        }
        return arr[top];
    }

    // Check if stack is empty
    public boolean isEmpty() {
        return top == -1;
    }

    // Check if stack is full
    public boolean isFull() {
        return top == capacity - 1;
    }

    // Main method to test stack
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter stack capacity: ");
        int size = sc.nextInt();

        ArrayStack stack = new ArrayStack(size);

        stack.push(10);
        stack.push(20);
        stack.push(30);

        System.out.println("Top element is: " + stack.peek());

        System.out.println("Popped: " + stack.pop());
        System.out.println("Popped: " + stack.pop());

        System.out.println("Top element is now: " + stack.peek());

        sc.close();
    }
}