Introduction to Stack in Java

// Java program to implement stack operations using array
class Stack {

    static final int MAX = 100;  // Maximum size of stack
    int top;
    int[] arr = new int[MAX];

    // Constructor
    Stack() {
        top = -1;
    }

    // Check if stack is empty
    boolean isEmpty() {
        return (top < 0);
    }

    // Push operation
    boolean push(int x) {
        if (top >= MAX - 1) {
            System.out.println("Stack Overflow");
            return false;
        } else {
            arr[++top] = x;
            System.out.println(x + " pushed into stack");
            return true;
        }
    }

    // Pop operation
    int pop() {
        if (top < 0) {
            System.out.println("Stack Underflow");
            return -1;
        } else {
            return arr[top--];
        }
    }

    // Peek operation
    int peek() {
        if (top < 0) {
            System.out.println("Stack is Empty");
            return -1;
        } else {
            return arr[top];
        }
    }
}

public class Main {
    public static void main(String[] args) {

        Stack stk = new Stack();

        stk.push(20);
        stk.push(40);
        stk.push(60);

        System.out.println("Element popped: " + stk.pop());
        System.out.println("Top element is: " + stk.peek());
    }
}