Stack Using Linked List

package DataS;

class LinkedListStack {
    private Node top;

    LinkedListStack() {
        this.top = null;
    }
    
    class Node {
        int data;
        Node next;

        Node(int data) {
            this.data = data;
            this.next = null;
        }
    }


    // Push operation: Add an element to the stack
    public void push(int data) {
        Node newNode = new Node(data);
        if (top == null) {
            top = newNode;
        } else {
            newNode.next = top;
            top = newNode;
        }
    }

    // Pop operation: Remove the top element from the stack
    public int pop() {
        if (top == null) {
            System.out.println("Stack is empty");
            return -1;
        }
        int data = top.data;
        top = top.next;
        return data;
    }

    // Peek operation: Get the top element without removing it
    public int peek() {
        if (top == null) {
            System.out.println("Stack is empty");
            return -1;
        }
        return top.data;
    }

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

    // Display the stack elements
    public void display() {
        if (top == null) {
            System.out.println("Stack is empty");
            return;
        }
        Node temp = top;
        while (temp != null) {
            System.out.print(temp.data + " ");
            temp = temp.next;
        }
        System.out.println();
    }

    public static void main(String[] args) {
        LinkedListStack stack = new LinkedListStack();

        // Test push operation
        stack.push(10);
        stack.push(20);
        stack.push(30);
        System.out.println("Stack after pushing 10, 20, 30:");
        stack.display();  // Output: 30 20 10

        // Test pop operation
        System.out.println("Popped element: " + stack.pop());  // Output: 30
        System.out.println("Stack after pop operation:");
        stack.display();  // Output: 20 10

        // Test peek operation
        System.out.println("Top element: " + stack.peek());  // Output: 20

        // Test isEmpty operation
        System.out.println("Is stack empty? " + stack.isEmpty());  // Output: false

        // Pop remaining elements
        stack.pop();
        stack.pop();
        System.out.println("Is stack empty after popping all elements? " + stack.isEmpty());  // Output: true
    }
}