Java: Implement a stack using a linked list

Last update on December 21 2024 09:43:02 (UTC/GMT +8 hours)

Write a Java program to implement a stack using a linked list.

Sample Solution:

Java Code:

public class Stack {

  private Node top;
  private int size;

  // Constructor to initialize an empty stack
  public Stack() {
    top = null;
    size = 0;
  }

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

  // Method to push an element onto the stack
  public void push(int data) {
    Node newNode = new Node(data);
    newNode.next = top;
    top = newNode;
    size++;
  }

  // Method to pop an element from the stack
  public int pop() {
    if (isEmpty()) {
      System.out.println("Stack is empty");
      return -1;
    }
    int poppedElement = top.data;
    top = top.next;
    size--;
    return poppedElement;
  }

  // Method to get the top element of the stack
  public int peek() {
    if (isEmpty()) {
      System.out.println("Stack is empty");
      return -1;
    }
    return top.data;
  }

  // Method to display the stack
  public void display() {
    if (isEmpty()) {
      System.out.println("Stack is empty");
    } else {
      Node current = top;
      System.out.print("Stack elements: ");
      while (current != null) {
        System.out.print(current.data + " ");
        current = current.next;
      }
      System.out.println();
    }
  }

  // Inner class representing a node in the linked list
  private class Node {
    int data;
    Node next;

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

  public static void main(String[] args) {
    System.out.println("Initialize a stack using Linked List");
    System.out.println("\nInput some elements on the stack:");
    Stack stack = new Stack();
    stack.push(1);
    stack.push(2);
    stack.push(3);
    stack.push(4);
    stack.push(5);
    stack.display();
    System.out.println("\nTop element: " + stack.peek());
    System.out.println("\nRemove two elements from the stack:");
    stack.pop();
    stack.pop();
    stack.display();
    System.out.println("\nTop element: " + stack.peek());
  }
}

Sample Output:

Initialize a stack using Linked List

Input some elements on the stack:
Stack elements: 5 4 3 2 1

Top element: 5

Remove two elements from the stack:
Stack elements: 3 2 1

Top element: 3

Flowchart:

Live Demo:

Java Code Editor:

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