Introduction

• Stack is a legacy class in Java that extends the Vector class.
  • It is known as a legacy class because it was introduced in JDK 1.0 and later modified and integrated into the Java Collections Framework.
  • It is primarily retained for legacy code compatibility and is therefore used very infrequently in modern Java applications.
• It is present in the java.util package.
• It was introduced in JDK 1.0 as part of the original Collection classes.

• Hierarchy:
  • 

• Syntax :-

  package java.util;
  
  public class Stack<E> extends Vector<E>
  {
      // Constructors
      
      // Methods
      
      // Fields
  }

  • Stack extends Vector class and inherits all its methods.

• Stack is a LIFO (Last-In-First-Out) data structure where the last inserted element is the first to be removed.
  
  

Constructors of Stack Class

• Below are the constructors defined in the Stack class:

Methods of Stack Class

• Below are the methods defined specifically in the Stack class:

Program :

• In the below program, we are directly using the Stack class from the java.util package.

• import java.util.Stack;
  
  public class StackDemo
  {
      public static void main(String[] args)
      {
          Stack<String> stack = new Stack<>();
  
          // Pushing elements
          stack.push("Apple");
          stack.push("Banana");
          stack.push("Mango");
          stack.push("Banana"); // duplicate allowed
  
          System.out.println(stack);
  
          System.out.println("-------------------------");
  
          // Accessing top element
          System.out.println("Top Element (peek): " + stack.peek());
  
          System.out.println("-------------------------");
  
          // Popping element
          System.out.println("Popped Element: " + stack.pop());
          System.out.println(stack);
  
          System.out.println("-------------------------");
  
          // Searching element
          System.out.println("Position of 'Apple': " + stack.search("Apple")); // top is position 1
  
          System.out.println("-------------------------");
  
          // Checking if stack is empty
          System.out.println("Is Stack Empty? " + stack.isEmpty());
  
          System.out.println("-------------------------");
  
          // Iterating Stack
          for(String fruit : stack)
          {
              System.out.println(fruit);
          }
      }
  }

  Output:

  [Apple, Banana, Mango, Banana]
  -------------------------
  Top Element (peek): Banana
  -------------------------
  Popped Element: Banana
  [Apple, Banana, Mango]
  -------------------------
  Position of 'Apple': 3
  -------------------------
  Is Stack Empty? false
  -------------------------
  Apple
  Banana
  Mango

Properties of Stack Class:

1. Stack is an index-based data structure, meaning the first element is inserted at index 0.
2. Stack can store heterogeneous elements if generics are not used.
3. Stack allows duplicate elements.
4. Stack allows null values.
5. Stack maintains insertion order, but elements are accessed in LIFO (Last In First Out) manner.
6. Stack does not follow sorting order; sorting must be done explicitly if needed.
7. Stack extends the Vector class, so it is synchronized and thread-safe.
8. Stack guarantees for data consistency.