Stack Class in Java with Program Example

Stack extends Vector class that implements Last in first out (LIFO) data structure, introduced in JDK 1.0. The data structure specifies the last element to be added to the stack, is the first one to be removed. It is a subclass of the Vector class that enables it to inherit all the attributes and methods of its parent class. It is considered as a legacy class as it exist even before the collection framework and it is re-engineered to support the collection.

Further, it provides only a default constructor to create an empty stack object.

One of the main use case of the Stack class is to reverse a sequence of elements. This can be done by pushing elements onto the stack and then popping them off one by one from the top.

The collection class provides various methods for manipulating elements present in the stack, such as push(), pop(), peek(), and empty().

Methods Of Stack Class

push(): The push method is used to add an element to the top of the stack

pop(): The pop method is used to remove and return the element at the top.

peek(): The peek method returns the element at the top without removing it.

empty(): It returns true if the stack is empty, otherwise, false.

search(): It searches an element, and returns offset, otherwise, -1 to signify not found.

Other Inherited Methods

Here’s a program example to reverse a sequence of integers using Stack:

Program: 

import java.util.Stack;

public class Main
{
  public static void main (String[]args)
  {
    Stack < Integer > stack = new Stack <> ();
    stack.push (1);
    stack.push (2);
    stack.push (3);
    stack.push (4);
    while (!stack.empty ())
      {
  System.out.println ("Element :: "+ stack.pop ());
      }
  }
}

Output:

Element :: 4
Element :: 3
Element :: 2
Element :: 1

Over Stack class, the Deque interface should be used as it provides a more complete and flexible API. The Deque interface extends the Queue interface and supports both LIFO and First-In-First-Out (FIFO) operations. The ArrayDeque class implements the Deque interface which is a resizable array and is a good choice for most use cases.

import java.util.ArrayDeque;
public class Main
{
  public static void main (String[]args)
  {
    ArrayDeque < Integer > deque = new ArrayDeque <> ();
    deque.push (1);
    deque.push (2);
    deque.push (3);
    deque.push (4);
    while (!deque.isEmpty ())
      {
  System.out.println ("Element :: "+deque.pop ());
      }
  }
}

Element :: 4
Element :: 3
Element :: 2
Element :: 1