Understanding Stack Methods in Java

Table of Contents

1. Introduction
2. Understanding Stack in Java
   • What is Stack?
   • Key Methods of Stack
3. Stack Methods Explained
   • push()
   • pop()
   • peek()
   • search()
4. Example Code and Explanation
5. Conclusion

Introduction

In this article, we will explore one of the core data structures in Java—the Stack. Stacks are widely used in various algorithms, especially for operations like parsing, expression evaluation, and backtracking. In this guide, we’ll focus on some important stack methods, discuss their purpose, and explain them with practical code examples.

Stacks follow a Last In, First Out (LIFO) approach, meaning that the last element added to the stack will be the first one removed. This behavior is fundamental to many problem-solving techniques.

Understanding Stack in Java

What is Stack?

A Stack is a collection that operates in a LIFO manner. Java provides a built-in class, Stack, which extends the Vector class. This means that, in addition to stack-specific operations, you can also use the operations provided by Vector. However, the main focus of stack usage is the four primary methods: push(), pop(), peek(), and search().

Key Methods of Stack

Stack Methods Explained

push()

The push() method is used to add an element to the stack. As soon as an element is pushed, it becomes the topmost item in the stack.

In the example above, 25 is added to the stack. If there were already other elements in the stack, 25 would be placed on top of them.

pop()

The pop() method removes the element at the top of the stack. This method is particularly useful when you need to work in a LIFO order. Once the element is popped, it is removed from the stack.

This line will remove and print the topmost element from the stack.

peek()

The peek() method returns the element at the top of the stack without removing it. It’s used when you only want to inspect the topmost element.

search()

The search() method checks for the presence of a specific element within the stack. If found, it returns the 1-based position of the element relative to the top of the stack. Otherwise, it returns -1.

In this line, the method searches for the element 5 in the stack and returns its position.

Example Code and Explanation

Let’s dive into the actual code that demonstrates the use of stack methods in Java:

Code Breakdown

1. Creating a Stack:
   
   Python

   Stack<Integer> numbers = new Stack<>();

   1	Stack<Integer> numbers = new Stack<>();

   
   This line creates an empty stack that stores integers.
2. Using push() Method:
   
   Python

   numbers.push(25); numbers.push(5);

   1 2	numbers.push(25); numbers.push(5);

   
   These lines add elements to the stack. The first element added will be 25, followed by 5, and so on.
3. Using search() Method:
   
   Python

   System.out.println(numbers.search(5));

   1	System.out.println(numbers.search(5));

   
   This searches for the element 5 in the stack and prints its position.
4. Using pop() Method:
   
   Python

   System.out.println(numbers.pop());

   1	System.out.println(numbers.pop());

   
   This removes the topmost element, which was last added, i.e., 251, and prints it.

Output:

Conclusion

Stacks are a crucial data structure in many problem-solving approaches. The four key methods—push(), pop(), peek(), and search()—make stacks incredibly useful for implementing LIFO behavior. By mastering these methods, you can efficiently work with stack-based algorithms and improve your problem-solving skills in Java.