Java Program to Reverse a String Using Stack

Last Updated : 17 Mar 2025

The stack is a linear data structure that is utilized to store the collection of objects. It depends on Last in First Out (LIFO). Java Collections structure gives numerous points of interaction and classes to store objects. One of them is the Stack class which gives various activities like push, pop, search, and so forth.

Approach to reverse a string using stack

Push the elements/characters of the string individually into the stack of datatype characters.
Pop the elements/characters individually from the Stack until the stack becomes vacant.
Add a popped component to the character array.
Convert character array to string.
Return turned around the string.

The implementation of the above approach is as shown below

// Java Program to Reverse a String using Stack
// importing the required packages
import java.io.*;
import java.util.*;
class StringReverse {
    // This method is used to reverse a string using stack
	public static String ReverseString(String str)
	{
	    // creating a empty character array
		char[] reverseString = new char[str.length()];
		// Now defining a stack of character data type
		Stack<Character> stack = new Stack<Character>();

		// Traversing the String from starting to end and pushing the character of the string parallely using the push() method
		for (int i = 0; i < str.length(); i++) {
			// push the character into the Stack
			stack.push(str.charAt(i));
		}
		// The insertion is done

        // Now removing the character from the stack using pop() function till the stack becomes empty
		int i = 0;
		while (!stack.isEmpty()) { // While loop runs till the stack becomes empty
			reverseString[i++] = stack.pop();
		}
		// return string object
		return new String(reverseString);
	}

	// Driver code
	public static void main(String[] args)
	{
	    System.out.println(" Hello, World! ");
	    // Creating an object to the Scanner class such that we can take the inputs from the user
	    Scanner sc = new Scanner(System.in);
	    System.out.println(" Enter a String: ");
	    // reading the String
	    String str = sc.next();
	    // printing the string
	    System.out.println(" The entered String is: " + str);
	    // printing the reverse String
	    System.out.println(" The String in reverse order is: " + ReverseString(str));
	}
}

Output:

Java Program to Reverse a String Using Stack

Time Complexity: O(n), where n is the Size of the String

Space Complexity: O(n), Extra space of the n size stack

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