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Java Program to Reverse a String using Stack

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The Stack is a linear data structure that follows the LIFO(Last In First Out) principle, i.e, the element inserted at the last is the element to come out first.


  1. Push the character one by one into the Stack of datatype character.
  2. Pop the character one by one from the Stack until the stack becomes empty.
  3. Add a popped element to the character array.
  4. Convert character array to string.
  5. Return reversed string.

Below is the implementation of the above approach.


// Java Program to Reverse a String using Stack
import java.util.*;
class GFG {
    public static String ReverseString(String str)
        char[] reverseString = new char[str.length()];
        // Declare a stack of type Character
        Stack<Character> stack = new Stack<Character>();
        // Traverse the String and push the character one by
        // one into the Stack
        for (int i = 0; i < str.length(); i++) {
            // push the character into the Stack
        // Now Pop the Characters from the stack until it
        // becomes empty
        int i = 0;
        while (!stack.isEmpty()) { // popping element until
                                   // stack become empty
            // get the character from the top of the stack
            reverseString[i++] = stack.pop();
        // return string object
        return new String(reverseString);
    // Driver code
    public static void main(String[] args)
        String str1 = "GeeksForGeeks";
        // call the function
        System.out.println(str1 + " <- Reverse -> "
                           + ReverseString(str1));
        String str2 = "Hello World";
        // call the function
        System.out.println(str2 + " <- Reverse -> "
                           + ReverseString(str2));


GeeksForGeeks <- Reverse -> skeeGroFskeeG
Hello World <- Reverse -> dlroW olleH

Time Complexity: O(n), where n is a number of characters in the stack.

Auxiliary Space: O(n) for the stack.

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Last Updated : 21 Oct, 2020
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