10 Best Way to Reverse a String in Java.

1) Using StringBuilder

public class StringReverseUsingStringBuilder {
    public static void main(String args[]){
         String reversed = new StringBuilder(str).reverse().toString();
        System.out.println("Reversed String :"+reversed);
    }
}

2) Using StringBuffer

Thread-safe alternative to StringBuilder.

public class StringReverseUsingStringBuffer {
    public static void main(String args[]){
        String str = "Hello World";
        String reversed = new StringBuffer(str).reverse().toString();
        System.out.println("Reversed string:"+reversed);
    }
}

3) Using Char Array Swapping (Optimized Manual Logic)

public class ReserseUsingCharArraySwapping {
    public static void main(String args[]){
        String str = "Hello World";
        char[] arr = str.toCharArray();
        int left=0;
        int right=arr.length-1;
        while(left<right){
            char temp=arr[left];
            arr[left]=arr[right];
            arr[right]=temp;
            left++;
            right--;
        }
        System.out.println("Reverse of String : "+new String(arr));
    }
}

4) Using For Loop + StringBuilder append().

public class ReverseStringUsingStringBuilderForLoop {
    public static void main(String args[]){
        String str = "Hello World";
        StringBuilder sb = new StringBuilder();
        for(int i=str.length()-1; i>=0; i--){
            sb.append(str.charAt(i));
        }
        System.out.println("Reversed String :"+sb.toString());
    }
}



5) Using For Loop + String Concatenation (Not Recommended, O(n²))
public class ReverseStringConcatenation {
    public static void main(String args[]){
        String str = "Hello World";
        String reversed = "";

        for (int i = str.length() - 1; i >= 0; i--) {
            reversed += str.charAt(i);
        }
        System.out.println("Reversed String:"+reversed);
    }
}


6) Using Recursion

public class StringReverseUsingRecursion {
    public static String reverse(String str) {
        if (str.isEmpty()) return str;
        return reverse(str.substring(1)) + str.charAt(0);
    }

    public static void main(String[] args) {
        System.out.println(reverse("Hello World"));
    }
}


7) Using Java 8 Streams

public class ReverseStringUsingJava8Streams {
    public static void main(String[] args) {
        String str = "Hello World";

        String reversed = str.chars()
                .mapToObj(c -> (char) c)
                .reduce("", (s, c) -> c + s, (s1, s2) -> s2 + s1);

        System.out.println("Reversed String :"+reversed);
    }
}



8) Using Collections.reverse()


import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class UsingCollecionReverse {
    public static void main(String[] args) {
        String str = "Hello World";
        List<Character> list = new ArrayList<>();
        for (char c : str.toCharArray()) {
            list.add(c);
        }
        Collections.reverse(list);
        StringBuilder sb = new StringBuilder();
        for (char c : list) {
            sb.append(c);
        }
        System.out.println(sb.toString());
    }
}


9) Using Stack
import java.util.Stack;

public class UsingStack {
    public static void main(String[] args) {
        String str = "Hello World";
        Stack<Character> stack = new Stack<>();
        for (char c : str.toCharArray()) {
            stack.push(c);
        }
        StringBuilder sb = new StringBuilder();
        while (!stack.isEmpty()) {
            sb.append(stack.pop());
        }
        System.out.println(sb.toString());
    }
}


10) Using XOR Swap (Interview Trick — Rare Use)

public class UsingXOrSwap {
    public static void main(String[] args) {
        String str = "Hello World";
        char[] arr = str.toCharArray();

        int left = 0, right = arr.length - 1;
        while (left < right) {
            arr[left] ^= arr[right];
            arr[right] ^= arr[left];
            arr[left] ^= arr[right];
            left++;
            right--;
        }

        System.out.println(new String(arr));
    }
}



🎯 PERFORMANCE SUMMARY



Method
Time Complexity
Space
Recommended
StringBuilder reverse()
O(n)
Low
⭐⭐⭐⭐⭐
Char swap array
O(n)
Low
⭐⭐⭐⭐⭐
StringBuffer reverse()
O(n)
Low
⭐⭐⭐⭐
Streams
O(n)
Medium
⭐⭐
Collections.reverse()
O(n)
High
⭐⭐
Recursion
O(n²)
High
⭐
String concat loop
O(n²)
High
❌ Avoid