Java Basics
Before understanding a string reverse program in java, you should know:
- What a String is
- How loops work
- How methods are called
- Immutable nature of Java Strings
Strings in Java are immutable, meaning they cannot be changed once created—this is why most reverse operations create a new string.
OOP & Interfaces
In Java, string reversal can be implemented using:
- Classes (String, StringBuilder, StringBuffer)
- Interfaces (List, Deque)
- Utility classes (Collections)
Understanding OOP helps you choose the right approach based on performance and readability.
Collections
Collections allow string reversal using:
- Lists
- Stacks
- Utility methods like Collections.reverse()
These methods are helpful when working with complex data structures.
Exception Handling
Always validate input when writing a string reverse program in java:
- Handle null values
- Avoid Index Out Of Bounds Exception
- Validate user input length
Java Advanced
Advanced concepts include:
- Java 8 Streams
- Lambda expressions
- Recursion optimization
- Stack-based solutions
Practice Java
Practicing multiple variations of string reversal improves:
- Logical thinking
- Interview readiness
- Understanding of time and space complexity
Reverse a String in Java
Below are the most commonly asked and interview-relevant approaches.
1. Using a For Loop
(string reverse program in java using for loop)
public class ReverseString {
public static void main(String[] args) {
String str = “Java”;
String reversed = “”;
for (int i = str.length() – 1; i >= 0; i–) {
reversed += str.charAt(i);
}
System.out.println(reversed);
}
}
✔ Beginner-friendly
❌ Less efficient due to string immutability
2. Using StringBuilder.reverse()
(string reverse program in java)
String str = “Java”;
String reversed = new StringBuilder(str).reverse().toString();
System.out.println(reversed);
✔ Fast
✔ Recommended approach
3. Using Character Array
char[] chars = str.toCharArray();
for (int i = chars.length – 1; i >= 0; i–) {
System.out.print(chars[i]);
}
✔ Efficient
✔ Low memory overhead
4. Using Collections.reverse()
List<Character> list = new ArrayList<>();
for (char c : str.toCharArray()) {
list.add(c);
}
Collections.reverse(list);
✔ Useful with collections
❌ Overkill for simple reversal
5. Using StringBuffer.reverse()
StringBuffer sb = new StringBuffer(“Java”);
System.out.println(sb.reverse());
✔ Thread-safe
✔ Simple syntax
6. Using a Stack
Stack<Character> stack = new Stack<>();
for (char c : str.toCharArray()) stack.push(c);
while (!stack.isEmpty()) System.out.print(stack.pop());
✔ Good for learning data structures
❌ Slower than StringBuilder
7. Using getBytes()
byte[] bytes = str.getBytes();
for (int i = bytes.length – 1; i >= 0; i–) {
System.out.print((char) bytes[i]);
}
✔ Low-level approach
❌ Rarely used in practice
String Reverse Program in Java Using Recursion
public static String reverse(String str) {
if (str.isEmpty()) return str;
return reverse(str.substring(1)) + str.charAt(0);
}
✔ Conceptually strong
❌ Not memory-efficient
String Reverse Program in Java 8
String reversed = new StringBuilder(str).reverse().toString();
Java 8 doesn’t add a new reverse API, but encourages cleaner, functional-style coding.
String Reverse Program in JavaScript
let str = “Java”;
let reversed = str.split(”).reverse().join(”);
console.log(reversed);
✔ One-liner
✔ Very popular in web interviews
When to Use Which Method
| Scenario | Best Method |
| Interviews | For loop / Recursion |
| Production code | StringBuilder |
| Thread safety | StringBuffer |
| Data structure practice | Stack |
| JavaScript apps | split-reverse-join |
FAQs
1. What is the best string reverse program in Java?
Using StringBuilder.reverse() is the fastest and most recommended approach.
2. Is recursion good for reversing strings in Java?
Recursion is useful for learning but not recommended for large strings due to memory overhead.
3. Can we reverse a string without using built-in methods?
Yes, using loops, recursion, or stacks.
4. Is string reversal asked in Java interviews?
Yes, it’s one of the most common beginner-to-intermediate Java interview questions.
Conclusion
The string reverse program in java is a foundational problem that teaches loops, recursion, immutability, and data structures. Whether you’re a beginner or preparing for interviews, mastering multiple approaches helps you write cleaner, more efficient Java code.