Java Program to Check Whether a String is a Palindrome
Last Updated :
12 Jul, 2025
A string in Java can be called a palindrome if we read it from forward or backward, it appears the same or in other words, we can say if we reverse a string and it is identical to the original string for example we have a string s = "jahaj " and when we reverse it s = "jahaj"(reversed) so they look identical so we can say that "jahaj" is a palindrome string. In this article, we will go through different approaches to check if a string is a palindrome in Java.
Example Input/Output:
Input: s = "level"
Output: True
Input: s = "Geeks"
Output: True
Input s = "G"
Output: True.
Brute Force Approach
The brute force or naive approach to check if a string is a palindrome is by reversing the string, and then we can compare it with the original. Here, to ensure the comparison is case-insensitive, the string is converted to lowercase before the check. For example, if we do not convert the string to lowercase so it won't work with the different cases, such as Level and level, it will give false, but it is a palindrome.
Algorithm:
- First, convert the string to lowercase to ensure a case-insensitive comparison.
- Reverse the string using a loop.
- Compare the original string with the reversed String. If both are equal, then it is a palindrome. Otherwise, it is not.
Example: Java program to check whether a string is a palindrome by comparing it with its reversed string.
Java
// Java Program to Check if a
// String is a Palindrome
import java.io.*;
public class Geeks
{
// Method to check if a string is a palindrome
public static boolean isPalindrome(String s) {
// Convert string to lowercase for
// case-insensitive comparison
s = s.toLowerCase();
// Reverse the string
String rev = "";
for (int i = s.length() - 1; i >= 0; i--) {
rev = rev + s.charAt(i);
}
// Compare the original string with
// the reversed string
return s.equals(rev);
}
public static void main(String[] args) {
// Input string
String s = "level";
// Check if the string is a palindrome
boolean res = isPalindrome(s);
// Print the result with enhanced output
if (res) {
System.out.println('"' + s + '"' + " is a palindrome.");
} else {
System.out.println('"' + s + '"' + " is not a palindrome.");
}
}
}
Output"level" is a palindrome.
Explanation: In the above example, It checks if the given string is palindrome by converting it to lowercase, reversing it, and then comparing the reversed string with the original.
- Time Complexity: O(n)
- Space Complexity: O(n)
Other Methods to Check a String Palindrome
1. Two Pointer Approach to Check if incrementa String Is Palindrome
This approach uses two pointers, one starting at the beginning "i" and the other at the end "j" of the string. By comparing characters at these pointers and moving them inward, we can determine if the string is a palindrome or not.
Algorithm:
- We initialize two pointers (i=0) from the start and (j = s.length -1) from the end.
- Compare the characters at index i and j, if both are not equal then return false( it is not a palindrome).
- If they match then increment i by 1 and decrement j by 1 and continue the process.
- If all the characters match and the loop stops at ( i = j), then it is a palindrome and returns true.
Example:
Java
// Java program to check whether a
// string is a Palindrome
// Using two pointing variables
public class Geeks
{
// Method to check if a string is a palindrome
public static boolean isPalindrome(String s) {
int i = 0, j = s.length() - 1;
// Compare characters while i < j
while (i < j) {
if (s.charAt(i) != s.charAt(j)) {
return false;
}
i++;
j--;
}
return true;
}
public static void main(String[] args) {
// Input strings
String s1 = "geeks";
String s2 = "Racecar";
// Convert strings to lowercase for
// case-insensitive comparison
s1 = s1.toLowerCase();
s2 = s2.toLowerCase();
// Check and print results for s1
if (isPalindrome(s1)) {
System.out.println("\"" + s1 + "\" is a palindrome.");
} else {
System.out.println("\"" + s1 + "\" is not a palindrome.");
}
// Check and print results for s2
if (isPalindrome(s2)) {
System.out.println("\"" + s2 + "\" is a palindrome.");
} else {
System.out.println("\"" + s2 + "\" is not a palindrome.");
}
}
}
Output"geeks" is not a palindrome.
"racecar" is a palindrome.
Explanation: In this example, the isPalindrome method checks for mismatched characters while i < j and returns false if found. The main method converts input strings to lowercase and prints whether they are palindrome.
- Time Complexity: O(n)
- Space Complexity: O(1)
2. Recursive Approach to Check if a String is Palindrome
Now for recursion we are using the same approach as we used in the two pointer, here we create two pointer I from start and j from the end in the recursion. and Increaement the i by one and decrement j by 1, if the characters at the index i not match the character present at index j then it is not a palidrome if it the base condition hit i=j and
Algorithm:
- We will take two pointers, "i" pointing to the start of the string and "j" pointing to the end of the string.
- Base Case: If i >= j, the recursion stops, as the string has been fully checked, and it is confirmed to be a palindrome.
- Character Comparison: Check if the characters at positions i and j are equal.
- If not, return false immediately (the string is not a palindrome).
- If they match, make a recursive call with the next set of indices (i + 1 and j - 1).
- The recursion continues until the base case is satisfied.
If all characters match until the pointers meet or cross, the string is a palindrome. Otherwise, it is not.
Example:
Java
// Java program to check whether a
// string is a Palindrome using recursion
public class Geeks
{
// Recursive method to check
// if a string is a palindrome
public static boolean isPalindrome(int i, int j, String s) {
// If pointers have crossed,
// it's a palindrome
if (i >= j) {
return true;
}
// If characters at i and j are not the same,
// return false
if (s.charAt(i) != s.charAt(j)) {
return false;
}
// Recursive call for the
//next pair of pointers
return isPalindrome(i + 1, j - 1, s);
}
// Overloaded method to simplify the call
public static boolean isPalindrome(String s) {
return isPalindrome(0, s.length() - 1, s);
}
public static void main(String[] args) {
// Input strings
String s1 = "geeks";
String s2 = "Racecar";
// Convert strings to lowercase for
// case-insensitive comparison
s1 = s1.toLowerCase();
s2 = s2.toLowerCase();
// Check and print results for s1
if (isPalindrome(s1)) {
System.out.println("\"" + s1 + "\" is a palindrome.");
} else {
System.out.println("\"" + s1 + "\" is not a palindrome.");
}
// Check and print results for s2
if (isPalindrome(s2)) {
System.out.println("\"" + s2 + "\" is a palindrome.");
} else {
System.out.println("\"" + s2 + "\" is not a palindrome.");
}
}
}
Output"geeks" is not a palindrome.
"racecar" is a palindrome.
- Time Complexity: O(n)
- Space Complexity: O(n)
3. StringBuilder Approach to Check a String is Palindrome
In this approach, we will use the StringBuilder class to reverse a string and compare it with the original string. Below are the steps:
- First we create an object of StringBuilder using the input string.
- Then we use the reverse() method of StringBuilder class to reverse the string.
- Now, convert the reversed string back to a String using the method toString().
- Compare the reversed string with the original string using the equals() method.
- If the equals method returns true then it is a palindrome otherwise it is a not a palindrome.
Example:
Java
// Java program to check if a
// string is a palindrome using StringBuilder
public class Geeks
{
public static void main(String[] args) {
// Input string
String s = "GeeksForGeeks";
// Create a StringBuilder object
//with the original string
StringBuilder s1 = new StringBuilder(s);
// Reverse the string
// using the reverse() method
s1.reverse();
// Compare the reversed string
// with the original string
if (s.equals(s1.toString())) {
System.out.println("\"" + s + "\" is a palindrome string.");
} else {
System.out.println("\"" + s + "\" is not a palindrome string.");
}
}
}
Output"GeeksForGeeks" is not a palindrome string.
- Time Complexity: O(n)
- Space Complexity: O(n)
Similar Reads
Java Tutorial Java is a high-level, object-oriented programming language used to build web apps, mobile applications, and enterprise software systems. Known for its Write Once, Run Anywhere capability, which means code written in Java can run on any device that supports the Java Virtual Machine (JVM).Syntax and s
10 min read
Basics
Introduction to JavaJava is a high-level, object-oriented programming language developed by Sun Microsystems in 1995. It is platform-independent, which means we can write code once and run it anywhere using the Java Virtual Machine (JVM). Java is mostly used for building desktop applications, web applications, Android
4 min read
Java Programming BasicsJava is one of the most popular and widely used programming language and platform. A platform is an environment that helps to develop and run programs written in any programming language. Java is fast, reliable and secure. From desktop to web applications, scientific supercomputers to gaming console
4 min read
Java MethodsJava Methods are blocks of code that perform a specific task. A method allows us to reuse code, improving both efficiency and organization. All methods in Java must belong to a class. Methods are similar to functions and expose the behavior of objects.Example: Java program to demonstrate how to crea
7 min read
Access Modifiers in JavaIn Java, access modifiers are essential tools that define how the members of a class, like variables, methods, and even the class itself, can be accessed from other parts of our program. They are an important part of building secure and modular code when designing large applications. In this article
6 min read
Arrays in JavaIn Java, an array is an important linear data structure that allows us to store multiple values of the same type. Arrays in Java are objects, like all other objects in Java, arrays implicitly inherit from the java.lang.Object class. This allows you to invoke methods defined in Object (such as toStri
9 min read
Java StringsIn Java, a String is the type of object that can store a sequence of characters enclosed by double quotes and every character is stored in 16 bits, i.e., using UTF 16-bit encoding. A string acts the same as an array of characters. Java provides a robust and flexible API for handling strings, allowin
8 min read
Regular Expressions in JavaIn Java, Regular Expressions or Regex (in short) in Java is an API for defining String patterns that can be used for searching, manipulating, and editing a string in Java. Email validation and passwords are a few areas of strings where Regex is widely used to define the constraints. Regular Expressi
7 min read
OOPs & Interfaces
Classes and Objects in JavaIn Java, classes and objects are basic concepts of Object Oriented Programming (OOPs) that are used to represent real-world concepts and entities. A class is a template to create objects having similar properties and behavior, or in other words, we can say that a class is a blueprint for objects.An
10 min read
Java ConstructorsIn Java, constructors play an important role in object creation. A constructor is a special block of code that is called when an object is created. Its main job is to initialize the object, to set up its internal state, or to assign default values to its attributes. This process happens automaticall
10 min read
Java OOP(Object Oriented Programming) ConceptsBefore Object-Oriented Programming (OOPs), most programs used a procedural approach, where the focus was on writing step-by-step functions. This made it harder to manage and reuse code in large applications.To overcome these limitations, Object-Oriented Programming was introduced. Java is built arou
10 min read
Java PackagesPackages in Java are a mechanism that encapsulates a group of classes, sub-packages and interfaces. Packages are used for: Prevent naming conflicts by allowing classes with the same name to exist in different packages, like college.staff.cse.Employee and college.staff.ee.Employee.They make it easier
8 min read
Java InterfaceAn Interface in Java programming language is defined as an abstract type used to specify the behaviour of a class. An interface in Java is a blueprint of a behaviour. A Java interface contains static constants and abstract methods. Key Properties of Interface:The interface in Java is a mechanism to
11 min read
Collections
Exception Handling
Java Exception HandlingException handling in Java is an effective mechanism for managing runtime errors to ensure the application's regular flow is maintained. Some Common examples of exceptions include ClassNotFoundException, IOException, SQLException, RemoteException, etc. By handling these exceptions, Java enables deve
8 min read
Java Try Catch BlockA try-catch block in Java is a mechanism to handle exceptions. This make sure that the application continues to run even if an error occurs. The code inside the try block is executed, and if any exception occurs, it is then caught by the catch block.Example: Here, we are going to handle the Arithmet
4 min read
Java final, finally and finalizeIn Java, the keywords "final", "finally" and "finalize" have distinct roles. final enforces immutability and prevents changes to variables, methods, or classes. finally ensures a block of code runs after a try-catch, regardless of exceptions. finalize is a method used for cleanup before an object is
4 min read
Chained Exceptions in JavaChained Exceptions in Java allow associating one exception with another, i.e. one exception describes the cause of another exception. For example, consider a situation in which a method throws an ArithmeticException because of an attempt to divide by zero.But the root cause of the error was an I/O f
3 min read
Null Pointer Exception in JavaA NullPointerException in Java is a RuntimeException. It occurs when a program attempts to use an object reference that has the null value. In Java, "null" is a special value that can be assigned to object references to indicate the absence of a value.Reasons for Null Pointer ExceptionA NullPointerE
5 min read
Exception Handling with Method Overriding in JavaException handling with method overriding in Java refers to the rules and behavior that apply when a subclass overrides a method from its superclass and both methods involve exceptions. It ensures that the overridden method in the subclass does not declare broader or new checked exceptions than thos
4 min read
Java Advanced
Java Multithreading TutorialThreads are the backbone of multithreading. We are living in the real world which in itself is caught on the web surrounded by lots of applications. With the advancement in technologies, we cannot achieve the speed required to run them simultaneously unless we introduce the concept of multi-tasking
15+ min read
Synchronization in JavaIn multithreading, synchronization is important to make sure multiple threads safely work on shared resources. Without synchronization, data can become inconsistent or corrupted if multiple threads access and modify shared variables at the same time. In Java, it is a mechanism that ensures that only
10 min read
File Handling in JavaIn Java, with the help of File Class, we can work with files. This File Class is inside the java.io package. The File class can be used to create an object of the class and then specifying the name of the file.Why File Handling is Required?File Handling is an integral part of any programming languag
6 min read
Java Method ReferencesIn Java, a method is a collection of statements that perform some specific task and return the result to the caller. A method reference is the shorthand syntax for a lambda expression that contains just one method call. In general, one does not have to pass arguments to method references.Why Use Met
9 min read
Java 8 Stream TutorialJava 8 introduces Stream, which is a new abstract layer, and some new additional packages in Java 8 called java.util.stream. A Stream is a sequence of components that can be processed sequentially. These packages include classes, interfaces, and enum to allow functional-style operations on the eleme
15+ min read
Java NetworkingWhen computing devices such as laptops, desktops, servers, smartphones, and tablets and an eternally-expanding arrangement of IoT gadgets such as cameras, door locks, doorbells, refrigerators, audio/visual systems, thermostats, and various sensors are sharing information and data with each other is
15+ min read
JDBC TutorialJDBC stands for Java Database Connectivity. JDBC is a Java API or tool used in Java applications to interact with the database. It is a specification from Sun Microsystems that provides APIs for Java applications to communicate with different databases. Interfaces and Classes for JDBC API comes unde
12 min read
Java Memory ManagementJava memory management is the process by which the Java Virtual Machine (JVM) automatically handles the allocation and deallocation of memory. It uses a garbage collector to reclaim memory by removing unused objects, eliminating the need for manual memory managementJVM Memory StructureJVM defines va
4 min read
Garbage Collection in JavaGarbage collection in Java is an automatic memory management process that helps Java programs run efficiently. Java programs compile to bytecode that can be run on a Java Virtual Machine (JVM). When Java programs run on the JVM, objects in the heap are created, which is a portion of memory dedicated
7 min read
Memory Leaks in JavaIn programming, a memory leak happens when a program keeps using memory but does not give it back when it's done. It simply means the program slowly uses more and more memory, which can make things slow and even stop working. Working of Memory Management in JavaJava has automatic garbage collection,
3 min read
Practice Java
Java Interview Questions and AnswersJava is one of the most popular programming languages in the world, known for its versatility, portability, and wide range of applications. Java is the most used language in top companies such as Uber, Airbnb, Google, Netflix, Instagram, Spotify, Amazon, and many more because of its features and per
15+ min read
Java Programs - Java Programming ExamplesIn this article, we will learn and prepare for Interviews using Java Programming Examples. From basic Java programs like the Fibonacci series, Prime numbers, Factorial numbers, and Palindrome numbers to advanced Java programs.Java is one of the most popular programming languages today because of its
8 min read
Java Exercises - Basic to Advanced Java Practice Programs with SolutionsLooking for Java exercises to test your Java skills, then explore our topic-wise Java practice exercises? Here you will get 25 plus practice problems that help to upscale your Java skills. As we know Java is one of the most popular languages because of its robust and secure nature. But, programmers
7 min read
Java Quiz | Level Up Your Java SkillsThe best way to scale up your coding skills is by practicing the exercise. And if you are a Java programmer looking to test your Java skills and knowledge? Then, this Java quiz is designed to challenge your understanding of Java programming concepts and assess your excellence in the language. In thi
1 min read
Top 50 Java Project Ideas For Beginners and Advanced [Update 2025]Java is one of the most popular and versatile programming languages, known for its reliability, security, and platform independence. Developed by James Gosling in 1982, Java is widely used across industries like big data, mobile development, finance, and e-commerce.Building Java projects is an excel
15+ min read