Palindrome String in Java: Understanding and Implementing Palindrome Checking

Welcome to this tutorial post on palindrome strings in Java! In this article, we will explore the concept of palindromes, discuss what they are, and how to write a Java program to determine if a given string is a palindrome or not. We will use the BlueJ programming language for demonstration purposes. So, let’s dive right in!

What is a Palindrome?

A palindrome refers to a word, phrase, number, or sequence of characters that maintains the same meaning when read forwards and backwards. In simpler terms, it remains unaltered even after its characters are reversed. For instance, words like “radar,” “madam,” and “level” exemplify palindromes.

↑

Understanding the Program: Comparing Characters Logic

To check whether a given string is a palindrome, we will follow a simple approach using Java. The program will compare the characters at corresponding positions from the start and end of the string to determine if it is a palindrome or not. If all the characters match, the string is a palindrome; otherwise, it is not.

Program Code

public class PalindromeChecker 
{
public static void main(String[] args) {
    String input = "radar";
    int i = 0;
    int j = input.length() - 1;
    boolean isPalindrome = true;

    while (i < j) {
        if (input.charAt(i) != input.charAt(j)) {
            isPalindrome = false;
            break;
        }

        i++;
        j--;
    }

    if (isPalindrome) {
        System.out.println(input + " is a palindrome.");
    } else {
        System.out.println(input + " is not a palindrome.");
    }
}
}
↑

Explanation of the Code

Let’s go through the code step by step to understand how it works:

  1. We start by defining a class called PalindromeChecker.
  2. Inside the class, we have the main method, which serves as the entry point of our program.
  3. We declare a variable called input and assign it the value “radar”. This is the string we want to check if it is a palindrome.
  4. Next, we declare and initialize two integer variables, i and j, with 0 and the length of the input string minus 1, respectively. These variables will be used to iterate through the string from both ends towards the middle.
  5. We also declare a boolean variable called isPalindrome and set it to true. This variable will help us determine whether the input string is a palindrome or not.
  6. We enter a while loop that continues until the value of i becomes greater than or equal to j. This loop allows us to compare characters from the start and end of the string towards the middle.
  7. Inside the loop, we use an if statement to check if the characters at positions i and j in the input string are different. If the characters at positions i and j are not equal, it indicates that the string does not qualify as a palindrome.
  8. In that case, we set the value of isPalindrome to false and exit the loop using the break statement.
  9. If the characters at positions i and j are equal, we increment i and decrement j to move on to the next pair of characters for comparison.
  10. After the loop finishes, we reach the end of the main method. Here, we use an if-else statement to check the value of the isPalindrome variable.
  11. If the value of isPalindrome is true, we print the message “radar is a palindrome.” This indicates that the input string “radar” is indeed a palindrome.
  12. If the value of isPalindrome is false, we print the message “radar is not a palindrome.” This indicates that the input string “radar” is not a palindrome.

And that’s it! The code efficiently determines whether a given string is a palindrome by comparing characters from both ends towards the middle.

↑

Palindrome String Checking in Java: Reversing the String Logic

An alternative approach to identifying palindrome strings is by comparing the original string with its reversed counterpart, instead of matching characters at corresponding positions. If the reversed string matches the original string, it signifies that the input is a palindrome.

Program Code

public class PalindromeChecker {
public static void main(String[] args) {
String input = "radar";
String reversedInput = "";   
 // Reversing the input string
    for (int i = input.length() - 1; i >= 0; i--) {
        reversedInput += input.charAt(i);
    }

    if (input.equals(reversedInput)) {
        System.out.println(input + " is a palindrome.");
    } else {
        System.out.println(input + " is not a palindrome.");
    }
}
}
↑

Explanation of the Code

  1. We start by defining a class called PalindromeChecker.
  2. Inside the class, we have the main method, which serves as the entry point of our program.
  3. We declare a variable called input and assign it the value “radar”. This is the string we want to check if it is a palindrome.
  4. We also declare an empty string called reversedInput. This variable will store the reversed form of the input string.
  5. Next, we use a for loop to iterate through the characters of the input string in reverse order.
  6. Inside the loop, we append each character to the reversedInput string, effectively reversing the original string.
  7. After the loop finishes, we use the equals method to compare the original input string with the reversedInput string.
  8. If the two strings are equal, we print the message “radar is a palindrome.” This indicates that the input string “radar” is indeed a palindrome.
  9. If the two strings are not equal, we print the message “radar is not a palindrome.” This indicates that the input string “radar” is not a palindrome.
↑

Conclusion

In this tutorial post, we explored the concept of palindrome strings in Java and discussed two different methods to check for palindromes. We examined the traditional approach of comparing characters at corresponding positions and the alternative approach of comparing the original string with its reversed form.

By leveraging the power of Java and the BlueJ programming language, we were able to demonstrate how to implement both methods and determine if a given string is a palindrome or not. Whether you choose to compare characters or compare the reversed string, both approaches provide effective ways to identify palindromes.

By utilizing the knowledge and code shared in this tutorial, you are now equipped with the tools to check for palindromes in Java. Feel free to explore further and experiment with different strings to deepen your understanding.

Happy coding!

↑