Check palindrome string in java

In this tutorial we will write different solutions for palindrome string in java. In is one of the questions asked in interviews.

What is a palindrome?

A palindrome is a word, phrase, number or other sequence of units that can be read the same way in either direction. Here is an example of palindrome string.

Palindrome String in Java

Palindrome String

Write a program to check palindrome string in java

/**
 * 
 * @author programtalk.com
 *
 */
public class CheckPalindrome {
	boolean isPalindrome(String input) {
		int stringLength = input.length();
		int indexLastElement = stringLength -1;
		for (int i = 0; i < stringLength / 2; i++) {
			if (input.charAt(i) != input.charAt(indexLastElement - i)) {
				return false;
			}
		}
		return true;
	}

	public static void main(String[] args) {
		CheckPalindrome checkPalindrom = new CheckPalindrome();
		System.out.println("madam is plaindrome : " +checkPalindrom.isPalindrome("madam"));
		System.out.println("running is palindrome : "+checkPalindrom.isPalindrome("running"));
	}
}

Output

madam is plaindrome : true
running is palindrome : false

Check Palindrome using StringBuilder.reverse()

/**
 * 
 * @author programtalk.com
 *
 */
public class CheckPalindrome {
	boolean isPalindrome(String input) {
		return input.equals(new StringBuilder(input).reverse().toString());

	}

	public static void main(String[] args) {
		CheckPalindrome checkPalindrom = new CheckPalindrome();
		System.out.println("madam is plaindrome : " + checkPalindrom.isPalindrome("madam"));
		System.out.println("running is palindrome : " + checkPalindrom.isPalindrome("running"));
	}
}

StringBuilder().reverse() reverses the String and then checking for equality does the palindrom check. But this solution is not very efficient, for more see here

Note :  Instances of StringBuilder are not safe for use by multiple threads. If such synchronization is required then it is recommended that StringBuffer be used.

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