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.
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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