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Palindrome String in Java

By: Grant Braught in Java Tutorials on 2011年01月27日 [フレーム]

Checking if a String is a Palindrome is a common assignment given to Java students. This sample class is a helpful class that checks for various scenarios to find out if the given string is a palindrome.

public class Palindrome {
 private String pal;
 
 public Palindrome(String initPal) {
	pal = initPal.toUpperCase();
 }
 
 public boolean isPalindrome() {
 
	if (pal.length() <= 1) { // String has only one character so it // is a Palindrome by definition. return true; // BASE CASE. } // Get the first and last characters of the String. char first = pal.charAt(0); char last = pal.charAt(pal.length()-1); if (Character.isLetter(first) && Character.isLetter(last)) { // The first and last characters are both letters.. if (first != last) { // The first and last letters are different // so the string is not a Palindrome. return false; // BASE CASE. } else { // The first and last characters are both letters, // and they are both the same. So, the string is // a palindrome if the substring created by dropping // the first and last characters is a palindrome. Palindrome sub = new Palindrome( pal.substring(1,pal.length()-1)); return sub.isPalindrome(); // RECURSIVE CASE. } } else if (!Character.isLetter(first)) { // The first character in the string is not a letter. // So the string is a palindrome if the substring created // by dropping the first character is a palindrome. Palindrome sub = new Palindrome(pal.substring(1)); return sub.isPalindrome(); // RECURSIVE CASE. } else { // The last character in the string is not a letter. // So the string is a palindrome if the substring created // by dropping the last character is a palindrome. Palindrome sub = new Palindrome( pal.substring(0,pal.length()-1)); return sub.isPalindrome(); // RECURSIVE CASE. } } public static void main(String[] args) { Palindrome p1 = new Palindrome("Madam, I'm Adam."); System.out.println(p1.isPalindrome()); Palindrome p2 = new Palindrome("Nope!"); System.out.println(p2.isPalindrome()); Palindrome p3 = new Palindrome("dad"); System.out.println(p3.isPalindrome()); Palindrome p4 = new Palindrome("Go hang a salami, I'm a lasagna hog."); System.out.println(p4.isPalindrome()); } }

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