If you are ask to use recursion to solve the palindrome exercise study this code.
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())…
}
}