Week 9 - Loop Example

Loop Example

Write a boolean method that determines if the String passed to the method is a palindrome (spelled the same backwards and forwards - e.g. tot).

Sample input:

   tot
   everything
   hello
   abcba
   abba
   XXX

Sample output:

   true
   false
   false
   true
   true

Java program

// Programmer: Andria Hunter
// Date:       July 10, 2001
// Course:     CSC108
//
// PalinChecker: this class is used to determine which lines of input
//               are palindromes.
//
import java.io.*;
class PalinChecker {

	/**
	* main: This method is where the program starts execution.  It
	* reads input from the user and then prints out true or false
	* to indicate whether each line of input is a palindrome.
	*/
	public static void main (String[] args) throws IOException {

		BufferedReader in = new BufferedReader(new InputStreamReader
			(System.in));

		final String STOPPER = "XXX";	// stop when this is entered

		// Each iteration of this loop reads in one line of input from
		// the user and calls the isPalindrome method to print out
		// whether or not the line is a palindrome.
		while (true) {

	 		String line = in.readLine();
	 		if (line.equals(STOPPER)) {
				break;
			}

			System.out.println (isPalindrome (line));
		}
	}

	/**
	* isPalindrome: this method returns true iff 's' is a palindrome,
	* i.e. it has the same sequence of letters when it is read from the
	* left to the right as when it is read from the right to the left.
	* Precondition: s may not be null.
	*/
	private static boolean isPalindrome (String s) {
		for (int i=0; i<s.length()/2; i++) {
			if (s.charAt(i) != s.charAt(s.length()-1-i)) {
				return false;
			}
		}
		return true;
	}
}