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Summary of Characters and Strings

Use a Character object to contain a single character value, use a String object to contain a sequence of characters that won't change, and use a StringBuilder or StringBuffer object to construct or to modify a sequence of characters dynamically. Here's a fun program, Palindrome, that determines whether a string is a palindrome. This program uses many methods from the String and the StringBuilder classes:

public class Palindrome {

    public static boolean isPalindrome(String stringToTest) {
        String workingCopy = removeJunk(stringToTest);
        String reversedCopy = reverse(workingCopy);
        
        return reversedCopy.equalsIgnoreCase(workingCopy);
    }

    protected static String removeJunk(String string) {
        int i, len = string.length();
  	StringBuilder dest = new StringBuilder(len);
	char c;

	for (i = (len - 1); i >= 0; i--) {
	    c = string.charAt(i);
	    if (Character.isLetterOrDigit(c)) {
		dest.append(c);
	    }
	}

        return dest.toString();
    }

    protected static String reverse(String string) {
  	StringBuilder sb = new StringBuilder(string);

        return sb.reverse().toString();
    }

    public static void main(String[] args) {
        String string = "Madam, I'm Adam.";

        System.out.println();
        System.out.println("Testing whether the following "
                         + "string is a palindrome:");
        System.out.println("    " + string);
        System.out.println();

        if (isPalindrome(string)) {
            System.out.println("It IS a palindrome!");
        } else {
            System.out.println("It is NOT a palindrome!");
        }
        System.out.println();
    }
}

The output from this program is:

Testing whether the following string is a palindrome:
    Madam, I'm Adam.

It IS a palindrome!

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