10 Fundamental Classes

/**
 * Aggregate pairs of arbitrary objects.
 */
public final class Pair {
    private Object first, second;

    /** Construct a Pair object. */
    public Pair(Object one, Object two) {
        first = one;
        second = two;
    }

    /** Provides access to the first aggregated object. */
    public Object getFirst() { return first; }

    /** Provides access to the second aggregated object. */
    public Object getSecond() { return second; }

    /** @return true if the pair of objects are identical. */
    public boolean equals(Object other) {
        if (! (other instanceof Pair)) return false;
        Pair otherPair = (Pair) other;
        return first.equals(otherPair.getFirst()) &&
               second.equals(otherPair.getSecond());
    }

    /** @return a hash code for the aggregate pair. */
    public int hashCode() {
        // XORing the hash codes to create a hash code for the pair.
        return first.hashCode() ^ second.hashCode();
    }

    /** @return the textual representation of aggregated objects. */
    public String toString() {
        return "[" + first + "," + second + "]";
    }
}

public class Palindrome {
    public static void main(String[] args) {
        if (args.length != 1) {
            System.out.println("Usage: java Palindrome <word>");
            return;
        }
        String word = args[0];
        StringBuffer reverseWord = new StringBuffer(word);
        reverseWord.reverse();
        boolean isPalindrome = word.equals(reverseWord.toString());

        System.out.println("The word " + word + " is " +
                            (isPalindrome ? "" : "not ") +
                            "a palindrome");
    }
}