SortArray3.java

/*
    SortArray3.java
    David G. Klick
    2/1/06
    CIS 260

This program demonstrates the use of a custom
    Comparator for changing the sort order. In this
    case, the Comparator simply changes the order to
    descending. It also uses a new feature of Java 1.5
    called Generics, which are similar to templates
    in C++.
*/

import java.util.*;

public class SortArray3 {
    public static void main(String[] args) {
        Comparator<Integer> desc = new DescendingComparator();
        Comparator<Integer> odds = new OddsFirstComparator();
        Integer[] n = { new Integer(8), new Integer(-8),
                        new Integer(13), new Integer(7),
                        new Integer(42), new Integer(5) };
        Arrays.sort(n, desc);
        System.out.print("Descending: ");
        for (int i : n) System.out.print(i + "  ");
        Arrays.sort(n, odds);
        System.out.print("\n\nOdds first: ");
        for (int i : n) System.out.print(i + "  ");
    }
}

/*
    This Comparator orders all Integers in
    descending numerical order.
*/
class DescendingComparator implements Comparator<Integer> {
    public int compare(Integer a, Integer b) {
        return b - a;
    }
}

/*
    This Comparator makes all odd numbers come
    before all even numbers. Within that order, the numbers
    are sorted by numerical value.
*/
class OddsFirstComparator implements Comparator<Integer> {
    public int compare(Integer a, Integer b) {
        boolean a_odd = a % 2 != 0;
        boolean b_odd = b % 2 != 0;
        if (a_odd && !b_odd) return -1;
        else if (!a_odd && b_odd) return 1;
        else return a - b;
    }
}

/*
    Sample run:

Descending: 42  13  8  7  5  -8

Odds first: 5  7  13  -8  8  42
*/