comparator

//using comparators
public static void sort (Object[] a, Comparator comparator){
	int N = a.length;
	for (int i = 0; i<N; i++)
		for ( int j = i; j>0 && less(comparator, a[j], a[j-1]); j--)
			exch(a, j, j-1);
}
private static boolean less(Comparator c, Object v, Object w) {
	return c.compare(v,w) < 0;}
private static void exch(Object[]a, int i, int j){
	Object seap = a[i]; a[i]=a[j]; a[j]=swap;
}
//implement a comparator
public class Student {
	public static final Comparator<Student> BY_NAME = new ByName();
	public static final Comparator<Student> BY_SECTION = new BySection():
	private final String name;
	private final int section;
	private static class ByName implements Comparator<Student> {
		public int compare(Studetn v, Student w) {
			return v.name.compareTo(w.name); }
	}
	private static class BySection implements Comparator<Studetn> {
		public int compare(Student v, Student w) {
			return v.section - w.section;
		}
	}