Java泛型方法

package PairTestMyCode.copy;
import java.util.*;
public class PairTest2
{
public static void main(String[] args)
{
GregorianCalendar[] birthdays =
{
new GregorianCalendar(1906, Calendar.DECEMBER, 9), // G. Hopper
new GregorianCalendar(1815, Calendar.DECEMBER, 10), // A. Lovelace
new GregorianCalendar(1903, Calendar.DECEMBER, 3), // J. von Neumann
new GregorianCalendar(1910, Calendar.JUNE, 22), // K. Zuse
};
Pair<GregorianCalendar> mm = ArrayAlg.minmax(birthdays);
System.out.println("min = " + mm.getFirst().getTime());
System.out.println("max = " + mm.getSecond().getTime());
}
}
class ArrayAlg
{
/**
Gets the minimum and maximum of an array of objects of type T.
@param a an array of objects of type T
@return a pair with the min and max value, or null if a is
null or empty
*/
public static <T extends Comparable> Pair<T> minmax(T[] a)
{
if (a == null || a.length == 0) return null;
T min = a[0];
T max = a[0];
for (int i = 1; i < a.length; i++)
{
if (min.compareTo(a[i]) > 0) min = a[i];
if (max.compareTo(a[i]) < 0) max = a[i];
}
return new Pair<T>(min, max);
}
}
class Pair<T>
{
private T first;
private T second;

public Pair()
{
first = null;
second = null;
}
public Pair(T first, T second)
{
this.first = first;
this.second = second;
}
public T getFirst()
{
return first;
}
public T getSecond()
{
return second;
}
public void setFirst(T newValue)
{
first = newValue;
}
public void setSecond(T newValue)
{
second = newValue;
}

}

 其中第30行代码是public static <T extends Comparable> Pair<T> minmax(T[] a)
{
if (a == null || a.length == 0) return null;
T min = a[0];
T max = a[0];
for