Java泛型有界类型参数

在java泛型中，有时候我们需限制泛型的类型，那么该如何操作呢？
下文笔者将一一道来，如下所示:
   如:对数字进行操作的方法可能只想接受Number或其子类的实例
   我们将这种限定称之为“有界的类型参数”

实现思路:
   有界类型需使用extends关键字

public class MaximumTest {
 
   public static <T extends Comparable<T>> T maximum(T x, T y, T z) {
      T max = x;   // assume x is initially the largest

      if(y.compareTo(max) > 0) {
         max = y;   // y is the largest so far
      }

      if(z.compareTo(max) > 0) {
         max = z;   // z is the largest now                 
      }
      return max;   // returns the largest object   
   }

   public static void main(String args[]) {
      System.out.printf("Max of %d, %d and %d is %d\n\n",
         3, 4, 5, maximum(3, 4, 5 ));

      System.out.printf("Max of %.1f,%.1f and %.1f is %.1f\n\n",
         6.6, 8.8, 7.7, maximum(6.6, 8.8, 7.7 ));

      System.out.printf("Max of %s, %s and %s is %s\n","pear",
         "apple", "orange", maximum("pear", "apple", "orange"));
   }
}

-----运行以上代码，将输出以下信息----
Max of 3, 4 and 5 is 5
Max of 6.6,8.8 and 7.7 is 8.8
Max of pear, apple and orange is pear