类型参数可以具有多个边界。

Multiple Bounds - 语法

public static <T extends Number & Comparable<T>> T maximum(T x, T y, T z)

  • maximum - 是一种泛型方法。

  • T                 - 传递的参数，它可以带任何对象。

T是传递给泛型类Box的类型参数，并且应该是Number类的子类型，并且必须包含Comparable接口。

package com.learnfk;

public class GenericsTester {
   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 ));
   }

   public static <T extends Number 
      & Comparable<T>> T maximum(T x, T y, T z) {
      T max=x;      
      if(y.compareTo(max) > 0) {
         max=y;   
      }

      if(z.compareTo(max) > 0) {
         max=z;                    
      }
      return max;      
   }

   //编译器在以下声明的情况下抛出错误
   /* public static <T extends Comparable<T> 
      & Number> T maximum1(T x, T y, T z) {
      T max=x;      
      if(y.compareTo(max) > 0) {
         max=y;   
      }

      if(z.compareTo(max) > 0) {
         max=z;                    
      }
      return max;   
   }*/
}

这将产生以下输出-

Max of 3, 4 and 5 is 5

Max of 6.6,8.8 and 7.7 is 8.8

参考链接

https://www.learnfk.com/java-generics/java-generics-multiple-bounds.html