无涯教程-Java泛型 - 上界通配符

问号("marked">extends关键字，然后是其上限。

以下示例说明了如何使用extends来指定上限通配符。

package com.learnfk;

import java.util.Arrays;
import java.util.List;

public class GenericsTester {

   public static double sum(List<"pln"> extends Number> numberlist) {
      double sum = 0.0;
      for (Number n : numberlist) sum += n.doubleValue();
      return sum;
   }

   public static void main(String args[]) {
      List<Integer> integerList = Arrays.asList(1, 2, 3);
      System.out.println("sum=" + sum(integerList));

      List<Double> doubleList = Arrays.asList(1.2, 2.3, 3.5);
      System.out.println("sum=" + sum(doubleList));
   }
}

这将产生以下输出 -

sum=6.0
sum=7.0

参考链接

https://www.learnfk.com/java-generics/java-generics-upper-bounded.html