private <T> List<T> cashFutures(List<Future<T>> futures) {

        List<T> values = new ArrayList<T>();

        for (Future<T> future : futures) {
            try {
                values.add(future.get());
            } catch (Exception e) {
                throw new IllegalStateException(e);
            }
        }

        return values;
    }

import java.util.*;

class Fruit {     public String toString() {    return "Fruit"; } }

class Apple extends Fruit {    public String toString(){ return "Apple";    } }

class Person {    public String toString(){    return "Person";    } }

class ClassName<T> {//主类，把你文件名改成ClassName.java
     

     void show_1(T t){
        System.out.println("show_1  "+ t.toString());
    }
    
    <E> void show_2(E e){
        System.out.println("show_2  "+e.toString());
    }
    
    <T> void show_3(T t){
        System.out.println("show_3  "+t.toString());
    }
    
    

    public static void main(String[] args) {
        ClassName<Fruit> o = new ClassName<Fruit>();
        Fruit f = new Fruit();
        Apple a = new Apple();
        Person p = new Person();
        System.out.println("show_1 演示________________________");
        o.show_1( f );
        o.show_1( a );
//        o.show_1( p );  楼主把这行代码去掉注释看一下，是不能编译通过的。因为在
//        ClassName<Fruit>中已经限定了全局的T为Fruit，所以不能再加入Person;
        System.out.println("show_2 演示________________________");
        o.show_2( f );
        o.show_2( a );
        o.show_2( p );
        System.out.println("show_3 演示________________________");
        o.show_3( f );
        o.show_3( a );
        o.show_3( p );
        
    }
}
[color=#800080]程序输出：
show_1 演示________________________
show_1  Fruit
show_1  Apple
show_2 演示________________________
show_2  Fruit
show_2  Apple
show_2  Person
show_3 演示________________________
show_3  Fruit
show_3  Apple
show_3  Person[/color]