Java – class with multiple bounded types and unchecked casts asSubclass

I have a class of type < T extends enum < T >& Ampere; Operational replacement I have a member variable class < T > the column I set by class name: T = (class < T >) class forName(name). This gave me an unchecked projection warning

Generally, using assubclass can be used in similar situations, but because t has multiple boundaries, I can't use it without getting a compiler warning:

//This is type safe,but I still get an unchecked cast warning
t = (Class<T>) Class.forName(className).asSubclass(Enum.class).asSubclass(Runnable.class);@H_403_5@ 
 
我可以在不使用@SupressedWarning(“未选中”)的情况下以任何方式摆脱此警告吗？
 
 
完整示例：
 
  
 
public class Example<T extends Enum<T> & Runnable> {
    Class<T> t;

    Example(String className) throws ClassNotFoundException {
        t = (Class<T>) Class.forName(className).asSubclass(Enum.class).asSubclass(Runnable.class);
    }
}@H_403_5@

Solution
//This is type safe,but I still get an unchecked cast warning
//This is type safe,but I still get an unchecked cast warning
t = (Class<T>) Class.forName(className).asSubclass(Enum.class).asSubclass(Runnable.class);@H_403_5@ 
 
哇,放慢一秒！这是真的吗？不,这不对！你所做的就是确定匹配传入名称的类是Runnable和Enum,而不是它实际上是T.你只验证了边界.想象一下,我们有T1和T2类：
 
  
 
package foo;
public enum T1 implements Runnable {
    ;
    @Override
    public void run() {
    }
}

package foo;
public enum T2 implements Runnable {
    ;
    @Override
    public void run() {
    }
}@H_403_5@ 
 
然后这工作正常,但显然不是类型安全的：
 
  
 
Example<T1> example = new Example<T1>("foo.T2");
Class<T1> t1Clazz = example.t; //uh oh...@H_403_5@ 
 
这也不是多重边界的问题.你只有一个绑定你有同样的问题.
 
 
正如@ sp00m所提到的,真正的解决方案可能是传递给Class< T>这里.
 
 
编辑
 
 
另一方面,如果仅在内部需要T(即指定多个边界)并且实际上不需要暴露,则另一个选择是将类保持在两个单独的引用中.例如：
 
  
 
Class<? extends Runnable> runnableClass;
Class<? extends Enum> enumClass;

Example(String className) throws ClassNotFoundException,illegalaccessexception,InstantiationException {
    Class<?> clazz = Class.forName(className);
    runnableClass = clazz.asSubclass(Runnable.class);
    enumClass = clazz.asSubclass(Enum.class);
}@H_403_5@ 
 
这是因为,如果没有类型参数,在极少数情况下您可以实际利用它的同时知道枚举和Runnable的知识.如果创建类的实例,则需要将其分配给Runnable或Enum类型的变量/字段;你不能两者兼顾.