我如何知道泛型是Java中的一个类的实例？ [英] How do I find out if generic is instanceof a class in Java?

问题描述

我定义了以下类/子类。

  public class Vehicle 
 {
 } 
 
公共类车辆延伸车辆
 {
} 
 
公共类飞机延伸车辆
 {
} 
  

现在，我试图循环列出可以包含汽车和飞机的汽车记录列表。但是，我想弄清楚它是不是飞机记录（而不是汽车记录）。编译器告诉我错误：在检查实例上if（s instanceof Record< Aircraft>）的instanceof非法通用类型。我错过了什么？原谅我，我已经有数年没用过java了。

  for（Record<？extends Vehicle> s：rs.getResultReadOnly ））
 {
 if（s instanceof Record< Aircraft>）
 {
 ... 
} 
} 
  

解决方案

由于 type erasure ：通用信息< Aircraft>



然而你可以这样做：



  if（s.getVehicle（）instanceof Aircraft）{
 
} 
  




I have the following classes/sub-classes defined.

public class Vehicle
{
}

public class Car extends Vehicle
{
}

public class Aircraft extends Vehicle
{
}

Now, I'm trying to loop through a list of vehicle records where the list can contain cars and aircraft. But, I'd like to figure out if it's an aircraft record (and not a car record). The compiler is telling me "error: illegal generic type for instanceof if(s instanceof Record<Aircraft>)" on the instance of check. What am I missing? Forgive me, I haven't used java in years.

        for (Record<? extends Vehicle> s : rs.getResultReadOnly())
        {                    
            if(s instanceof Record<Aircraft>) 
            {
               ...
            }                    
        }

解决方案

You can't do this type of check because of type erasure: The generic information <Aircraft> will be lost at runtime.

However you can do something like this:

if (s.getVehicle() instanceof Aircraft) { 
  ..
}

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