Java泛型&反射 [英] Java Generics & Reflection

问题描述

  Class myClass = Class.forName（整数）; 
 SomethingSimple< myClass> OBJ; 
  

其中SomethingSimple是一个简单的 泛型类：

  class SomethingSimple< T> 
 {
 T值; 
 SomethingSimple（）{} 
 public void setT（T val）
 {
 value = val; 
} 
 public T getT（）
 {
返回值; 
 
 
 $ / code> 

显然，上面的代码是不正确的，因为myClass是Class类型的对象，并且需要一个类。问题是如何实现这一点。我阅读了泛型反射的其他主题，但他们关心的是泛型类是如何知道类型的。

解决方案

使用Java中的泛型仅在编译时进行静态类型检查;类型检查后通用信息将被丢弃（请阅读类型擦除 ），所以在运行时， SomethingSimple< Foo> 实际上只是一个 SomethingSimple< Object> 。
$ b

当然，你不能对直到运行时才知道的类型进行补全时间类型检查。类型必须为编译器所知，这就是为什么你必须使用实际类型名称而不是 Class 变量作为泛型类型参数。

this probably is a basic question, but can I do something like this:

Class myClass = Class.forName("Integer");
SomethingSimple<myClass> obj;

Where SomethingSimple is a very simple generic class:

class SomethingSimple<T>
{
    T value;
    SomethingSimple() {}
    public void setT(T val)
    {
        value = val;
    }
    public T getT()
    {
        return value;
    }
}

Obviously, the code above is not correct, since myClass is an object of type Class, and a class is required. The question is how can this be achieved. I read the other topics about Generics Reflection, but they concerned how the generic class knows the type.

解决方案

Generics in Java are used only for static type checking at compile time; the generic information is discarded after type checking (read about type erasure) so a SomethingSimple<Foo> is effectively just a SomethingSimple<Object> at runtime.

Naturally, you can't do comple-time type checking on a type that isn't known until runtime. The type has to be known to the compiler, which is why you have to use an actual type name rather than a Class variable as the generic type parameter.

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