来自类型变量的 Java 类对象
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原文地址: http://stackoverflow.com/questions/2801267/
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Java class object from type variable
提问by Alexander Temerev
Is there a way to get Class object from the type variable in Java generic class? Something like that:
有没有办法从 Java 泛型类中的类型变量中获取 Class 对象？类似的东西：
public class Bar extends Foo<T> {
public Class getParameterClass() {
return T.class; // doesn't compile
}
}
This type information is available at compile time and therefore should not be affected by type erasure, so, theoretically, there should be a way to accomplish this. Does it exist?
此类型信息在编译时可用，因此不应受到类型擦除的影响，因此，从理论上讲，应该有一种方法可以实现这一点。它存在吗？
采纳答案by sfussenegger
This works:
这有效：
public static class Bar extends Foo<String> {
public Class<?> getParameterClass() {
return (Class<?>) (((ParameterizedType)Bar.class.getGenericSuperclass()).getActualTypeArguments()[0]);
}
}
回答by tkr
The code snippet is a bit confusing. Is T a type parameter or a class?
代码片段有点混乱。T 是类型参数还是类？
public static class Bar extends Foo<String> {
public Class<?> getParameterClass() {
return (Class<?>) (((ParameterizedType)Bar.class.getGenericSuperclass()).getActualTypeArguments()[0]);
}
}
public static class Bar2<T> extends Foo<T> {
public Class<?> getParameterClass() {
return (Class<?>) (((ParameterizedType)Bar2.class.getGenericSuperclass()).getActualTypeArguments()[0]);
}
}
public static void main(String[] args) {
System.out.println(new Bar().getParameterClass());
System.out.println(new Bar2<Object>().getParameterClass());
}
Actually the second println will cause an exception.
实际上，第二个 println 会导致异常。
回答by Brad Parks
This code works for derived classes as well:
此代码也适用于派生类：
import java.lang.reflect.ParameterizedType;
public abstract class A<B>
{
public Class<B> getClassOfB() throws Exception
{
ParameterizedType superclass = (ParameterizedType) getClass().getGenericSuperclass();
return (Class<B>) superclass.getActualTypeArguments()[0];
}
}
snagged from here: https://stackoverflow.com/a/4699117/26510
