How to determine the class of a generic type?

Question

I'm creating a generic class and in one of the methods I need to know the Class of the generic type currently in use. The reason is that one of the method's I call expects this as an argument.

Example:

public class MyGenericClass<T> {   public void doSomething() {     // Snip...     // Call to a 3rd party lib     T bean = (T)someObject.create(T.class);     // Snip...   } } 

Clearly the example above doesn't work and results in the following error: Illegal class literal for the type parameter T.

My question is: does someone know a good alternative or workaround for this?

Answer 1

Still the same problems : Generic informations are erased at runtime, it cannot be recovered. A workaround is to pass the class T in parameter of a static method :

public class MyGenericClass<T> {      private final Class<T> clazz;      public static <U> MyGenericClass<U> createMyGeneric(Class<U> clazz) {         return new MyGenericClass<U>(clazz);     }      protected MyGenericClass(Class<T> clazz) {         this.clazz = clazz;     }      public void doSomething() {         T instance = clazz.newInstance();     } } 

It's ugly, but it works.

Answer 2

I was just pointed to this solution:

import java.lang.reflect.ParameterizedType;  public abstract class A<B> {     public Class<B> g() throws Exception {         ParameterizedType superclass =             (ParameterizedType) getClass().getGenericSuperclass();          return (Class<B>) superclass.getActualTypeArguments()[0];     } } 

This works if A is given a concrete type by a subclass:

new A<String>() {}.g() // this will work  class B extends A<String> {} new B().g() // this will work  class C<T> extends A<T> {} new C<String>().g() // this will NOT work