Question

I have a snippet code for instantiation of a generic type as following:

public class GenericMessageMapper<I ,X>
{
   public X xFromI(I imf)
   {
      // do thing by imf argument
      Class<X> clazz = (Class<X>)((ParameterizedType)
                                   this.getClass()
                                       .getGenericSuperclass())
                                       .getActualTypeArguments()[1];
      X x = clazz.newInstance(); 
   }
}

Above code worked fine but MyEclipse show a warning on the code(a yellow under line on preparing clazz variable line) by this message :Type safety: Unchecked cast from Type to Class<X>

I temporary add following annotation in above of xFromI method:

@SuppressWarnings("unchecked")

What is reason of this warning and what is solution?

Answer 1

ftom2 is right – in usual situation you should perform instance check (instanceof) before cast in case of this warning. But in your case this is impossible because generics in Java was implemented by erasure. Class<X> is not reified type so it is impossible to use it for instance check and only way to turn off the warning is to use @SuppressWarnings(value = "unchecked").
To learn more about generics you can use this book.