get instantiated type variable in java

Question

I would like to check if the instantiated type of a generic class has certain properties, eg:

class Foo<T> {
  void bar () { 
    if (T instanceof Serializable)   // does not compile
      ...
  } 
}

I am wondering if the generic information is totally lost during runtime? And does that mean there is no way to accomplish what I would like to do?

Answer 1

And does that mean there is no way to accomplish what I would like to do?

You can write:

class Foo<T> {
  private final Class<T> clazz;

  Foo (final Class<T> clazz) { // require creator to supply a Class<T>
    this.clazz = clazz;
    if (clazz == null) {
      throw new NullPointerException();
    }
  }

  void bar () { 
    if (Serializable.class.isAssignableFrom(clazz)) {
      ...
    }
  } 
}

Answer 2

You are right, generic type information is lost at run-time. It's called Type Erasure .Compiler would remove all the generic type and do the cast's(if necessary) at run time. and all the