When constructing a generic object, can you pass its type from a variable?

Question

If I have a generic class like this:

class SomeClass<T> { 
  public aFunction(T anArg) {
    // some implementation
  }
}

Is there then a way to instantiate the SomeClass, using a variable of the Class type?

I basically want to be able to do this:

Class var = String.class; // just an example, obviously
SomeClass<?> anInstance = new SomeClass< var >();

Or is there a workaround?

No. What good do you think that would do? – Sotirios Delimanolis Dec 24 '14 at 13:29 — Sotirios Delimanolis, Dec 24 '14 at 13:29
Seems to be a duplicate indeed. Thanks Paul. – Erik Dec 24 '14 at 13:38 — Erik, Dec 24 '14 at 13:38

score 1 · Answer 1 · answered Dec 24 '14 at 13:40

1

Java uses type erasure, so at runtime generic types are not aware of their type parameters. So the simple answer is "no".

Depending on your needs, you could either use one of the Class.newInstance methods, or keep the class object in a field.

answered Dec 24 '14 at 13:40

Michael Bar-Sinai

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score 1 · Answer 2 · answered Dec 24 '14 at 13:59

From a purely syntactic point of view, no, you can't. Type arguments must be type names (or the wildcard, ?) known at compile time. They cannot be variables or other expressions that evaluate to a value.

It is still unclear why you need this, especially since your anInstance is of type SomeClass<?>, in which case you wouldn't care about the type argument used.

When constructing a generic object, can you pass its type from a variable?

2 Answers2