Question

What is the best way to retrieve the runtime value of a generic parameter for a generic class? For example:

public class MyClass<T> {

  public void printT() {
    // print the class of T, something like:
    // System.out.println(T.class.getName());
  }

}

So if I call

new MyClass<String>().printT() 

it will print “String”

Answer 1

You don’t. Due to type erasure that information is (mostly) lost at runtime. If you really need the class this is what you do:

public class MyClass<T> {
  private final Class<T> clazz;

  public MyClass(Class<T> c) {
    if (c == null) {
      throw new NullPointerException("class cannot be null");
    }
    clazz = c;
  }

  public void printT() {
    System.out.println(clazz.getName());
  }
}

and then you have access to it.