How to Determine the Class of a Generic Type in Java?

Determining the Class of a Generic Type: Exploring Alternatives

In the realm of generic programming, it often becomes crucial to determine the specific class of the generic type currently in use. However, Java's generic type erasure mechanism poses a challenge to this endeavor.

To address this issue, let's delve into an example that mimics a real-world scenario:

public class MyGenericClass<T> {
  public void doSomething() {
    // Imagine a 3rd party library call that expects a Class object
    T bean = (T) someObject.create(T.class);
  }
}

Unfortunately, the above code will fail with an "Illegal class literal for the type parameter T" error. This is because generic type information is erased at runtime, rendering the direct use of T.class impossible.

So, how can we overcome this obstacle? A workaround emerged as a viable solution: introducing a static factory method that accepts the desired class as a parameter.

public class MyGenericClass<T> {

  private final Class<T> clazz;

  public static <U> MyGenericClass<U> createMyGeneric(Class<U> clazz) {
    return new MyGenericClass<>(clazz);
  }

  private MyGenericClass(Class<T> clazz) {
    this.clazz = clazz;
  }

  public void doSomething() {
    T instance = clazz.newInstance();
  }
}

This approach allows you to explicitly specify the generic class during object creation, effectively bypassing the runtime erasure issue. However, it does come with a drawback: it adds some boilerplate code and slightly complicates the API. Nevertheless, it remains an effective workaround when the determination of the class type is indispensable.

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