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

Determining the Class of a Generic Type in Java

In Java, when dealing with generic classes, it's often necessary to determine the specific type that a generic type holds at runtime. However, generic type information is erased during compilation, making it a challenge to access it directly.

Let's consider an example:

public class MyGenericClass<T> {

  public void doSomething() {
    T instance = (T) thirdPartyLib.create(T.class);
  }
}

In this scenario, T.class will result in an Illegal class literal error because the generic type T is unknown. To address this, a workaround is required.

Workaround Solution

One effective workaround is to pass the type as a parameter to a static method, which will provide the class information to the generic class. Here's an example:

public class MyGenericClass<T> {

  private final Class<T> type;

  public static <U> MyGenericClass<U> createWithClass(Class<U> type) {
    return new MyGenericClass<>(type);
  }

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

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

This method allows you to pass the class type explicitly, ensuring that the generic class has access to the necessary information. While this workaround may not be the most elegant solution, it provides a reliable way to determine the class of a generic type at runtime.

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