Generic class that accepts either of two types

Question

I want to make a generic class of this form:

class MyGenericClass {}

Problem is, I want to be acceptable for T to b

Answer 1

The answer is no. At least there is no way to do it using generic types. I would recommend a combination of generics and factory methods to do what you want.

class MyGenericClass {
  public static MyGenericClass newInstance(Long value) {
    return new MyGenericClass(value);
  }

  public static MyGenericClass newInstance(Integer value) {
    return new MyGenericClass(value);
  }

  // hide constructor so you have to use factory methods
  private MyGenericClass(T value) {
    // implement the constructor
  }
  // ... implement the class
  public void frob(T number) {
    // do something with T
  }
}

This ensures that only MyGenericClass and MyGenericClass instances can be created. Though you can still declare an variable of type MyGenericClass it will just have to be null.