Question

I was looking into the Guava library and I came across an empty anonymous inner class in TypeToken.

TypeToken<List<String>> stringListTok = new TypeToken<List<String>>() {};

What is exactly use of empty anonymous inner class and what are the useful scenarios where it can be helpful?

Answer 1

The purpose of this is to allow TypeToken to find the superclass of the instance – which will preserve the type argument information.

For example, although an ArrayList<String> object doesn’t know that that its element type is String, due to erasure, the superclass information is not lost, so new ArrayList<String>{} knows that its superclass is ArrayList<String>, not just ArrayList. TypeToken uses that technique to represent a constructed generic type.