An annotation that indicates the version number since a member or a type has been present. This annotation is useful to manage versioning of your JSON classes for a web-service.

This annotation has no effect unless you build com.google.gson.Gson with a GsonBuilder and invoke the GsonBuilder#setVersion(double) method.

Here is an example of how this annotation is meant to be used:

public class User {
  private String firstName;
  private String lastName;
  @Since(1.0) private String emailAddress;
  @Since(1.0) private String password;
  @Since(1.1) private Address address;
}

If you created Gson with new Gson(), the toJson() and fromJson() methods will use all the fields for serialization and deserialization. However, if you created Gson with Gson gson = new GsonBuilder().setVersion(1.0).create() then the toJson() and fromJson() methods of Gson will exclude the address field since it's version number is set to 1.1.