http://googlecloudplatform.github.io/google-cloud-java/0.11.0/index.html has a code snippet:

DatastoreOptions options = DatastoreOptions.newBuilder()
  .setProjectId(PROJECT_ID)
  .setAuthCredentials(AuthCredentials.createForJson(
    new FileInputStream(PATH_TO_JSON_KEY))).build();

However, setAuthCredentials isn't a method on DatastoreOptions.Builder- it's setCredentials: http://googlecloudplatform.github.io/google-cloud-java/0.11.0/apidocs/com/google/cloud/datastore/DatastoreOptions.Builder.html. It also has it taking an AuthCredentials object- GoogleCredentials is probably the correct substitute here.