public <U> ExtendedConverter<S,T,U> join(DynamoDBTypeConverter<T,U> target) {
            return AbstractConverter.<S,T,U>join(this, target);
        }
An abstract converter with additional general purpose functions.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/datamodeling/DynamoDBTypeConverter.java