Hi, I’m a bit confused by the question, but Camunda has a robust REST API which is documented here https://docs.camunda.org/manual/latest/reference/rest/. The APIs that you referenced are also included.
Camunda also has an internal “Java API” that can be accessed using java code in a java delegate for example, and documentation can be found here https://docs.camunda.org/javadoc/camunda-bpm-platform/7.13/.
If this is not what you’re looking for, can you please elaborate on your question.