Member Avatar for echellwig

Hi,

I am trying to interface between Java and Python in a program called Eclipse. Any insight on how to do this would be helpful. Thanks!

Elise

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  • Latest Post Latest Post by jcao219

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As asked, the first decision is what "interface" means here: does Java need to call Python, does Python need to call Java, must the integration be in-process (same JVM) or can it be out-of-process, and are CPython C-extensions (numpy, scipy, etc.) required? Answering those questions narrows the right tool quickly.

As suggested, Jython is the simplest when an in-JVM, in-process Python runtime is acceptable and the code is pure Python (no C extensions). It lets Java and Python objects interoperate directly and is easy to add to an Eclipse Java project. Caveat: Jython historically lacked CPython C-extension support and Python-3 parity, so it is not a fit if the project depends on native Python modules.

If CPython compatibility or native extensions are required, consider:

  • JEP (embed a real CPython interpreter inside the JVM) — good for calling Python (with C-extensions) from Java.
  • JPype or Py4J — common ways to call Java libraries from Python (JPype is JNI-based and often faster; Py4J uses a gateway socket and is easy to set up).
  • Running Python as an external process and using STDIO, sockets, HTTP/REST or gRPC — simple, language-agnostic, and isolates runtimes.
  • GraalVM polyglot — an alternative for polyglot apps if adopting Graal is acceptable.

A minimal Java pattern for running an external Python script (avoid deadlocks by consuming streams):

Process p = new ProcessBuilder("python", "script.py", "arg1")
    .redirectErrorStream(true)
    .start();
BufferedReader r = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line;
while ((line = r.readLine()) != null) System.out.println(line);
p.waitFor();

Quick troubleshooting checklist:

  • If embedding, ensure matching architectures (32 vs 64-bit) and compatible JVM/Python versions.
  • For external processes, use absolute interpreter paths or set PATH in Eclipse run configs.
  • Always consume stdout and stderr or redirect errors to avoid blocking.
  • In Eclipse, PyDev helps manage Python interpreters and Jython integration; add bridging JARs to the project classpath for JVM-side solutions.

Recommended Answers

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Member Avatar for HarryPad

OK, I think you could share a little more information.

Now what is it that you are trying to accomplish? (in English).

And what is it that your are trying to interface?

Do you want to call python from Java (if so - why?)

Do you want to call Java from python (if so - why?)

And have you looked at (ie: google for it) Jython - a python implemented in java that has hooks so that it can be called from Java?

Anyway - we are all glad to help here but you really do need to share more information so that we can steer you in the best way.

Harry

Member Avatar for jcao219

Definitely Jython. It's Python that is implemented on the Java platform.
Look into it at http://www.jython.org/.

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