Java interface using JPype

[odedtgr]

Hi,
Im looking for a good example or explanation of how to implement a Java interface, that is, I would like to provide a Java app an interface to methods in a python app. Read the documentation, but i think it assumes a deeper Java knowledge than i have.
Thanks

[Thrameos]

Use JImplements and JOverride. https://jpype.readthedocs.io/en/latest/api.html#decorators Java: public interface MyInterface { void doSomething(int i); } Python: @jpype.JImplements(MyInterface) class MyImplemention(object): @jpype.JOverride def doSomething(self, i): print(i) There is nothing more to it.

[odedtgr]

Hi Karl, Sorry to trouble you, but I'm still having trouble. Perhaps you could help me with this example:

1. I have a Java app with a window and a button that calls a method testMethod.
2. I also have a Python app with a window and a button that generates a random number.
   When both apps are running, once I click the button on the Java App, I would like the Python generate_random method to be called and return the number to Java.
   Hope this is not too much.
   Thanks, Oded  

--------------Java App------------- 
import javax.swing.;
import java.awt.;

public class testWindow extends JFrame {// implements TestInterface {
   
    private JButton button;

    public testWindow() {
        // Set window properties
        setTitle("Simple Window");
        setSize(300, 200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
       
        // Create button
        button = new JButton("Test Button");
        button.addActionListener(e -> testMethod());
       
        // Add button to center of window
        setLayout(new FlowLayout(FlowLayout.CENTER));
        add(button);
    }

    public void testMethod() {
         System.out.println("Test method called from button click");
     }
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            testWindow window = new testWindow();
            window.setVisible(true);
        });
    }
}

--------------Python App------------
import tkinter as tk
import random

def generate_random():
    random_num = random.randint(1, 100)
    result_label.config(text=f"Random Number: {random_num}")
return random_num

root = tk.Tk()
root.title("Random Number Generator")
root.geometry("300x200")

button = tk.Button(root, text="Generate Random Number", command=generate_random)
button.pack(pady=20)

result_label = tk.Label(root, text="Click button to generate")
result_label.pack(pady=20)

root.mainloop()

[Thrameos]

I am not sure exactly how one would run both a Java and Tk in the same python application. I wouldn't use the pattern. Generally I write a GUI in Java first then have Python launch it.

I will have to assume that your awt application actually works (I use JavaFX not awt)

import javax.swing.;
import java.awt.;

public class TestWindow extends JFrame {// implements TestInterface {

    public DoubleSupplier call;
   
    private JButton button;

    public testWindow() {
        // Set window properties
        setTitle("Simple Window");
        setSize(300, 200);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
       
        // Create button
        button = new JButton("Test Button");
        button.addActionListener(e -> testMethod());
       
        // Add button to center of window
        setLayout(new FlowLayout(FlowLayout.CENTER));
        add(button);
    }

    public void testMethod() {
         double v = call.getAsDouble();
         System.out.println("Test method called from button click "+ v);
     }
    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            TestWindow window = new TestWindow();
            window.setVisible(true);
        });
    }
}

--------------Python App------------
import random

import jpype
import jpype.imports

jpype.startJVM(classpath="blah blah")

from mypkg import TestWindow
from javax.swing import SwingUtilities

window = TestWindow()

def generate_random():
    random_num = random.randint(1, 100)
    result_label.config(text=f"Random Number: {random_num}")
    return random_num

# We can pass a Python function to a Java functor and connect functionality between languages.
window.call = generate_random

def mylaunch():
  window.setVisible()

# We pass a function in as a runnable and Java will run it in the GUI thread
SwingUtilities.invokeLater(mylaunch)

#There is a little special code required if running on a OSX machine as we are required to ensure the main loop gets serviced,
# But otherwise stuff just runs.

[odedtgr]

Wow, that was quick. My use case is different: I have an industrial tool with a main controller (Windows computer) that runs a Java application to manage the tool. From time to time the tool requires calibration. The Java has a scheduler to handle that. I would like to write the calibration as a python app that the Java scheduler can invoke (shell script to run compiled python) and the java needs to be able to control the python app. not just by passing arguments on startup, but by calling python methods. I was thinking of creating an interface to python methods that the Java will be able to call. Again, appreciate you time and effort Oded

…

On Mon, Feb 10, 2025 at 5:55 PM Karl Nelson ***@***.***> wrote: I am not sure exactly how one would run both a Java and Tk in the same python application. I wouldn't use the pattern. Generally I write a GUI in Java first then have Python launch it. I will have to assume that your awt application actually works (I use JavaFX not awt) import javax.swing.; import java.awt.; public class TestWindow extends JFrame {// implements TestInterface { public DoubleSupplier call; private JButton button; public testWindow() { // Set window properties setTitle("Simple Window"); setSize(300, 200); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setLocationRelativeTo(null); // Create button button = new JButton("Test Button"); button.addActionListener(e -> testMethod()); // Add button to center of window setLayout(new FlowLayout(FlowLayout.CENTER)); add(button); } public void testMethod() { double v = call.getAsDouble(); System.out.println("Test method called from button click "+ v); } public static void main(String[] args) { SwingUtilities.invokeLater(() -> { TestWindow window = new TestWindow(); window.setVisible(true); }); } } --------------Python App------------ import random import jpype import jpype.imports jpype.startJVM(classpath="blah blah") from mypkg import TestWindow from javax.swing import SwingUtilities window = TestWindow() def generate_random(): random_num = random.randint(1, 100) result_label.config(text=f"Random Number: {random_num}") return random_num # We can pass a Python function to a Java functor and connect functionality between languages. window.call = generate_random def mylaunch(): window.setVisible() # We pass a function in as a runnable and Java will run it in the GUI thread SwingUtilities.invokeLater(mylaunch) #There is a little special code required if running on a OSX machine as we are required to ensure the main loop gets serviced, # But otherwise stuff just runs. — Reply to this email directly, view it on GitHub <#1260 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AFM2Z3VQYBYA6NQOE7XJCDD2PDDWJAVCNFSM6AAAAABWZH75J6VHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTEMJSGI2DINA> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[Thrameos]

You can push as much as you want through functors or implementation of interfaces. I have exposed large Python sections to Java for my GUI work. Just decide if you need to make it class like (requiring bridge classes for each object) or if it is more functional in which case you just copy all the Python methods to corresponding functors in Java. Both methods can work. Unfortunately, I never found enough users for the reverse bridge which automatically writes the bridge classes for Java. With that you could do things like run matplotlib and numpy from Java side. It was very cool, but required a full test bench and a lot of user review. The manual method is more cumbersome, but it works well enough for most applications. Good luck.