Shows how to embed Jython and use it as a code generator to create dynamic classes with runtime-defined behavior. Circa 2002.

PythonEmbeddedExample.java

import org.python.util.PythonInterpreter;
import org.python.core.*;

public class PythonEmbeddedExample {
    private static final String EOL = "\n";
    private static final PythonInterpreter INTERP = new PythonInterpreter();
    private static final String I = "\t";

    public static void main(String[] args) throws PyException {
        exchangeObjects();
        swing();
        dynamicImplementations();
        calc();
    }

    private static void calc() {
        System.out.println(INTERP.eval("(5+2j)/(-4+12.3j)"));
        Object[] arr = (Object[])INTERP.eval("('fafla', 'mafla', 3, 3.14, 3.14-1j)").__tojava__(Object[].class);
        for (int i = 0; i < arr.length; i++) {
            Object o = arr[i];
            System.out.println("o:"+o.getClass()+" = " + o);
        }
    }

    private static void dynamicImplementations() {
        TestInterface testInstance = createDynamicImplementation("This is a parameter string");
        System.out.println(testInstance.test());
    }

    private static TestInterface createDynamicImplementation(String retval) {
        // define the class
        INTERP.exec("import TestInterface" + EOL
                + "class TestImpl(TestInterface):" + EOL
                +  " def test(self):" + EOL
                +  "  return \"" + retval + "\""
        );

        // instantiate the class
        INTERP.exec("testInstance = TestImpl()");

        // get instance
        return (TestInterface) INTERP.get("testInstance", TestInterface.class);
    }

    private static void swing() {
        INTERP.exec("from pawt import swing" + EOL
                + "import java" + EOL
                + "def exit(e): java.lang.System.exit(0)" + EOL
                + "frame = swing.JFrame('Swing Example', visible = 1)" + EOL
                + "button = swing.JButton('Close Me!', actionPerformed = exit)" + EOL
                + "frame.contentPane.add(button)" + EOL
                + "frame.pack()"
        );
    }

    private static void exchangeObjects() {

        System.out.println("Hello, java");

        INTERP.exec("import sys" + EOL + "print sys");

        INTERP.set("a", new PyInteger(42));

        INTERP.exec("print a");
        INTERP.exec("x = 2+2");
        PyObject x = INTERP.get("x");

        System.out.println("x: " + x);
        System.out.println("Goodbye, cruel world");
    }
}

TestInterface.java

public interface TestInterface {
    String test();
}