Starting and killing the JVM

API

jt.javabridge.JARS

a list of strings; gives the full path to some JAR files that should be added to the class path in order for all the features of the jtypes.javabridge to work properly.

Environment

In order to use the jtypes.javabridge in a thread, you need to attach to the JVM’s environment in that thread. In order for the garbage collector to be able to collect thread-local variables, it is also necessary to detach from the environment before the thread ends.

Without GUI (headless mode)

Using the JVM in headless mode is straighforward:

import os
from jt import javabridge

javabridge.start_vm(run_headless=True)
try:
    print(javabridge.run_script('java.lang.String.format("Hello, %s!", greetee);',
                                dict(greetee='world')))
finally:
    javabridge.kill_vm()

With GUI on the Java side

Using the JVM with a graphical user interface is much more involved because you have to run an event loop on the Python side. You also have to make sure that everything executes in the proper thread; in particular, all GUI operations have to run in the main thread on Mac OS X. Here is an example, using a wxPython app to provide the event loop:

import os
import wx
from jt import javabridge

javabridge.start_vm()

class EmptyApp(wx.App):
    def OnInit(self):
        javabridge.activate_awt()
        return True

try:

    app = EmptyApp(False)

    # Must exist (perhaps the app needs to have a top-level window?), but
    # does not have to be shown.
    frame = wx.Frame(None)

    javabridge.execute_runnable_in_main_thread(javabridge.run_script("""
        new java.lang.Runnable() {
            run: function() {
                with(JavaImporter(java.awt.Frame)) Frame().setVisible(true);
            }
        };"""))

    app.MainLoop()

finally:

    javabridge.kill_vm()

With GUI on both the Java side and the Python side

Finally, an example combining AWT for GUI on the Java side with wxPython for GUI on the Python side:

import os
import wx
from jt import javabridge

class EmptyApp(wx.PySimpleApp):
    def OnInit(self):
        javabridge.activate_awt()

        return True

javabridge.start_vm()

try:
    app = EmptyApp(False)

    frame = wx.Frame(None)
    frame.Sizer = wx.BoxSizer(wx.HORIZONTAL)
    launch_button = wx.Button(frame, label="Launch AWT frame")
    frame.Sizer.Add(launch_button, 1, wx.ALIGN_CENTER_HORIZONTAL)

    def fn_launch_frame(event):
        javabridge.execute_runnable_in_main_thread(javabridge.run_script("""
            new java.lang.Runnable() {
                run: function() {
                    with(JavaImporter(java.awt.Frame)) Frame().setVisible(true);
                }
            };"""))
    launch_button.Bind(wx.EVT_BUTTON, fn_launch_frame)

    frame.Layout()
    frame.Show()
    app.MainLoop()

finally:

    javabridge.kill_vm()