i am more familiar with Python than with Java and after writing some java code i still think Python code is much faster to write, although Python runs much slower than Java. and for a beginner, the oppotunity to type in functions or change states when the program is running, then see the effects immediately (this is so called "interactive mode", as oppose to modify code -> compile -> test run) is a great help.
Jython is Python which runs on Java Virtual Machine, and it is possibly compatible with any Java libraries, so a JPCT game could be written mostly in Python code, although some parts should be written in Java or even C language to keep a high running performance.

now let's see how a JPCT program can be written with Jython.

to start up the program, create a shortcut such as start.bat.
-i means interactive mode, pause to let yourself read any error messages.
@c:\jythonpath\jython.exe -Djava.library.path=jar_path -i mygame.py
@pause

minimal example of a JPCT program, save as mygame.py
import sys,time; sys.path+=['jar_path','jar_path/jpct.jar','jar_path/lwjgl.jar','jar_path/lwjgl_util.jar']
from com.threed.jpct import *; from com.threed.jpct.util import *; from org.lwjgl.opengl import Display

fb=FrameBuffer(640,480,FrameBuffer.SAMPLINGMODE_NORMAL)
running=1
timeToSleep=0.01 # 0.01 second

def sleepSomeTime(): time.sleep(timeToSleep) # or calculate a value to make framerate constant

def GameLogic(): return
def pollKeyboard(): return

def mainLoop():
    global running
    while running:
        GameLogic(); fb.clear(); fb.update(); sleepSomeTime(); fb.display(); pollKeyboard()
        # if some key event: running=0
        if Display.isCloseRequested(): Display.destroy(); break

mainLoop()
if "some key event" happens and interactive mode is used, mainLoop stops and you can type in commands, such as change timeToSleep to 0.02, then call mainLoop again after changing running back to 1. this is an example of the benefit of interactive mode.

to import your own java class, put class files in jar_path or append another path to sys.path, then import YourJavaClass

if you know both Python language and Java, you may find this approach has some advantages.

can i achieve multipass rendering of the same world (with different camera settings) or sequential rendering of multiple worlds in a specified order?

reproject2d3dws returns a direction vector, not a position in world space. project3d2d requires a position in world space as input.

i like to write something like:
import org.lwjgl.opengl;
class { method() { opengl.Display.setTitle("abc"); } }
but no matter what i tried:
import org.lwjgl;
import org.lwjgl.opengl.*
...
jave doens't compile.
do i have to write { org.lwjgl.opengl.Display.method(); } every time?

i tried adding the Canvas to Frame, also disabled software renderer, but still a new GL window showed up, i thought GL should render into the Canvas which was added into Frame.
i use Frame because i don't know how to manipulate the window created by FrameBuffer, for example change the style, size, position. and fullscreen mode is not good during development so i always prefer windowed mode. and java doesn't expose HWND so i can't even use DLL calls to change the window.
could you tell me how to create an opengl window without border and sized 1280x766? in pseudo code?

i found out i need to add this in .classpath file <classpathentry kind="lib" path="xxx/xxx.jar"/>

it can be imported now.

developing on the device is slower but i can do it anywhere anytime, kind of fun.