为什么我在 Processing.py 中遇到 strokeWeight() 的 NullPointerException？

Question

A quick disclaimer: I'm a bit of a newbie, so this issue might be just me not seeing the obvious, but basically when I run

def setup():
    size(400,400)

def test():
    strokeWeight(5)
    circle(100, 100, 100)

test()

in Processing I get the following error:

processing.app.SketchException: java.lang.NullPointerException
at processing.core.PApplet.strokeWeight(PApplet.java:14431)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.python.core.PyReflectedFunction.__call__(PyReflectedFunction.java:188)
    at org.python.core.PyReflectedFunction.__call__(PyReflectedFunction.java:206)
    at org.python.core.PyObject.__call__(PyObject.java:497)
    at org.python.core.PyObject.__call__(PyObject.java:501)
    at org.python.core.PyMethod.__call__(PyMethod.java:141)
    at org.python.pycode._pyx58.test$2(sketch_210426a.pyde:6)
    at org.python.pycode._pyx58.call_function(sketch_210426a.pyde)
    at org.python.core.PyTableCode.call(PyTableCode.java:171)
    at org.python.core.PyBaseCode.call(PyBaseCode.java:139)
    at org.python.core.PyFunction.__call__(PyFunction.java:413)
    at org.python.pycode._pyx58.f$0(sketch_210426a.pyde:1)
    at org.python.pycode._pyx58.call_function(sketch_210426a.pyde)
    at org.python.core.PyTableCode.call(PyTableCode.java:171)
    at org.python.core.PyCode.call(PyCode.java:18)
    at org.python.core.Py.runCode(Py.java:1614)
    at org.python.core.Py.exec(Py.java:1658)
    at org.python.pycode._pyx57.f$0(/var/folders/vf/3zy00t252_372n6n1n060tc00000gn/T/sketch_210426a6112183873956099370/sketch_210426a.pyde:96)
    at org.python.pycode._pyx57.call_function(/var/folders/vf/3zy00t252_372n6n1n060tc00000gn/T/sketch_210426a6112183873956099370/sketch_210426a.pyde)
    at org.python.core.PyTableCode.call(PyTableCode.java:171)
    at org.python.core.PyCode.call(PyCode.java:18)
    at org.python.core.Py.runCode(Py.java:1614)
    at org.python.core.Py.exec(Py.java:1658)
    at org.python.util.PythonInterpreter.exec(PythonInterpreter.java:276)
    at jycessing.PAppletJythonDriver.processSketch(Unknown Source)
    at jycessing.PAppletJythonDriver.findSketchMethods(Unknown Source)
    at jycessing.Runner.runSketchBlocking(Unknown Source)
    at jycessing.mode.run.SketchRunner.lambda$startSketch$3(Unknown Source)
    at java.lang.Thread.run(Thread.java:748)

    at jycessing.mode.run.SketchRunner.convertPythonSketchError(Unknown Source)
    at jycessing.mode.run.SketchRunner.lambda$startSketch$3(Unknown Source)
    at java.lang.Thread.run(Thread.java:748)

Interestingly enough, I am only returned the error when any one of Processing's built in functions (such as setup() , draw() or mouseClicked ) is defined as well, so if I ran:

def why_arent_you_working():
    print("please")
    
def test():
    strokeWeight(5)
    circle(100, 100, 100)
    
test()
why_arent_you_working()

it would work for some reason.

I've tried 10 diffrent threads concerning NullPointerException but I just can't seem to find what I did wrong. As I've prefaced this post, I am a newbie, so its probably some stupid oversight of mine but it would be great if someone helped me out.

Answer 1

When you declare a variable what you're doing is creating something that points towards that variable. Ie when we create a variable x = 5. x is just a reference that points towards the number 5 .

NullPointerException occurs when you're pointing at something that is Null . I'm not all too familiar with the strokeWeight method so I can't tell you exactly but I can try to help more if you add a tiny bit more code for me.

In the log files (The second part you've coded in) you can click the line number and it will take you to which part of a method the error is coming from.

So below it tells us that the NullPointerException is coming from somewhere called processing.core.PApplet.strokeWeight in line 14431. If you could click the number and copy the method into your original post I can try help a little more from there.

processing.app.SketchException: java.lang.NullPointerException at processing.core.PApplet.strokeWeight(PApplet.java:14431)

Answer 2

This might be a result of "mixing active and static modes". Active mode is when you use setup() and/or draw() , and static mode is when you don't. Basically, if you're using setup() , you can't call any functions outside of an indentation (or a variable definition). The standard way to draw a circle on the screen is like this:

def setup():
    size(400,400)

def draw():
    strokeWeight(5)
    circle(100, 100, 100)

draw() is called just like setup() is: it's automatically called without you explicitly calling it anywhere.

Keep in mind that draw() is a loop, so it will run continuously until noLoop() is called.