Keep getting java.lang.NullPointerException when trying to read from JSON file

Question

I'm trying to read from a json file in order to create visual images via processing. My code so far is:

public void generateShape(JSONObject file) {
    //convert file to json object
    JSONArray shapes = (JSONArray) file.get("shapes");
    for (Object o : shapes) {
        JSONObject json_shape = (JSONObject)o;
        //getting shape id and function so we know which shapes to create
        id = ((Number) json_shape.get("id")).intValue();
        func = ((Number) json_shape.get("func")).intValue();
        animate = ((Number) json_shape.get("animate")).intValue();
        stroke_weight = ((Number) json_shape.get("stroke_weight")).floatValue();

        JSONArray strokes = (JSONArray) json_shape.get("stroke");
        Iterator<Float> iterator = strokes.iterator();
        index = 0;
        while(iterator.hasNext())
        {
            stroke[index] = ((Number)iterator.next()).floatValue();
            index++;

        }

stoke[] is an array of floats which will control the colour of the stroke. The json file im parsing from is

{
   "shapes": [
{
  "id":0,
  "func":1,
  "stroke":[143,50,200],
  "stroke_weight": 70,
  "animate": 1,
  "jelly_func": 5,
  "points":[268,330,400,333,74,210,90,300]

  }

  ]
}

im getting the error at the line:

     stroke[index] = ((Number)iterator.next()).floatValue();

I'm using the json.simple library and all solutions i've seen are for org.json library

I could hard code the values in the stroke array but I wanted to try iteration instead. Any tips/guidance?

full stack trace is

java.lang.NullPointerException
at ImageLoader.generateShape(ImageLoader.java:35)
at Sketch.setup(Sketch.java:48)
at processing.core.PApplet.handleDraw(PApplet.java:2404)
at processing.awt.PSurfaceAWT$12.callDraw(PSurfaceAWT.java:1557)
at processing.core.PSurfaceNone$AnimationThread.run(PSurfaceNone.java:313)

where sketch is:

 ImageLoader image = new ImageLoader();
    JSONParser parser = new JSONParser();
    try {
        JSONObject file = (JSONObject) parser.parse((new FileReader("save_data.json")));
        image.generateShape(file);

    }
    catch (FileNotFoundException e)
    {
        e.printStackTrace();
    }
    catch (Exception e)
    {
        e.printStackTrace();
    }

eta: ok so upon removing the line causing the exception, and checking if my json values are even being read I can confirm the values being parsed are correct when I print them to console. I just now need to put them in an array

does your file only have that 1 shape in there? if there are more than one shape can you print out the id then post that shape's json ? — Charles, Oct 19 '18 at 15:57
did you initialize your stroke anywhere? `float[] stroke = new float[strokes.size()];` — Charles, Oct 19 '18 at 16:10
Use your debugger, or add System.out.println() traces in the code, to know what is null at that line. It can by stroke, or the value returned by iterator.next(). Act accordingly. — JB Nizet, Oct 19 '18 at 16:15
We can't really help you if we can't see a [mcve]. Also please try to [debug your code](https://happycoding.io/tutorials/processing/debugging) to understand exactly what's going on. — Kevin Workman, Oct 19 '18 at 16:22

score 0 · Answer 1 · answered Oct 19 '18 at 16:22

I still think you didn't initialize the array right... can you try this code and see if it works?

public void generateShape(JSONObject file) {
    // convert file to json object
    JSONArray shapes = (JSONArray) file.get("shapes");
    for (Object o : shapes) {
        JSONObject json_shape = (JSONObject) o;
        // getting shape id and function so we know which shapes to create
        int id = ((Number) json_shape.get("id")).intValue();
        int func = ((Number) json_shape.get("func")).intValue();
        int animate = ((Number) json_shape.get("animate")).intValue();
        float stroke_weight = ((Number) json_shape.get("stroke_weight")).floatValue();

        JSONArray strokes = (JSONArray) json_shape.get("stroke");
        Iterator<Float> iterator = strokes.iterator();
        int index = 0;
        float[] stroke = new float[strokes.size()];
        while (iterator.hasNext()) {
            stroke[index] = ((Number) iterator.next()).floatValue();
            index++;

        }
    }
}

Keep getting java.lang.NullPointerException when trying to read from JSON file

1 Answers1