Why do I keep getting java.lang.reflect.InvocationTargetException

Question

I keep getting java.lang.reflect.InvocationTargetException whenever I run my code

package test;

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.chart.LineChart;
import javafx.scene.chart.NumberAxis;
import javafx.scene.chart.XYChart;
import javafx.stage.Stage;
 
public class Test extends Application {
    
    private static int[] xarray;
    private static int[] yarray;
    
  public static void main(String[] args) {
    countgradient(3, 1, 1) ;
    launch(args);
    System.out.println(xarray[0]);
    }
          
  public static int[] countgradient( int cx, int cy, int con ){
      int x1 = 1;
      int y1 = (cx*x1+con)/cy ;
      System.out.println(y1);
      int x2 = 2;
      int y2 = (cx*x2+con)/cy ;
      System.out.println(y2);
      int gradient = (y2-y1)/(x2-x1);
      System.out.println("The gradient is " + gradient);
      xarray[0] = x1;
      xarray[1] = x2;
      yarray[0] = y1;
      yarray[1] = y2;
      return xarray;
  }
 
  @Override
  public void start(Stage stage) {
        stage.setTitle("Line Chart Sample");
        //defining the axes
        final NumberAxis xAxis = new NumberAxis();
        final NumberAxis yAxis = new NumberAxis();
        //creating the chart
        final LineChart<Number,Number> lineChart = 
                new LineChart<>(xAxis,yAxis);
        //defining a series
        XYChart.Series series = new XYChart.Series();
        series.setName("Line");
        //populating the series with data
        series.getData().add(new XYChart.Data(xarray[0], yarray[0]));
        series.getData().add(new XYChart.Data(xarray[1], yarray[1]));
        
        Scene scene  = new Scene(lineChart,800,600);
        lineChart.getData().add(series);
       
        stage.setScene(scene);
        stage.show();
    }
}

and I dont really understand the reasons for why I keep getting this problem

The full result that I get is

4
7
The gradient is 3
java.lang.reflect.InvocationTargetException
    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 com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
    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 sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.NullPointerException
    at test.Test.countgradient(Test.java:30)
    at test.Test.main(Test.java:16)
    ... 11 more
Exception running application test.Test
C:\Users\Owner\AppData\Local\NetBeans\Cache\8.2\executor-snippets\run.xml:53: Java returned: 1
BUILD FAILED (total time: 3 seconds)

Is it caused by using the array to run the chart or is it something else, should I use a different way to define the array

The null pointer exception at the bottom is the relevant part. You're assigning to an array which is `null`. You need to allocate your array — Silvio Mayolo, Jun 08 '21 at 18:02
It's caused by a NullPointerException on line 30 of `Test.java`, in the `countgradient` method. I suspect it's because `xarray` is null - what do you expect to initialize that array? — Jon Skeet, Jun 08 '21 at 18:02

Why do I keep getting java.lang.reflect.InvocationTargetException

0 Answers0