Null pointer exception when trying to use getResourceAsStream() function

Question

I am relatively new to Java, and as a learning experience, tried to build a classifier in java by reading a dataset from a file called "dataset.csv"

This is the code I wrote for the whole class:

import java.io.IOException;
import weka.classifiers.trees.J48;
import weka.classifiers.Classifier;
import weka.classifiers.Evaluation;
import weka.core.converters.CSVLoader;
import weka.core.Instances;

public class classifier {
    public static final String DATASET = "dataset.csv";
    
    public static Instances getData(String filename) throws IOException
    {
        CSVLoader loader = new CSVLoader();
        loader.setSource(classifier.class.getResourceAsStream("/"+filename));
        System.out.println("getData function running");
        Instances dataset = loader.getDataSet();
        
        return dataset;
    }
    
    public static void J48Classifier() throws Exception
    {
        
        Instances dataset = getData(DATASET);
        Classifier j48 = new J48();
        
        j48.buildClassifier(dataset);
        
        Evaluation eval = new Evaluation(dataset);
        eval.evaluateModel(j48,dataset);
        
        System.out.println("Evaluation with dataset: ");
        System.out.println(eval.toSummaryString());
        
        System.out.println("Expression as per the algorithm: ");
        System.out.println(j48);
        
        System.out.println(eval.toMatrixString());
        System.out.println(eval.toClassDetailsString());    
    }
    
    public static void main(String args[]) throws Exception
    {
        J48Classifier();
    }
}

But once I run the code, I am getting this error:

This is my file Structure for reference (the dataset.csv file is located in the src directory of the below cited image):

Can anyone help me figure out if I have missed out on something?

I would also move the data file into a path off of where the java/class files are located. Please check out the answers in the duplicate questions. — Hovercraft Full Of Eels, Oct 24 '21 at 19:56
Do you mean I create a new directory and then get my file from there instead? — Purohit Iyer, Oct 24 '21 at 19:59
While @fracpete means well with his suggestion, I strongly urge you not to follow it as your program will fail completely if/when you decide to create a jar or if you try to run it on another computer. — Hovercraft Full Of Eels, Oct 24 '21 at 21:38
The argument to `getResourceAsStream` is not a file path. If you want to open a file, use `Files.newInputStream` or `new FileInputStream`. If you want to open a resource, that resource must be a path inside your application. — VGR, Oct 24 '21 at 22:56
Personally, I wouldn't package datasets inside jars, but provide them via command line arguments to the class that you're executing. — fracpete, Oct 25 '21 at 01:42

Null pointer exception when trying to use getResourceAsStream() function

0 Answers0