Thread: Driver error, null pointer exception when creating an instance of a class?

Okay so I have no idea why this is happening. Its not even a question about methodology I am just wondering if I should build a new project or something at this point because I can't see how/why I am getting an error. Here is my code:

Driver:

package graphalgorithms;
 
import java.io.*;
import java.util.*;
 
public class GraphAlgorithms {
 
    public static void main(String[] args) throws IOException {
 
        PrimsAlgorithm graph = new PrimsAlgorithm();
 
        String inputFile = "src/input/input.txt";
        String fName = inputFile;
        String thisLine;
        String[][] data = new String[100][100];
        int count = 0;
        int size = 0;
 
        FileInputStream geek = new FileInputStream(fName);
        BufferedReader in = new BufferedReader(new InputStreamReader(geek, "UTF-16"));
 
        while ((thisLine = in.readLine()) != null) {
 
            String[] array = thisLine.split(",");
            System.arraycopy(array, 0, data[count], 0, array.length);
            size = array.length;
            count++;
        }
 
        String[] vert = new String[size];
        System.arraycopy(data[0], 0, vert, 0, size);
 
        String[][] arrayData = new String[size][size];
        for (int i = 0; i < size; i++) {
            System.arraycopy(data[i + 1], 0, arrayData[i], 0, size);
        }
 
        Scanner sc = new Scanner(System.in);
        System.out.println("Please select the algorithm you wish to run: "
                + "1 for Prim's algorithm, 2 for Kruskal's algorithm"
                + "or 3 for Floyd-Warshall’s algorithm ");
 
        while (sc.hasNext()) {
 
            int i = sc.nextInt();
            switch (i) {
 
                case 1:
 
                    System.out.println("You chose Prim's algorithm.");
                    graph.initializeData(arrayData,vert);
                    break;
 
                case 2:
                    System.out.println("You chose Kruskal's algorithm.");
                    break;
 
                case 3:
                    System.out.println("You chose Floyd-Warshall's algorithm.");
                    break;
 
                default:
                    System.out.println("Invalid entry");
                    break;
            }
            System.out.println();
            System.out.println("Please select the algorithm you wish to run: "
                    + "1 for Prim's algorithm, 2 for Kruskal's algorithm"
                    + "or 3 for Floyd-Warshall’s algorithm ");
        }
    }
}

Class:

package graphalgorithms;
 
public class PrimsAlgorithm {
 
    private String[] verticies;
    private int[][] actualData;
    private final int max = Integer.MAX_VALUE;
    private final int V = verticies.length;
 
    public void initializeData(String[][] incomingArray, String [] incomingVerticies) {
 
        verticies = incomingVerticies;
 
        actualData = new int[incomingArray.length-1][incomingArray.length];
 
        for(int i = 0; i < actualData.length; i++){
            for(int j = 0; j < incomingArray.length; j++){
 
                if (incomingArray[i][j].equals("\u221E")) {
 
                    actualData[i][j] = 999999;      //if inf symbol is seen replace with high value weight
                } else {
                    actualData[i][j] = Integer.parseInt(incomingArray[i][j]);
                }
            }
        }
 
        //primsMST(actualData);
    }
}

Now when I run the program it errors at line 10 where I create an instance of class PrimsAlgorithm even though I have ran the program successfully before. I am not sure when this stared happening as a change a few names around but not much then all of a sudden...

This is the error its giving me:

run:
Exception in thread "main" java.lang.NullPointerException
at graphalgorithms.PrimsAlgorithm.<init>(PrimsAlgorit hm.java:8)
at graphalgorithms.GraphAlgorithms.main(GraphAlgorith ms.java:10)
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)

Any ideas? This is line 10:

PrimsAlgorithm graph = new PrimsAlgorithm();

Originally Posted by Norm

What variable was null when line 8 was executed?
Look at line 8 and find the variable with the null value.

So its odd because there is no variable in line 8. Line 8 is the method deceleration:

public static void main(String[] args) throws IOException {

--- Update ---

Yeah I can't seem to figure out why this isn't working. I tried creating a new project but got the same error.

Wow, okay I am sorry. I guess I just missed that. Thank you!