如何在Junit for NeticaJ中解决NullPointerException？

Question

//This is my Main Class here when i call methodTwo in this class i got numnodes=4 but when i tried to access methodTwo in testclass i got NullPointerException.

package Netica;

import norsys.netica.Environ;
import norsys.netica.Net;
import norsys.netica.NodeList;
import norsys.netica.Streamer;

import org.junit.runner.JUnitCore;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;

import NeticaTestCases.HNetTest;

public class HNet {
    private static long startTime = System.currentTimeMillis();
    private static Net net;
    private static NodeList nodes;
    int numNodes;

    public int methodOne() {
        System.out.println("we are in first methodOne");
        return 1;
    }

    public int methodTwo() {
        numNodes = nodes.size();
        System.out.println("we are in 2nd methodTwo");
        return numNodes;
    }

    public static void main(String[] args) {
        try {


            // Read in the net file and get list of all nodes and also Total
            // number of nodes:
            net = new Net(neStreamer("DataFiles/KSA_4_Nodes_noisySum.dne"));
            nodes = net.getNodes();

            HNet temp = new HNet();
            temp.methodOne();
            System.out.println("numNodes========>"+temp.methodTwo());//get 4

        } catch (Exception e) {
        }

    }
}

//this is my testclass

package NeticaTestCases;

import static org.junit.Assert.assertEquals;
import org.junit.Before;
import org.junit.Test;
import static org.junit.Assert.fail;

import Netica.HNet;

public class HNetTest {
    HNet temp;

    @Before
    public void setUp() {
        temp = new HNet ();
    }

    @Test
    public void CheckNumNodes() {
        temp.methodOne();
        System.out.println("numNodes========>"+temp.methodTwo());       
        }   

}

please help me out how to resolve NullPointerException in junit testcases.

Answer 1

Adding a statement initialising the nodes should get you rid of the exception -

@Before
public void setUp() {
    temp = new HNet ();
    temp.nodes = new NodeList();
} 

Also, would suggest you to try and improve on few points -

1. Debug the difference between your main method and CheckNumNodes() test method.
2. Use of getters and setters