How to solve "Exception in thread "main" java.lang.NullPointerException" -

this question has answer here:

• what nullpointerexception, , how fix it? 12 answers

i'm supposed instantiate object passing double array containing values , invoke methods , results should come out on console. code:

public class client {      public static void main(string[] args) {         rainlog log = new rainlog(1.0,2.0,3.0,4.0,5.0,6.0,7.0,8.0,9.0,10.0);         double[] inrangevalues = log.getinrange(0,0);         for(int i=0; i<inrangevalues.length; i++)         system.out.println(inrangevalues[i]);   } } 

after running appears on console:

exception in thread "main" java.lang.nullpointerexception @ comp125.rainlog.getinrange(rainlog.java:73) @ comp125.client.main(client.java:7) 

i click on:

at comp125.rainlog.getinrange(rainlog.java:73) 

it directs me loop:

for(int i=0; i<data.length; i++) 

which passed junit test not sure why. new java , programming not sure problem at.

data null @ line 73 of rainlog.java.

there must somethiing wrong junit test if passed without detecting bug.