java error message null pointer exception

Question

This is the error i received when i tried running my code below. my teacher said we could ask anywhere for help. I would be very grateful if someone could help me with this error

java.lang.NullPointerException
    at Practise_Assessment.main(Practise_Assessment.java:35)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:272)

here is my code if it is needed

import java.text.NumberFormat;
import java.util.Arrays;

public class Practise_Assessment {

    public static String absences(String prompt) {// user input for name and
    // days absent
        System.out.println(prompt);
        java.util.Scanner keyboard = new java.util.Scanner(System.in);
        return keyboard.nextLine();
    }


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

        int numDayEntries ;
        int numNameEntries;
        int[] daysArray = null ;
        String[] nameArray = null ;

        boolean done = false;

        while (!done) {
            System.out.println("enter # to stop");
            String absences = absences("enter name of person absent then the amount of days they were absent");// the value of the users input

            for(numDayEntries =0; numDayEntries < daysArray.length;numDayEntries++ ){
                daysArray = new int[numDayEntries];
            }
            for(numNameEntries = 0; numNameEntries < nameArray.length;numNameEntries++ ){

                nameArray = new String[numNameEntries];    
            }

            if (absences.equalsIgnoreCase("#")) {
                done = true;    
            } else {
                String DaysAbsent =absences.replaceAll("[^0-9]", "") ;
                int daysAbsent = ((Number) NumberFormat.getInstance().parse(DaysAbsent)).intValue();//   converts a string to an int
                String absentee = absences.replaceAll("\\d", "");// replace all digits in the user input to nothing leaving just the name

                daysArray[numDayEntries] = daysAbsent; 
                nameArray[numNameEntries] = absentee;
            }
        } 
        System.out.println(Arrays.toString(daysArray));
    }
}

thanks everyone who replied, you guys(and girls) helped so much — user3023714
– user3023714, Commented Apr 1, 2014 at 7:17
@user3023714 then, you should accept the answer which helped you to solve it. — Keerthivasan
– Keerthivasan, Commented Apr 1, 2014 at 7:39

chrylis -cautiouslyoptimistic- · Accepted Answer · 2014-04-01 05:34:50Z

2

Your for loop is counting to daysArray.length, but daysArray is null. Furthermore, your for loops don't make any sense anyway; you're creating and then throwing away lots of identical arrays. It's very unclear what your code is trying to accomplish, since you're asking for a single person's name and then a single number indicating the number of absences.

The recommended approach is to (1) use an object that contains both the student's name and the number of absences, keeping this information together in a single record and (2) use a List instead of an array if you don't know how many items you're going to need, since a List is of variable size.

answered Apr 1, 2014 at 5:34

chrylis -cautiouslyoptimistic-

77.5k21 gold badges127 silver badges167 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Keerthivasan · Accepted Answer · 2014-04-01 05:34:43Z

1

daysArray is null and .length is accessed from null reference. That's the cause of NPE.You need to initialize array before it is being used. Your for loop is not making any sense at all.

answered Apr 1, 2014 at 5:34

Keerthivasan

12.9k2 gold badges34 silver badges55 bronze badges

Comments

Jason · Accepted Answer · 2014-04-01 05:35:15Z

1

The stack trace is telling you that the problem is on line 35 of the Practise_Assessment class. You need to look at that line.

If line 35 is this:

for(numDayEntries =0; numDayEntries < daysArray.length;numDayEntries++ ){

then it is probably because you did not initialise daysArray - you set it to null.

answered Apr 1, 2014 at 5:35

Jason

11.8k3 gold badges45 silver badges48 bronze badges

Comments

Karthigeyan Vellasamy · Accepted Answer · 2014-04-01 05:35:52Z

1

daysArray is null numNameEntries IS NULL

answered Apr 1, 2014 at 5:35

Karthigeyan Vellasamy

2,0667 gold badges33 silver badges51 bronze badges

Comments

Birlla · Accepted Answer · 2014-04-01 05:41:17Z

1

Issues in your for loop. Your arrays are set to NULL.

Initialize your array before going to use.

Then try it , you'll get what you want.

answered Apr 1, 2014 at 5:41

Birlla

1,8502 gold badges16 silver badges18 bronze badges

Comments

Erran Morad · Accepted Answer · 2014-04-01 05:42:23Z

1

This line is the cause of the exception - for(numDayEntries =0; numDayEntries < daysArray.length;numDayEntries++ ).

Look at the exception you got - NULL-PointerException or NPE. It tells us that some REFERENCE or TYPE has been set as NULL, that is, we did not assign an appropriate object to it. Eg. Car nfs = null;. We should have done Car nfs = new Car();

Now, the only OBJECT in the error causing line is daysArray. Everything else is an int. So, you should see the rest of your code if daysArray is being assigned an object properly or not. Maybe you forgot or maybe the it happens due to a logical error.

Long winded way, but I did it since you are new.

answered Apr 1, 2014 at 5:42

Erran Morad

4,78312 gold badges45 silver badges77 bronze badges

Collectives™ on Stack Overflow

java error message null pointer exception

6 Answers 6

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related