Java ArrayList java.lang.NullPointerException

Question

I'm sorry I am very new to programming and have encountered what I hope is a simple problem to solve. I'll put my code in here and explain what I am trying to do below.

public class main {

static ArrayList<Interpreter> ints1;
static ArrayList<Customer> custs1;
static MainFunctions mainF;

static { //Static blocks execute first - and are great for initializing data!
    ArrayListPopulator ALP1 = new ArrayListPopulator();
    ints1 = ALP1.populateALints1(); // error occurs on this method call.
    custs1 = ALP1.populateALcusts1();
    mainF = new MainFunctions(ints1, custs1);
}

public static void main(String[] args) {

    mainF.findNearestInterp("Frank");
}

}

ArrayList Populator:

import java.util.ArrayList;
public class ArrayListPopulator {

private ArrayList<Interpreter> ints1ToGo;
private ArrayList<Customer> custs1ToGo;

public ArrayList<Interpreter> populateALints1() {
    //Format is "String pName, int pAge, String PGender,
            // int pSignLevel, boolean pDeafBlindExp, double pLatitude, double pLongitude, String pTown"

            //Gender must be "Male"||"Female"

            //In future this could be done by scanning a local config text file. Wish that I knew that stuff :l

    Interpreter Elliott = new Interpreter("Elliott", 23, "Male", 6, true, 52.098049, 0.277860, "Linton");
    ints1ToGo.add(Elliott); //error occurs here.

    Interpreter Sarah = new Interpreter("Sarah", 20, "Female", 3, true, 52.209950, 0.137774, "Cambridge");
    ints1ToGo.add(Sarah);

    Interpreter Argibarge = new Interpreter("Argibarge", 42, "Male", 3, false, 52.599199, -0.264226, "Peterborough");
    ints1ToGo.add(Argibarge);

    Interpreter Bruce = new Interpreter("Bruce", 30, "Male", 2, false, 50.717527, -3.540192, "Exeter");
    ints1ToGo.add(Bruce);

    Interpreter Medusa = new Interpreter("Medusa", 1009, "Female", 4, false, 55.867795, -4.267566, "Glasgow");
    ints1ToGo.add(Medusa);

    return ints1ToGo;
}

public ArrayList<Customer> populateALcusts1() {
    //Format is "String pName, int pAge, String PGender,
    //boolean pDeafBlind, double pLatitude, double pLongitude, String pTown"

    //Gender must be "Male"||"Female"

    //In future this could be done by scanning a local config text file. Wish that I knew that stuff :l

    Customer Frank = new Customer("Frank", 30, "Male", false, 56.113482, -3.934635, "Stirling");
    custs1ToGo.add(Frank);

    Customer Eleanor = new Customer("Eleanor", 23, "Female", true, 52.622439, 1.281124, "Norwich");
    custs1ToGo.add(Eleanor);

    Customer Pacha = new Customer("Pacha", 43, "Male", false, 52.397273, -0.727392, "Kettering");
    custs1ToGo.add(Pacha);

    Customer Roy = new Customer("Roy", 69, "Male", false, 51.746940, -1.257345, "Oxford");
    custs1ToGo.add(Roy);

    Customer Jenette = new Customer("Jenette", 16, "Male", false, 51.871877, 0.357845, "Great Dunmow");
    custs1ToGo.add(Jenette);
    return custs1ToGo;
}

}

Error Message at runtime:

Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.NullPointerException
at ArrayListPopulator.populateALints1(ArrayListPopulator.java:16)
at main.<clinit>(main.java:23)

The thing I am most new to in this code is the static {} block to initialize my main ArrayLists of data from the data stored in the ArrayListPopulator class. It would appear that I am not initializing the ArrayList properly, or adding the elements properly, or I'm not assigning the reference variable properly.

Thank you so much for any help!

"Static blocks execute first - and are great for initializing data" and are great for causing difficulties with unit testing, mocking, controlling initialisation order between modules etc. Use with care. I would much prefer initialisation in a constructor — Brian Agnew
– Brian Agnew, Commented Apr 16, 2014 at 15:36
line 16 refers to a function taking a customers name and comparing it to the database of interpreters and their distance from the customer - however it is not yet implemented. — TristonianDP
– TristonianDP, Commented Apr 16, 2014 at 15:43
Thank you very much for being so helpful in answering my first question here :) I hope one day to be able to share some knowledge in return! — TristonianDP
– TristonianDP, Commented Apr 16, 2014 at 15:47

Konstantin Yovkov · Accepted Answer · 2014-04-16 15:32:09Z

8

The ints1ToGo list is not initialized.

Either do it in the constructor:

public ArrayListPopulator() {
    ints1ToGo = new ArrayList<Interpreter>();
}

or before you try to add elements.

ints1ToGo = new ArrayList<Interpreter>();
Interpreter Elliott = new Interpreter("Elliott", 23, "Male", 6, true, 52.098049, 0.277860, "Linton");
ints1ToGo.add(Elliott); //error won't occur here anymore.

Note that you will have to do the same for the custs1ToGo list, because (as I can see) you're not initializing it anywhere and it's used in the populateALcusts1 method.

answered Apr 16, 2014 at 15:32

Konstantin Yovkov

63k9 gold badges107 silver badges152 bronze badges

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

Comments

Mohsen Kamrani · Accepted Answer · 2014-04-16 15:34:04Z

0

You never initialize ints1ToGo:

ints1ToGo = new ArrayList<Interpreter>();

answered Apr 16, 2014 at 15:34

Mohsen Kamrani

7,4975 gold badges48 silver badges73 bronze badges

Comments

Kalle Richter · Accepted Answer · 2014-04-16 15:34:35Z

0

ints1ToGo is never initialized. Change private ArrayList<Interpreter> ints1ToGo; to private ArrayList<Interpreter> ints1ToGo = new ArrayList<Interpreter>();

answered Apr 16, 2014 at 15:34

Kalle Richter

8,85429 gold badges96 silver badges209 bronze badges

Comments

Farzad · Accepted Answer · 2014-04-16 15:36:07Z

0

You will need to initialize both array instances

private ArrayList<Interpreter> ints1ToGo = new ArrayList<Interperter>();
private ArrayList<Customer> custs1ToGo = new ArrayList<Customer>();

answered Apr 16, 2014 at 15:36

Farzad

1,14210 silver badges21 bronze badges

Collectives™ on Stack Overflow

Java ArrayList java.lang.NullPointerException

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related