Why is this getting NullPointerException & ArrayIndexOutOfBoundsException errors

Question

Getting a NullPointerError on line 24 (second for loop) and an arrayoutofindexexception on the main method. I have no idea how to solve this and an explanation would be much appreciated. Please help!

Edit: 'NullPointerError' solved, just needed to initialize the ArrayList for it, but still can't work out the 'ArrayOutOfIndexException' error.

import java.util.*;

public class SnackBar
{
    private Random randomizer;
    private String[] flavours;
    private SnackMachine barMachine;
    ArrayList<Student> students;

    public SnackBar(int numStudents, int packetsBarMachine, int costPacket)
    {
        randomizer = new Random();
        flavours = new String[] {"prawn cocktail", "tango cheese", "natural", "paprika", "salt and vinegar"};
        barMachine = new SnackMachine(packetsBarMachine, costPacket);
 students = new ArrayList<Student>();

        for(int i = 0; i < packetsBarMachine; i++)
        {
            barMachine.addPack(new PackOfCrisps(randomFlavour()));
            i++;
        }

        for(int j = 0; j < numStudents; j++)
        {
            students.add(new Student(randomFlavour(), barMachine));            
            j++;
        }
    }

    public String randomFlavour()
    {
        int random = randomizer.nextInt(flavours.length);
        return flavours[random];
    }

    public void describe()
    {
        System.out.println("The SnackBar has " + students.size() + " hungry students.");
        System.out.println("The Snackmachine has:");
        System.out.println(barMachine.countPacks("prawn cocktail") + " packets of prawn cocktail crisps,");
        System.out.println(barMachine.countPacks("tango cheese") + " packets of tango cheese crisps,");
        System.out.println(barMachine.countPacks("natural") + " packets of natural crisps,");
        System.out.println(barMachine.countPacks("paprika") + " packets of paprika crisps,");
        System.out.println(barMachine.countPacks("salt and vinegar") + " packets of salt and vinegar crisps.");
    }

    public void runSnackBar(int nSteps)
    {
        int step = 1;

        while(step <= nSteps)
        {
            System.out.println("Time Step " + step);
            describe();
            int atRandom = randomizer.nextInt(students.size());
            students.get(atRandom).snackTime();
            step++;
        }
    }

    public static void main(String[] args)
    {
        SnackBar bar = new SnackBar (Integer.parseInt(args[4]), Integer.parseInt(args[20]), Integer.parseInt(args[5]));

        bar.runSnackBar(Integer.parseInt(args[30]));
    }
}

Do you have realy 20 arguments for your program? – Jens Dec 11 '14 at 09:04 — Jens, Dec 11 '14 at 09:04

Eran · Accepted Answer · 2014-12-11T09:10:18.483

0

First thing, you should initialize the ArrayList<Student> students list.

Integer.parseInt(args[30]) is also suspicious, since for that not to throw an exception, you have to supply 31 command line arguments. Same goes for all your other attempts to access elements of args array without checking its length first.

edited Dec 11 '14 at 09:10

answered Dec 11 '14 at 09:03

Eran

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Ah yes, silly mistake there. Still getting the Arrayindexoutofbound error on the main method, however... – ASCH Dec 11 '14 at 09:08
@ASCH did you see my edit? – Eran Dec 11 '14 at 09:09
Just saw it, thanks for pointing it out. How would you propose I go about it? – ASCH Dec 11 '14 at 09:13
@ASCH always make sure `args.length > i` before accessing `args[i]` – Eran Dec 11 '14 at 09:15
Nvm, another silly mistake on my part. I needed to simply enter an integer instead of an arg. Thanks a lot for the help! – ASCH Dec 11 '14 at 09:21

Why is this getting NullPointerException & ArrayIndexOutOfBoundsException errors

1 Answers1