Java: Array Index Out of Bounds

Question

I get this exception:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 100
at Vindu.<init>(setevelger.java:64)
at setevelger.main(setevelger.java:22)

when I'm running this code:

    public knapp seter[]=new knapp[100]; //knapp means button

    int rad=0; //rows
    int sete=0; //seats     
    int antallSeter=0; //number of seats
    for (int i=0;i<10;i++){
        for (int j=0;j<10;j++){
            seter[antallSeter]= new knapp("Rad "+(rad+1)+", Sete "+(sete+1));
            seter[antallSeter].setBackground(Color.GREEN);

            add(seter[antallSeter]); 
            antallSeter++;              
            if(j==10){
                sete=0;
                }else{              
                    sete++; 
                    }           
            }
        rad++;
        }   

    //creates an eventlistener
    Knappelytter lytteren = new Knappelytter();
    seter[antallSeter].addActionListener(lytteren);
    pack();

and if I do this:

public knapp seter[]=new knapp[120]; //knapp means button

I get this error:

Exception in thread "main" java.lang.NullPointerException
at Vindu.<init>(setevelger.java:64)
at setevelger.main(setevelger.java:22)

both errors come at runtime when the window is being created.

So, the code is supposed to create 100 buttons and store them in an array, and each button is to have a row and seat number.

I'm stuck, I have no idea where to look anymore..

Should I perhaps use an arraylist?

This isn't really answering your question, but it'll help. you have if(j==10) in your loop that states ..;j<10;.. which means that j will never equal 10. Also, unless they're used outside of your loops sete and rad are not needed, you can just use i and j. "rad " +(i+1)+", Sete "+(j+1)); Then you don't need the parts after antallSeter++; — Shaded
– Shaded, Commented Feb 6, 2012 at 21:31
could you show us what's on setevelger.java line 64 and 22 ? — bernabas
– bernabas, Commented Feb 6, 2012 at 21:32
Pleas don't start your class name with a lower case (new knapp(...)). This does not fit the java naming convention and it prevents confusion. ;) — Sebastian Stiehl
– Sebastian Stiehl, Commented Feb 6, 2012 at 21:42

user1190541 · Accepted Answer · 2012-02-06 21:28:41Z

2

In your for cycles antalSetter is increased to 100 in last cycle - first exception, if you increase array length to 120 - you are accesing element at index 100 that is null.

answered Feb 6, 2012 at 21:28

user1190541

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3 Comments

user1190541 Over a year ago

why you test for j == 10 ? some micro - optimalization :) ?

TM89 Over a year ago

Im testing because I want each seat to have a seat number, and each row is supposed to have 10 seats, so when j==10 so that next row starts from 0 again:)

user1190541 Over a year ago

you testing is included in for cycle condition evaluation phase (int j=0;j<10;j++) - there is no way how j == 10 , do not need sete variable, use j instead

Ted Hopp · Accepted Answer · 2012-02-06 21:30:33Z

1

In your code, you have this reset code:

if (j==10) {
    sete=0;
} else {
    sete++;
}

However, it can never be that j == 10, so sete never gets reset to 0. I don't know if that's what's causing the exception, but it's definitely a problem with your code. The condition should probably be if (j==9) { ...

answered Feb 6, 2012 at 21:30

Ted Hopp

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Comments

calebds · Accepted Answer · 2012-02-06 21:36:09Z

1

Both exceptions occur because the penultimate line:

seter[antallSeter].addActionListener(lytteren);

is outside of the double for loop, where antallSeter will have been incremented beyond the number of existing (1^st exception) or populated (2^nd exception) indices of seter.

If I understand correctly, and you'd like to add an event listener to every button, you could change to:

// ..

    if(j == 10) {
        sete=0;
    } else {              
        sete++; 
    }

    seter[antallSeter].addActionListener(new Knappelytter());

}
rad++;
// etc ..

edited Feb 6, 2012 at 21:36

answered Feb 6, 2012 at 21:27

calebds

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MByD · Accepted Answer · 2012-02-06 21:27:14Z

0

After the last loop, the value of antallSeter is 100. which is an index out of bounds in the line:

seter[antallSeter].addActionListener(lytteren);

You should probably move the lines:

Knappelytter lytteren = new Knappelytter();
seter[antallSeter].addActionListener(lytteren);

Inside the outer loop.

answered Feb 6, 2012 at 21:27

MByD

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Arvind Chavhan · Accepted Answer · 2015-09-25 06:02:29Z

0

Initialise seter with 101 size.

public knapp seter[]=new knapp[101];

answered Sep 25, 2015 at 6:02

Arvind Chavhan

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1 Comment

André Schild Over a year ago

A array with 100 buttons won't need a size of 101 elements

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