strange problem in an array

Question

I'm working on a little server app with Java. So, I'm getting informations from different client, and if information comes in, the following method is called:

public void writeToArray(String data) {
    data = trim(data);
    String[] netInput = new String[5];
    netInput[0]="a";
    netInput[1]="a";
    netInput[2]="a";
    netInput[3]="a";
    netInput[4]="a";
    netInput = split(data, ",");
    pos_arr = PApplet.parseInt(netInput[0]);
    rohr_value = PApplet.parseInt(netInput[1]); // THIS LINE KICKS OUT THE ERROR.
    if(pos_arr >0 && pos_arr<100) {
        fernrohre[pos_arr] = rohr_value;
        println("pos arr length: " + fernrohre[pos_arr]);
        println("pos arr: " + pos_arr);
    }

The console on OS X gives me the following error:

Exception in thread "Animation Thread"
java.lang.ArrayIndexOutOfBoundsException:1
 at server_app.writeToArray(server_app.java:108) at server_app.draw(server_app.java:97)
 at processing.core.PApplet.handleDraw(PApplet.java:1606)
 at processing.core.PApplet.run(PApplet.java:1503)
 at java.lang.Thread.run(Thread.java:637)

As you can see, I tried to fill the array netInput with at least 5 entries, so there can't be an ArrayIndexOutOfBoundsException.

I don't understand that, and I'm thankful for your help!

It would work already for me, if I can catch the error and keep the app continuing.

Please provide the code of the split method

user85421
– user85421

2010-10-01 11:05:47 +00:00
Commented Oct 1, 2010 at 11:05 — user85421
– user85421, Commented Oct 1, 2010 at 11:05
@Carlos I read that as data.split(","); good observation.

Qwerky
– Qwerky

2010-10-01 13:01:12 +00:00
Commented Oct 1, 2010 at 13:01 — Qwerky
– Qwerky, Commented Oct 1, 2010 at 13:01

Qwerky · Accepted Answer · 2010-10-01 10:09:34Z

10

You put 5 Strings into the array, but then undo all your good work with this line;

netInput = split(data, ",");

data obviously doesn't have any commas in it.

answered Oct 1, 2010 at 10:09

Qwerky

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2 Comments

Manoj Govindan Over a year ago

+1 to What @carlos said. Almost all of us here assumed that split works as expected.

Mikko Wilkman Over a year ago

I think the fundamental misunderstanding here is the array re-initialization even if the problem itself exists in the split-method or not. The way that the array is incorrectly "pre-initialized" with five strings really to me points out that it's not expected for the split to return enough values.

Roman · Accepted Answer · 2010-10-01 10:11:16Z

2

In this line

netInput = split(data, ",");

your array is being reinitialized. Your split method probably returns an array with only 1 element (I can guess that data string doesn't contain any ",").

answered Oct 1, 2010 at 10:11

Roman

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Comments

Community · Accepted Answer · 2017-05-23 12:18:38Z

2

Update

The split() method is custom, not String.split. It too needs to be checked to see what is going wrong. Thanks @Carlos for pointing it out.

Original Answer

Consider this line:

netInput = split(data, ",");

This will split the data string using comma as a separator. It will return an array of (number of commas + 1) resulting elements. If your string has no commas, you'll get a single element array.

Apparently your input string doesn't have any commas. This will result in a single element array (first element aka index = 0 will be the string itself). Consequently when you try to index the 2nd element (index = 1) it raises an exception.

edited May 23, 2017 at 12:18

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answered Oct 1, 2010 at 10:10

Manoj Govindan

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4 Comments

nbuechi Over a year ago

Yes, I understand this, but I send: c.write(FERNROHR_ID + "," +target +"\n"); So data has a "," in it. I want the first part, BEFORE the comma is netInput[0], and the second part, AFTER the comma is in netInput[1]. Can someone help me with that?

Manoj Govindan Over a year ago

@nbuechi: you need to double check the data. Try printing it to sysout and see what turns up. You logic for splitting is correct, but apparently the data is not showing up in the way want.

user85421 Over a year ago

please note that the code is NOT (directly) calling String.split()!

Manoj Govindan Over a year ago

@Carlos: Thanks dude. That was a good catch. I've updated my answer accordingly.

DeliveryNinja · Accepted Answer · 2010-10-01 10:14:50Z

1

You need some defensive code,

if(netInput.length > 1)
   pos_arr = PApplet.parseInt(netInput[0]);
   rohr_value = PApplet.parseInt(netInput[1]);

answered Oct 1, 2010 at 10:14

DeliveryNinja

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1 Comment

nbuechi Over a year ago

thanks a lot, maybe this is already enough, because it's working for an uncertain time, and maybe one time, he doesn't get the comma, and then it crashes. thanks.

Andriy Sholokh · Accepted Answer · 2010-10-01 10:10:18Z

1

You make netInput = split(data, ","); and
split(data, ",");

returns one element array

answered Oct 1, 2010 at 10:10

Andriy Sholokh

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3 Comments

nbuechi Over a year ago

What I do, when I send is: c.write(FERNROHR_ID + "," +target +"\n"); So data has a "," in it. I want the first part, BEFORE the comma is netInput[0], and the second part, AFTER the comma is in netInput[1]. Can someone help me with that?

Andriy Sholokh Over a year ago

then I can assume that FERNROHR_ID - is an empty string.

Andriy Sholokh Over a year ago

Or target is an empty string

Koekiebox · Accepted Answer · 2010-10-01 10:55:09Z

1

You are re-assigning your netInput variable when the split() method is called.

The new value might not have an array count of 5.

Can you provide the source for the split() method?

edited Oct 1, 2010 at 10:55

answered Oct 1, 2010 at 10:11

Koekiebox

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1 Comment

Koekiebox Over a year ago

I assume the split() method is part of the class/super-class where the writeToArray() method is called. Since String is final and cannot be extended.

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