Databases
StackOverflow2013
Postsdbo
POImpossible IndexOutOfBound happening on ArrayList.get(). Any clue?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POImpossible IndexOutOfBound happening on ArrayList.get(). Any clue?
    primarykey
    data
    text
    <p>I've got a very strange error, that would like to share with you.</p> <p>I've the following code (simplified):</p> <pre><code>public ArrayList&lt;String&gt; al = new ArrayList&lt;String&gt;(); public void doSomething() { int size = al.size(); for(int i=0; i&lt;size; i++) { if (al.get(i) != null) { System.out.println(al.get(i)); String sPath = al.get(i); File fFile = new File(sPath); fFile.delete(); // Simplified. It has some error checking } } } </code></pre> <p>I have one error, saw in the production environment:</p> <pre><code>java.lang.IndexOutOfBoundsException: Index: 1, Size: 0 at java.util.ArrayList.RangeCheck(Unknown Source) at java.util.ArrayList.get(Unknown Source) at MYCLASS.soSomething(MICLASS.java:1944) [...] </code></pre> <p>Line 1944 is <code>if (al.get(i) != null) {</code>.</p> <p>What! How can it raise IndexOutOfBound?!</p> <p>The problem is that the error does not reproduce. I've been able to raise it only once in the dev environment, but trying to reproduce it was not possible (it dit not raise again)... so no way to look for a pattern in the error.</p> <p>So my only option is simple: read the code and use the brain.</p> <p>So I browse the code of <code>java.util.ArrayList.get()</code>:</p> <pre><code>public class ArrayList&lt;E&gt; [...]{ public E get(int index) { RangeCheck(index); return (E) elementData[index]; } private void RangeCheck(int index) { if (index &gt;= size) throw new IndexOutOfBoundsException("Index: "+index+", Size: "+size); } } </code></pre> <p>So it throws the exception because <code>index &gt;= size</code>... How is it possible? The <code>for()</code> sweeps from <code>0</code> to <code>size-1</code>... It is impossible! It cannot raise the error!</p> <p>Wait a second! This code is not thread-safe. Maybe another thread is calling <code>clear()</code> or <code>remove*()</code> on the ArrayList... Studying the code, it is not possible. So I run it, set a breakpoint on line 1944 and watch the threads in that moment, and effectively, the other running threads have nothing to do with this issue.</p> <p>Any other clue?</p> <p>Kernnigan &amp; Pike: "Debugging [...]Something impossible occurred, and the only solid information is that it really did occur."</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USJavier Sedano
    1. USJavier Sedano
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POImpossible IndexOutOfBound happening on ArrayList.get(). Any clue?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COI suspect the bug is in "// It actually does some more things". Please post more code - *ideally* a short but complete program. For example: do you ever modify the array list within that loop? Do you ever modify `i` within the loop?
      singulars
      1. POImpossible IndexOutOfBound happening on ArrayList.get(). Any clue?
      1. USJon Skeet
    2. COAre you sure that there really is no other thread messing with the list? If the code you have shown is complete, that looks like the only explanation. Or you "simplified" the code sample too much.
      singulars
      1. POImpossible IndexOutOfBound happening on ArrayList.get(). Any clue?
      1. USThilo
    3. COThis is really a test to see if we can read minds and figure out what goes here `// It actually does some more things`. I vote this question for the most questionable question of the day award. To be believed.
      singulars
      1. POImpossible IndexOutOfBound happening on ArrayList.get(). Any clue?
      1. USHovercraft Full Of Eels
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload