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The Java Specialists' Newsletter
Issue 1862010-07-30
Category:
Language
Java version: Java 6 Iterator Quizby Olivier CroisierAbstract:
Most of the northern hemisphere is on holiday, so here is a quick quiz for those poor souls left behind manning the email desk. How can we prevent a ConcurrentModificationException in the iterator?
Welcome to the 186th issue of The Java(tm) Specialists' Newsletter, sent from the
beautiful island of Crete. Yesterday morning, Olivier
Croisier sent me a quiz that kept me wondering for a
while. Olivier teaches our Java Specialist Master Course
in France (in French). Since most of my readers are on
holiday, I thought a small quiz would be great for those
poor souls left behind manning the help desk.
Iterator Quiz by Olivier Croisier
Hi everyone,
Here is my Java Quiz #40, I hope you'll like it - if you're
not somewhere on a beach drinking Mojitos :)
The idea behind this quiz was found during the last Java Specialist training
session, when we were musing through the
JDK source code. One of the students, Romain Revol, helped
me prove it worked.
As it is summer (despites the dark clouds and low temperature in Paris),
I tried to tell a short, funny (I hope) story to explain what you are
expected to do in this quizz.
So, without further ado, here it is !
To please your Project Manager, a former developer (yeaaars ago), you
sometimes let him help you develop some "very important" parts of your
application.
Today, he's in charge of displaying "Hello World" by iterating on a list
containing those words. Alas, distracted by his going on vacation this
very afternoon, he forgets to add "World" to the list before starting
the iteration. Trying to correct his mistake, he adds it a few lines
later, but now his code unexpectedly breaks down at runtime ("this must
be a JVM bug !").
A few minutes before leaving, he asks you to find a solution in his
absence, with the following instructions :
Do not modify his existing code, it's Perfect (of course).
The FIXME tag shows where you're allowed to insert your corrective code
He must be able to understand your solution when he comes back (so using Reflection is not an option).
Are you worth the trust of your beloved Manager ?
final List<String> list = new ArrayList() {{ add("Hello"); }};
final Iterator<String> iterator = list.iterator();
System.out.println(iterator.next());
list.add("World");
// FIXME : work here while I'm sunbathing
System.out.println(iterator.next());
Have fun !
Olivier
Once you've figured it out, please head over to Olivier's blog
The Coders Breakfast.net to see if you got it right.
Heinz
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