Play My Code: Wacky Cannon

I have always wanted to make a projectile game and now I have! I've just published Wacky Cannon on Play My Code. The aim of the game is to control the cannon using your mouse and click to shoot the purple targets. See how many levels you can complete!

Here's Wacky Cannon!

Play My Code is a place where you can create your own online games easily using the site's Quby language. The games are compiled into native JavaScript, compatible with all modern HTML5-compliant browsers. Once you've written a game, you can embed it on your website or blog, like I have done above. It's like YouTube, but for games! So, if you think you've got a game in you, head over to Play My Code and write one.

Click here to see all my games, including the popular Chain Reaction!

Did you like Wacky Cannon? Share your thoughts in the comments below.

Related posts:
Play My Code: Chain Reaction

stackoverflow - 30k rep

Seven months after crossing the 20k milestone, I've now achieved a reputation of 30k on stackoverflow! The following table shows some interesting stats about my journey so far:

	0-10k	10-20k	20-30k	Total
Date achieved	01/2011	05/2011	01/2012
Questions answered	546	376	253	1175
Questions asked	46	1	6	53
Tags covered	609	202	83	894
Badges (gold, silver, bronze)	35 (2, 10, 23)	14 (0, 4, 10)	33 (2, 8, 23)	82 (4, 22, 56)

As I mentioned before, I have really enjoyed being a member of stackoverflow. For me, it has not simply been a quest for a high reputation, but more about learning new technologies and picking up advice from other experts on the site. I like to take on challenging questions, rather than the easy ones, because it pushes me to do research into areas I have never looked at before, and I learn so much during the process.

I have to admit, I haven't spent much time on stackoverflow recently. I've been busy at work and also took up three Stanford online courses which I completed at the end of last year.

Now let's see how fast I can make it to 40k!

Stackless Exceptions for Improved Performance

One of the reasons for standard exceptions being slow is that they have to fill in the execution stack trace for the current thread. Although, this is useful for debugging, in most cases you don't really care about the stack trace. What you care about is that an exception of a certain type was thrown and what the error message was. For example, a java.io.FileNotFoundException was thrown with message config.xml (The system cannot find the file specified)".

Stackless Exceptions are exceptions without any associated stack information. They are faster to create than normal exceptions because they don't record information about the current state of the stack frames for the current thread.

The class below is an example of a stackless exception. The fillInStackTrace method has been overridden so that it doesn't do anything and simply returns the current instance.

/**
 * An exception which does not fill in a stack trace
 * for performance reasons.
 */
@SuppressWarnings("serial")
public class StacklessException extends Exception {

    /**
     * Constructs a new stackless exception
     * with the specified detail message.
     *
     * @param message the detail message.
     * @see java.lang.Exception#Exception(String)
     */
    public StacklessException(String message) {
        super(message);
    }

    /**
     * Does not fill in the stack trace for this exception
     * for performance reasons.
     *
     * @return this instance
     * @see java.lang.Throwable#fillInStackTrace()
     */
    @Override
    public Throwable fillInStackTrace() {
        return this;
    }
}

I measured performance by comparing the time taken to create a million StacklessException and Exception objects. I found that the creation of stackless exceptions is nearly 40 times faster than normal exceptions.

You can then create more specific exception types which subclass StacklessException. For example:

public class PersonNotFoundException extends StacklessException {
    public PersonNotFoundException(String message) {
        super(message);
    }
}

As an aside, note that the JVM omits stack traces if an exception is thrown very frequently. This optimisation is enabled by default and can be disabled using the JVM option -XX:-OmitStackTraceInFastThrow.

fahd.blog in 2011

Happy 2012!
I'd like to wish everyone a great start to an even greater new year!

During 2011, I posted 58 new entries on fahd.blog. I am also thrilled that I have more readers from all over the world too! Thanks for reading and especially for giving feedback.

Top 5 posts of 2011:

• Useful Eclipse Templates for Faster Coding
• Java 7: Diamond Operator
• HTML5 Canvas - Bouncing Balls
• Java 7: Working with Zip Files
• Writing your own Bash Completion Function

I'm going to be writing a lot more this year, so stay tuned for more great techie tips, tricks and hacks! :)

Stanford's Online Courses: ml-class, ai-class and db-class

About three months ago, I signed up to Stanford's first-of-its-kind, free, online courses on Artifical Intelligence, Machine Learning and Databases. I have now successfully completed all three courses!

• The Artifical Intelligence (ai-class) class, led by Sebastian Thrun and Peter Norvig, covered probability, Bayes networks, machine learning, planning, Markov decision processes (MDPs), particle filters, game theory, computer vision, robotics and natural language processing. There were in-class quizzes, homework exercises and two exams.
• The Machine Learning (ml-class) class, led by Professor Andrew Ng, covered supervised learning (linear regression, logistic regression, neural networks, support vector machines), unsupervised learning (k-Means clustering), anomaly detection and recommender systems. There were in-class quizzes, review questions and programming exercises.
• The Introduction to Databases(db-class) class, led by Professor Jennifer Widom, covered relational databases, relational algebra, XML, XPaths, SQL, UML, constraints, triggers, transactions, authorization, recursion and NoSQL systems. There were in-class quizzes, assignments, including practical exercises (such as creating triggers, writing SQL or XPaths that would run on a set of data) and two exams.

Even though I had studied these topics a long time ago at university, I found it really useful to refresh my memory. They took up quite a bit of time (about 2 hours a week for each class), but it was definitely worth it.

I am now looking forward to starting some new classes in 2012!