DevFright

Update – 4 April 2025. A new version about Swift can be found in What is a Class in Swift.

A class in Java can be thought of as a blueprint. If using Karel the Robot as an example, each time we “extend Karel” we are getting a copy of Karel the robot to utilise. The blueprint specifies exactly what Karel can do out of the box. In terms of Karel, the blueprint is held at Stanford and we are not able to modify him. Every person who takes the iTunes U CS106A course takes a copy of Karel each time the program runs. The reason we cannot modify the blueprint is that changes we make would likely break everyone elses programs.

So what we do is become a subclass of Karel… ie, we “extend Karel” which means that our programs make an exact copy. When I use the word subclass, this is the opposite of superclass which is what Karel is to our own implementation. This doesn’t mean that ours is on a lower level… in fact, it could be said that we have more power being a sub-class because we get a copy of Karel and can enhance him with a turnRight() private method. So, our copy of Karel can do more than the blueprint specifies.

How to Create a Karel Subclass

Creating a class of Karel is quite simple. Our code needs a few things for it to work though. The first important line is the import which lets the program know where the blueprint is stored. In the case of Karel, this is held at Stanford at the location on line 1 of the code:

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Update: These notes are very old now, from back in 2012/2013. The course still exists at Stanford, but I would suggest visiting there to get the latest information.

Lecture 1 of CS106A was an introduction to the course which covered what things you will be learning over the next 10 or so weeks. It also included details which are needed to complete the course. You can find my notes over here and as well as my suggestions on how to work on iTunes U with no official dead lines and no one to report back to.

Lecture 2 is where the course starts to get interesting. In this lecture you get to see a program being written from scratch as well as successfully run. You also get to see how a basic program is designed as well as an explanation of why you need to write it with a specific style. After the simple program demonstration, the difficulty level gets notched up very slightly and a demonstration of a program with loops and control statements is used.

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Updated April 2025.

This article was originally published back in December 2012 and referred to a robot called Karel that was used in a Stanford programming course I followed in iTunes U. Although Karel was great at the time, and probably still is, it’s time to update this article.

Control Statements are found in any programming language and provide a way for the code to run differently based on conditions, wether that be a screen tapped, a time elapsed, a list created, and so on. You will see them through out your code.

Although control statements exist in any programming language, we’ll use the Swift syntax to work with them, given that this is a Swift programming blog.

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Update 2025 – I do not know if Karel still exists. This page is here because I don’t want to delete it.

Karel the Robot was created in the 70s by Rich Pattis. It/he was designed to help beginners learn how to program without all the additional complexities that programming languages bring. By cutting back to basics, it allows the simple things to be learned first such as the structure of programming as well as the preciseness of coding.

I mentioned in my CS106A lecture notes that Karel lives in a grid and has a few limited capabilities such as being able to move forwards, turn left and carry a bag of beepers as well as pick beepers up and put them down. He can also not pass through walls. His little world doesn’t necessarily need to be little and can be custom built to whatever size and have various walls put around the world.

Karel the Robot now runs in Java and works in the Eclipse development environment which makes it handy for when you move later on in CS106A to a regular version of Java.

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Update: These notes are very old now, from back in 2012/2013. The course still exists at Stanford, but I would suggest visiting there to get the latest information.

Today I viewed lecture 1 of the Stanford CS106A course on iTunes U. No programming was done on this introductory lecture but instead, a lot of details about the course, about what will be learned as well as a number of items relating to the students at Stanford who actually take the course.

Although I have made a lot of notes, I wont be going in to detail on some of the points as parts of the lecture relate to students at Standford only.

Prerequisites of CS106A – ie… what do you need to know?

For those who haven never programmed before, you’ll be glad to learn that there are no prerequisites at all for this course, other than the lecturer hinting that it would be good to know how to switch a computer on.  As no experience is needed, that means that most people should be able to work through this course although I’d expect that those wanting to take the course will have a reason for wanting to take it and therefore, might have some background.

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Updated 2 April 2025

Over the past 13 years I have worked with and still am learning programming. I began with iTunes U with the CS193p course from Stanford University, as well as others listed below.

In my Hello World post written back in December 2012, I wrote that I wanted to learn how to create apps for the iPhone. As well as the mentioned CS193p course, which is still updated, the latest being 2023, and still taught by Paul Hegarty, who does an amazing job. Just prior to going through that course I went through CS106A, CS106B, CS107. I am happy to say that I have been creating iPhone apps over the years, although I have also worked with other languages such as PHP, C#, .NET, Python, JavaScript/TypeScript to name a few. What I enjoy the most is iPhone app development.

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Update 2025: It has been a good number of years since I wrote this article, originally written December 2012. Since then I worked more with Objective-C, then moved to Swift and then SwiftUI. In between all of that I began studying remotely at BYU Idaho learning software engineering. I also worked with PHP, JS, TS, Python, C# and .NET, and now back to PHP and SwiftUI.

Original Post

Over the past 11 months I have been learning how to program. I started off with Java and went on to C++ and then to Objective-C. This site exists for me to document what I learned in the lectures as well as some tips and sample code to help you find answers to programming questions/techniques that you are struggling with.

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