I just wrote about what a class is, in basic terms for those beginning on the CS106A course at Stanford on iTunes U. The next item I want to cover is what a method is.

What is a Method?>

Java allows you to create methods. In simple and beginner terms (meaning those working on programming with Karel), a method is a set of instructions that can be called on by name to execute. In a few of my previous posts I have already written about methods although I haven’t taken the time to explain exactly what a method is. [Read more…]

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: [Read more…]

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. [Read more…]

When programmers write code, they tend to stick to an indentation style which essentially makes the program easier to read. When programs get more complex, there are often a number of lines of code which contain loops within loops amongst other things. If all code was written starting at the left edge of the page for every line, it would quickly become unreadable. Take the following example:

import stanford.karel.*;
public class BeeperPickingKarel extends Karel {
public void run() {
move();
if (noBeepersPresent()) {
pickBeeper();
}
move();
}
{

Although this selection of code is relatively simple and with a bit of effort, is fairly readable, it is still recommended that you indent your code to make the blocks and other statements stand out. Indenting and adding more line breaks in the code above would produce the following:
[Read more…]

In chapter 3 of Karel the Robot, I have learned that Karel uses Control Statements. In chapter 2, Karel simply followed commands in order. Some of these commands were separated in to methods so that a single command could be used to issue several commands from a block, but in essence, Karel would do in order what you told him to do.

Control Statements change things in that you can tell Karel to do something based on a condition of his surroundings or based on a loop so he can do something while something else is true… such as “move forwards if there is no wall ahead”.

Conditional Statements

Two types of control statements are introduced in chapter 3 of Karel the Robot. The first type are called Conditional Statements. These are coded by using what is called the if statement. What this means is that a certain part of the program will run “if” a condition holds true. That condition could be something like “if Karel has beepers in his bag, run this section of code”. When his beepers run out, the program will then stop or move on to the next part.

Example:

if (condition) {
    statements put between the curly braces.
}

[Read more…]

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. [Read more…]

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. [Read more…]

I mentioned in my Hello World post that my goal is to learn how to develop apps for iOS devices (meaning the iPhone and iPad). To reach that goal I decided to check out the iTunes U courses for iOS and quickly landed on the CS193p course from Stanford University titled Developing Apps for iOS (Fall 2010). On loading up the course I see that the prerequisits are the CS106A, CS106B and CS107 which means I need to learn Java (CS106A), C++ (CS106B) and CS107 which covers several languages and the differences between them.

[Read more…]

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.

[Read more…]