Monday, 14 March 2016

Static vs Non-static in Java

A really good (and tough!) distinction that everyone coding in Java needs to know: the difference between static and non-static variables in Java.

In my opinion, tutorial4us did a great job explaining it. A very good read indeed.

My understanding is that instance (non-static) variables exist in each object (instance of the class). Each object will have its own value/content for each instance variable. Think of the name in a Person class. We define the name as an attribute or property of a person, and each Person object will have its own name.

Static variables exist only inside the class where they are declared. Some call them "class variables" because they are bound to the class, not the object. They are unique and when a new object is instantiated, the object does not get its own copy of it. Rather than using the dot notation with the object (object.nnnn), you would use it with the class (Class.nnnn).

Note that this also applies to, and is also often used with methods!

Think about these example:


public class Test
{
  public static void main (String args[])
  {
    int[] numbers = {1,2,3,4,5};
    System.out.println( numbers.length ); // =5
    // length (size/number of elements) of the array object
    System.out.println( Math.PI );
    // PI is stored as a static constant inside the Math class
    // we don't need to instantiate a Math object to use PI
  }
}

To code or not to code

...For some of us, that is the question!

One of my favourite authors, V. Anton Spraul, has an interesting website about his books, programming, computer science, and other topics.

What caught my attention (this time) is the Learning How to Program: A Guide section of his web site.

I would like to recommend reading part two, "How do I know if programming is for me?" to anyone considering a CS course, diploma or degree, job, or anything that involves coding.

Below are my favourite quotes from the points he makes:

  • "A good programmer enjoys programming. I don't mean that every act of coding will bring unbridled joy, or that programming is fun in the same way that playing a favorite sport or video game is fun. But there should be a real pleasure in seeing one's program working, even if the program is a pitiable little thing that accomplishes almost nothing."
  • "Probably just about anybody could become a pretty good programmer if they work hard enough to become one. But make no mistake about it, programming is tough mental work. If, on some level, you're not enjoying the work, you're never going to be able to focus on it long enough to master it."
  • "Unfortunately, just because a person really enjoys working with computers doesn't mean he or she will enjoy programming. I guess the reverse is true, though; if you don't like technology, you probably shouldn't try to learn programming."
I couldn't have put it better myself. Thanks again, Mr. Spraul.

Friday, 4 March 2016

Thursday, 3 March 2016

this Java keyword

A feature of Java that usually confuses beginners is the "this" prefix.

In a nutshell, the this keyword is used to distinguish between parameters of a method and attributes (instance variables) of a class.

The following link will lead you to a web page that does a great job contrasting and explaining this with examples:

Sunday, 7 February 2016

Distribute your Java classes in a JAR file

The source of the information given in this post is http://www.skylit.com/javamethods/faqs/createjar.html
In my opinion, the simplest and quickest way to do this is using the command line.


Steps
  1. Start the Command Prompt. The easiest way is to Shift-Right Click on an empty spot in your Windows (File) Explorer. Make sure no files are selected, though. The idea is that your Windows Explorer should be in the location of your Java files.
  2. Navigate to the folder that holds your class files:
    Copy the path from Windows Explorer's address bar (more details about WE here), then type the following into the command prompt window:

    cd /d 
  3. minding the space at the end, then paste the path that you copied from Windows Explorer's address bar. Press Enter.
  4. If you haven't set your path to include JDK’s binaries (compiler and utilities, including the one that creates jar files), you need to do so by adding it to your default path (your folder may differ depending on the version of the JDK that you installed)
    path %path%;C:\Program Files\Java\jdk1.8.0_83\bin
  5. Compile your class(es):
    javac *.java
  6. Create a manifest file and your jar file (Replace IA with the relevant name to your project):
    echo Main-Class: IA > manifest.txt
    jar cvfm IA.jar manifest.txt *.class
    ---- or ----
    jar cvfe IA.jar IA *.class
  7. Test your jar:
    java -jar IA.jar
  8. Create a batch file so your end user can double click on it to run your command line application (you may also use Notepad to do this):
    copy con run.bat    (creates the file)
    java -jar IA.jar    (Press CONTROL Z and Enter to finish and save the file)
  9. Double click on run.bat to test it.

Thursday, 28 January 2016

IBDP Computer Science IA

Important information about the
IBDP Computer Science Internal Assessment

Screencasting & File Requirements

Mac:
Windows:
Ensure that your screencast is about 5 minutes long, and in MP4, MOV, M4V format;
Maximum size 500 MB

Formatting of work for IBDP Computer Science IA

  • Arial font size 12 (where the language / script supports it)
  • Double-line spacing
  • Numbered pages
  • Portrait orientation (rather than landscape) – except where it is necessary to accommodate a specific item such as a graph or illustration
  • DOC, DOCX, PDF or RTF

Optimise Windows 10/11

How to optimise your Windows setup Just in case you need it. If you want a safe and conservative approach, just disable the background apps ...