Mark's IT Blog

This weeks lecture was presented by Michael Smith and targeted an introduction to testing and debugging. Initially was discussed when testing should begin in the Software Development process, the Design phase. As soon as the solution has been designed then tests for that solution can and should also be designed. During the implementation phase testing should be conducted as soon as compilation is complete. Documentation was also recognized early in the lecture as a key aspect of testing and debugging.

Pearl Of The Week: Types of errors in Programs:

• Syntax Errors -> Mistakes in spelling or unclosed parenthesis etc. Compiler will find these errors, preventing completion of compilation until they are amended.
• Execution/Run Time Errors -> Null Pointer Exceptions, Attempting to access arrays outside of bounds. Occurrence of these errors in Java will result in relevant exceptions thrown.
• Logic Errors -> Project has been compiled and runs without error but behavior is not as expected.

We then explored some examples of how important testing and debugging is by reviewing some examples where the process was not done correctly.

Week 4’s lecture by Judy got slightly deeper into the concept, design and implementation of objects. Again, I am finding that these lectures are moving very slowly and feel that prospective students should be given a chance (if they want) to demonstrate that they are not complete novices. However, this from an administrative point of view would probably be impossible and running through an introductory class will ensure that all the basic concepts (and more importantly, conventions) are clearly understood. So the only thing to do is get good marks and have a point to argue from for next semester.

The lecture started of defining the terms Abstraction and Modularization referencing their relevance to programming with a simple clock program. I felt this was valuable but could have been so much more valuable if we had gone a few steps further and show the practical applications for modularization and decoupling by making the clock program work and re-using the modules in different examples. In this example, Class Diagrams and Object Diagrams where covered (straight out of bluej).

Next came Primitive Types vs Object Types, specifically the differences in memory allocation (objects reference). I guess this will be a more interesting point when programming in C and the Garbage collector does not destroy unreferenced variables. Formal Parameters, Actual Arguments, Internal and External method calls followed, these were all consistent with what I have seen previously  and now feel very intuitive. The only point where I felt uncomfortable was where methods contained local variables with the same name as their Formal Parameters, necessitating the need for this.variable = variable notation. Seems much easier to me to avoid double naming.

The really key topic covered in the lecture and in the tutorials was the coding conventions: 70.40.214.44/Java_coding_standards.pdf

I need to update my existing habits to meet these standards (definitely a good thing).. means alot more indenting.

I will start reading through the text book more for this subject and continuing my own Java development. This should suffice until next semester or the 3rd when I hope we have the chance to do some challenging implementations.

Pearl of the Week: My first attempt at using Java Objects and a MySQL DB, hope to learn how wrong it is in the near future.

Haha there already a few bit there that are breaking format conventions already…. D:

Note, for some reason the code box is automatically removing indentation. The code box was made using a WordPress plugin: http://kpumuk.info/projects/wordpress-plugins/codecolorer/

Judy Sheard’s third week lecture continued on the introduction to Java and programming as a whole. Although all of the concepts covered were very basic some of the terminology needs to be learned, particularly for when in the work place and the need to communicate arises. So, a summary of the terms covered and their contextual definitions:

• Selection – if construct, 3 components: condition,consequent, alternative. if(keyword) (condition){consequent}else{alt}
• relational operator –  ==, !=, <, >, <=, =>  result of these operators is a boolean TRUE/FALSE
• boolean expression –  using one of the above operators.
• compound statement – multiple lines in consequent block.
• nested if – if within and if construct.
• logical operators – !, && , || NOT, AND, OR can be used in conjunction with boolean expressions.
• switch statement – can be used to neaten cascading if statements (compiles as cascading ifs however) ideal for day of the week statements etc. Can only be used with int and char expression evaluations.
• shorthand arithmetic operators – a += 1; a -=1; a *=2; a /=3; a %=5; //reassign a with the result of the operators. a++; ++a; b–; –b; // if ++, — is after the variable then the arithmetic will be applied after the entire statement.
• local variables –  variables within methods which exist only as long as the method is being executed.
• base input –  using scanner method to read from keyboard

Precedence rule for evaluating expressions (JAVA):

1. Parenthesis
2. Unary Operators (++, –, !)
3. Binary Arithmetic Operators (*, /, %, +, -)
4. Relational Operators (<, >, <=, =>, ==, !=)
5. Logical Operators ( &&, ||)
6. Shorthand arithmetic ( =, +=, -=, *=, /=, %=) // these ones are evaluated right to left.

When in doubt of any of the above its much easier just to use parenthesis…

Pearl of the week: (I was always under the impression that a leap year is simple every 4th year, this is not the case however)

Algorithm for leap years:

if (year modulo 4 is 0) and (year modulo 100 is not 0) or (year modulo 400 is 0)
       then is_leap_year
else
       not_leap_year

Hope all banking systems have this correctly coded otherwise the 2100 bug might turn out to be more exciting than y2k.

The tut again was simply a revision of the lecture with the chance to ask question and get explanations. We are getting the assignment outline this week, Judy has said it is not really challenging…

if (year modulo 4 is 0) and (year modulo 100 is not 0) or (year modulo 400 is 0)
       then is_leap_year
else
       not_leap_year