CS101-CS102

Java Lab - Design & Implementation

Details & examples of what we expect in Java (structured programming) lab assignments...

Structured Programming Designs

• Top-down design: ensure that a main algorithm of at most seven steps is written & checked before any attempt to solve these steps is made. Given independent implementations of the pieces, would the design be guaranteed to work correctly?
• Fully specify steps: Each step in an algorithm should be complete, such that it could be given to someone (who knows nothing of the original task) and they could correctly implement it without any additional information. This requires information that will be input to and output from the step, to be clearly specified.
• Data/Memory requirements: Information flowing from one step in the algorithm to another should be identified. In the algorithm, the word/phrases involved should be underlined. These are the memory locations needed by your program. Their types and whether they are variables or constants (and if constants, their values) should be clearly specified.
• Rewriting/expanding steps is simply a rewording of the step and must not do something else or include anything not mentioned in the original step!
• Beginners should develop algorithms until one step corresponds to one Java statement.

Basic Algorithm Steps

Ultimately, you should aim to have an algorithm comprising only sequence/decision/repetitions of input/output/assignment steps. These correspond to the following common English sentence forms.

• sequence ( "do this and then do this and then do this..." )
• decision ( "if condition then statement else statement")
• repetition ( "while condition do this" or "do this while condition" or "for each/every/all/no-of-times do this" )

• input ( "ask for and get x" or "read/input/get x" )
• output( "print/report/output x" )
• assignment ( "x is 0" or "x is square root of y" ... )

Important: note that there is no statement/sentence of the form "go to step x". Such forms are a remnant of the older go-to (spaghetti code) paradigm and must be rewritten using one of the structured programming paradigm forms below.

The correct form of the various control algorithm forms is:
(notice how they correspond one-to-one with the Java statements!)

1.    do this 
2     do this
3.    do this 

1.    do this 

2     if condition then 
2T.1     do this 
2T.2     and this
      else 
2F.1     do that
2F.2     and that 

3.    do this 

1.    do this 

2     while condition do 
2.1      something 
2.2      and something more 
2.3      and yet more 

3.    do this 

1.    do this 

2     do 
2.1      something 
2.2      and something more 
2.3      and yet more
      while condition 

3.    do this 

1.    do this 

2     for each value of i from 0 to number of repetitions do
2.1      something 
2.2      and something more 
2.3      and yet more

3.    do this 

Algorithm development examples:

• The perfect number example, 
• The exam average problem

Also, be sure you are not making any of these Common Algorithm Development Mistakes

Methods

Any step in your algorithm may be implemented as a method. You should already be identifying the data/memory/variable locations used in each step as being  I(nput), O(utput) or L(ocal) to the step, so the only additional consideration is what name you want to give it! Write the algorithm for the method separate from the other parts of your design and then simply "call" -use/refer- to it as necessary (in exactly the same way you already call/use/refer to Java methods such as those for input, output and square roots!)

Implementation

• All programs should have a header comment, including a description, author name, date, etc.
• Comments should be used to aid understanding major sections of the code & to clarify non-obvious algorithms.
• Blank lines should separate all logical sections, ie. major steps, method definitions, etc.
• Correct indention must be maintained everywhere.
• All variables, constants, methods, and classes must be meaningfully named & follow Java naming conventions.
• Variables and named constants should be declared before the program code begins, not as needed in the program!
• Each variable or constant should be declared on a separate line.
• Named constants should be defined before variables so they are easy to find and change.
• Variables should not be initialised when they are declared, but only later given a value as necessitated by the algorithm.

When implementing your program in Java you MUST follow our Java Style Guidelines!

Last updated: 02 Oct 2010
Please report any errors or omissions to the course instructor.