SEG 3550 Fundamentals of Information System

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SEG 3550 - Fundamentals of Information System

• Tutorial 9 Programming Style and Demo
• By Henry P.S. Hui

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Outline

• Programming Style
• Demo
• Java application with JDBC
• ProC application

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Programming Style

• Writing program is far more easy than writing
  good program
• Definition of Good
• Easy to follow by other programmers
• Efficient use of memory
• Effective code reuse
• (many others)

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Both C/C and Java

• Some techniques that share between C/C, Java
  and also some other languages

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Boolean and Integer

• A boolean variable takes the same byte size as
  integer
• However, boolean only give two output
• Integer can give many different
• Conclusion
• Integer is more informative without any
  additional lost
• Use int to replace boolean especially as a return
  type
• Can use to specify the condition of the output
• Normal / if error, what type of error

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Understanding different errors

• Segmentation Fault
• Illegal access of memory
• Usually is the problems of pointers or
• Reference of variables that have no assigned
  value
• Bus Error
• Access of physically not exist memory address
• Pointer contain being alter by other operation

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Reading the reference type

• Read in reverse direction
• char nameList 0
• An array of pointers which only points to char
• Array reference is the same as pointers

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DEBUG Label

• Define a variable DEBUG
• Put all the debug statement into the condition
  score under DEBUG
• if(DEBUG)
• Quite and easy way to identify the debug message
• When the development is completed, simple set it
  to false or 0, then everything gone

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Writing debug message

• Common debug messages
• Die!!!!
• Help
• Completely not meaningful
• Better way
• ERRORClassName.FunctionName Description
• Descrption should describe what have been done
  therefore the code get into this error message

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Static or not static?

• Static member
• Share among class
• Can be access by all objects of the class
• Non-static member
• Share within the instance of object created
• If the member representing the same thing for all
  object of the class ? Static
• Caution! Can be changed by different objects

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Function Call

• Each function call will need to create a new
  stack for the execution
• Type of stacks
• Control stack
• Execution stack
• Function stack
• Run-time stack
• Recursive function is not efficient
• Recursively creating Activation Records

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Activation Records

• Contain stack pointers, frame pointers
• Problem is it will hold up a bigger and bigger
  memory size in the system

AR1
AR 2
AR 3
AR 4
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Structure of the program

• Some of the action in the program is critical
• E.g. Action that changes the database
• Use a single entry scheme
• All the function that do such action will call a
  single function
• This function need to be very generic
• Can be used to log the action items

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Java

• Starting from import
• Dont import the entire package
• Unless you have used more than three classes
• This can reduce the preloaded memory

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StringBuffer

• String sql select from table namelist where
  id id and name name
• 5 strings are actually created in the memory for
  this line of code
• Have to wait the garbage collector to collect the
  unused memory
• Using StringBuffer can reduce this problem
• More trouble but more efficient in memory
  utilization

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E.g. of using StringBuffer

• StringBuffer sql_sb new StringBuffer()
• sql_sb.append(select from table namelist where
  id )
• sql_sb.append(id)
• sql_sb.append( and name )
• sql_sb.append(name)
• sql_sb.append()
• String sql sql_sb.toString()

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Exception Handling

• Handle specify exception
• Handle IOException and SQLException
• But not Exception
• Catching specify exception give more information
  on the error
• Can use a catch all at the outer scope to prevent
  the system to exit without attention or log

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Try-Catch-Finally

• Try-catch block is commonly used for handle
  exception, but the finally block
• Finally block will be executed whenever the code
  of the try block is executed
• Useful for clear up the instances created in the
  try block
• E.g. Stream opened in try block and error in the
  middle, use finally block to close it

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Static initialization Block

• Any block with the label static is a static
  initialization block
• A java program without main(String arg)
• public class DemoClass
• static
• System.out.println("hi")
• System.exit(0)

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IO in C

• Use Exclusively the C library instead of C
  C
• printf or iostreamObjectcout ltlt
• The application will be more efficient

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Variable definition

• Set a value to a variable is declared
• Java will assign a null to it by default but
  not in C/C
• If we do not assign value to the variable when we
  declare it, problem will exist, e.g.
• char testString
• printf(s\n, testString)

Random outputMay have segmentation fault
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Demo

• The code is just to show you what have been
  taught in the previous tutorials works
• The style of the code is not considered in the
  example demo code