	CS 580 Client-Server Programming Fall Semester, 2000 Hinges
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Contents of Doc 2, Hinges

References
Design Patterns for Object-Oriented Software Development , Pree, Addison-Wesley, 1995

SDSU Java Library, http://www.eli.sdsu.edu/java-SDSU/docs/


Doc 2, Hinges Slide # 2

Hinges

Software is not arbitrarily adaptable

One can not modify existing software arbitrarily

Can add places designed to change

These spots can be though of as hinges or hot spots

Changes at one of these hinges is relatively easy

Changing software in other locations or ways tends to:

break the system
be expensive


Doc 2, Hinges Slide # 3

Force

Adding correct hinges makes a program easier to modify

Counter-Force

There is a cost to building hinges
Hinges can make the software hard to understand
Hard to predict which hinges will be needed

When in doubt keep it out


Doc 2, Hinges Slide # 4

Hinge Example - Constants

Program that uses course numbers

class Example extends Frame 
   {
   public Example()
      {
      setTitle( "Hinge Example" );
      resize( 100, 100 );
      setLayout( new FlowLayout() );
      add( new Button( "CS 596") );
      show();
      }
   
   public boolean action( Event processNow, Object buttonPressed )
      {
      if ( buttonPressed.equals( "CS 596" ) )
         System.out.println("Pressed");
      return true;
      }
   }


Doc 2, Hinges Slide # 5

First Hinge

class Example extends Frame 
   {
   
   String courseName = "CS 596";
   
   public Example()
      {
      setTitle( "Hinge Example" );
      resize( 100, 100 );
      setLayout( new FlowLayout() );
      add( new Button( courseName ) );
      show();
      }
   
   public boolean action( Event processNow, Object buttonPressed )
      {
      if ( buttonPressed.equals( courseName ) )
         System.out.println("Pressed");
      return true;
      }       
   }
Doc 2, Hinges Slide # 6

Another Hinge

class Example extends Frame 
   {
   String courseName;
   
   public Example()
      {
      try
         {
         ASCIIInputStream  cin = 
            new ASCIIInputStream( 
               new BufferedInputStream (
                  new FileInputStream( "ExampleConfig" )) );
         courseName = cin.readWord() + cin.readWord();
         
         setTitle( "Hinge Example" );    resize( 100, 100 );
         setLayout( new FlowLayout() );
         add( new Button( courseName ) );
         show();
         }
      catch ( FileNotFoundException noFile )
         { System.out.println( "No Config file"); }
      catch ( IOException readError )
         { System.out.println( "Read Error"); }   
      }
   
   public boolean action( Event processNow, Object buttonPressed )
      //Same as before
}
Doc 2, Hinges Slide # 7

ExampleConfig Contents

CS 569

This is a Hinge?
How safe?

How extendable?


Doc 2, Hinges Slide # 8

Some Hinge Oil

sdsu.util.ProgramProperties

Parses

Configuration files
Command line arguments

Command Line argument

-flag=value
-flag value
-flag
--xyz
--

File Formats

properties format #A comment to the end of the line key1=value1 key2=value2 with spaces key3 with spaces=value3 #part of the value

sdsu.util.LabeledData format #A comment to the end of the line, key1 = value1; key2='value2 with spaces'; 'key3 with spaces'=value3; # a comment


Doc 2, Hinges Slide # 9

Simple Example

import sdsu.util.ProgramProperties;
public class ConfigurationExample {
   public static void main(String args[]) {
      try
         {
         ProgramProperties flags = 
            new ProgramProperties( args, "configurationFile");
         String nameValue = 
            flags.getString( "name" , "No name given");
         int size = flags.getInt( "size", 0);
         boolean switchOn = flags.containsKey( "s");
         System.out.println( " nameValue: " + nameValue);
         System.out.println( " size: " + size);
         System.out.println( " switchOn: " + switchOn);
         
         }
      catch (java.io.IOException readParseProblem)
         {
         System.err.println( "Program aborted on error " + 
         readParseProblem);
         }
   }
}

File "configurationFile.labeledData"

name=Roger;
size=12;
Doc 2, Hinges Slide # 10

Sample Runs
java ConfigurationExample

Output nameValue: Roger
size: 12
switchOn: false

java ConfigurationExample -s -name Pete

Output nameValue: Pete
size: 12
switchOn: true

java ConfigurationExample -conf=otherFile

Output nameValue: Sam
size: 8
switchOn: true

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2000 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA.
OpenContent license defines the copyright on this document.

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