CS 596: Client-Server Programming
Spring Semester, 1997
Doc 2 Pipes and Hinges

Pipes slide # 2
Hinges slide # 3

Some Hinge Oil slide # 8

Doc 2 Pipes and Hinges Slide # 1

References

Doc 2 Pipes and Hinges Slide # 2

Pipes

Doc 2 Pipes and Hinges Slide # 3

Hinges

One can not modify existing software arbitarily


Software has designated places where it is 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

Force

Designing hinges into a program makes the program easier to modify

There is a cost to building hinges

Too many hinges can make the software expensive and hard to understand

Doc 2 Pipes and Hinges Slide # 4

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 Pipes and Hinges Slide # 5

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 Pipes and Hinges Slide # 6

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 Pipes and Hinges Slide # 7

How extendable?

Doc 2 Pipes and Hinges Slide # 8

Some Hinge Oil

Parsing

Converts itself to and from strings

Read strings and streams

Allows whitespace and comments in strings representation

Automatically quotes special characters

User can define whitespace, separators, and quote characters

Parses command line flags

Flag syntax

-flag=value

-flag value

-flag

--xyz

--

Permits declaring default values

Doc 2 Pipes and Hinges Slide # 9

class LabeledDataExample
     {
     public static void main( String[] arguments)
          {
          LabeledData defaults = new LabeledData();
          defaults.put( "instructor", "Roger Whitney" );
          defaults.put( "courseName", "CS108" );
          
          String serialized = defaults.toString();     
          System.out.println( serialized );
          
          LabeledData refried = new LabeledData( );
          refried.fromString( serialized );
          System.out.println( refried.getData("courseName" ) );
          System.out.println( refried.getData("instructor" ) );
          
          OutputStream  cout;
          cout = new BufferedOutputStream ( 
                         new FileOutputStream( "test" ) );
          refried.save( cout );
          }
     }

Doc 2 Pipes and Hinges Slide # 10

# a comment, goes to the end of the line

instructor = 'Roger Whitney';      # 's are used keep name one string
courseName = 'CS 596';
courseLocation = ba254          # ; is a separator, not a terminator

public static void main( String[] arguments )
     {
     try
          {
          InputStream  cin = new BufferedInputStream (
                    new FileInputStream( "ExampleConfig" ) );
          LabeledData config = new LabeledData();
          config.load( cin );
          System.out.println( config.getData("courseName" ));
          System.out.println( config.getData("instructor" ));
          }
     catch ( IOException readError )
          {
          System.out.println( readError );
          }
     }

CS 596
Roger Whitney

Doc 2 Pipes and Hinges Slide # 11

class Example extends Frame 
     {
     String courseName;
     
     public Example()
          {
          LabeledData settings = readConfigFile();
          courseName = settings.getData( "courseName" );
          
          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 Pipes and Hinges Slide # 12

public LabeledData readConfigFile()
          {
          try
               {
               InputStream  cin = new BufferedInputStream (
                         new FileInputStream( "ExampleConfig" ) );
               LabeledData config = new LabeledData();
               config.load( cin );
               return config;
               }

          catch ( FileNotFoundException noFile )
               { 
               System.out.println( "No Config file");
               }

          catch ( IOException readError )
               { 
               System.out.println( "Read Error");
               }     
          }
     }// end class

Doc 2 Pipes and Hinges Slide # 13

Labels on data:

aid human reader

help insure proper reading of data

If absolute, multiple users cause problems

If relative, calling from different directorys is a problem

Others?

Need a better hinge

Doc 2 Pipes and Hinges Slide # 14

class LabeledDataExample
     {
     public static void main( String[] arguments)
          {
          LabeledData config = new LabeledData();
          config.fromCommandLine( arguments );
          System.out.println( config.getData("courseName" ));
          }
     }

java LabeledDataExample -courseName=CS596 -instructor Whitney


Output
CS596


Flag Options
-
flag=value-
flag  value-
flag                    (for last argument or next argument starts with - )--
zyx               (individual characters become separate flags)--
                    (ignore rest of the arguments)

Flags with no values are given value of LabeledData.NO_VALUE
Which is the string "_NO_VALUE"
Doc 2 Pipes and Hinges Slide # 15

class LabeledDataExample
     {
     public static void main( String[] arguments)
          {
          LabeledData config = new LabeledData();
          config.fromCommandLine( arguments );
          String name = config.getData("courseName", "CS108" );
          System.out.println( name );
          }
     }

java LabeledDataExample   -instructor Whitney

If the hashtable does not contain "key", then getData returns "defaultValue"

Doc 2 Pipes and Hinges Slide # 16

class LabeledDataExample
     {
     public static void main( String[] arguments)
          {
          LabeledData defaults = new LabeledData();
          defaults.put( "instructor", "Roger Whitney" );
          defaults.put( "courseName", "CS108" );
          
          LabeledData config = new LabeledData( defaults );
          config.fromCommandLine( arguments );
          System.out.println( config.getData( "courseName" ) );
          System.out.println( config.getData( "instructor" ) );
          }
     }

/* Constructs a new, empty labeledData object with the specified 
* default values.
*/
public LabeledData( LabeledData defaultValues )
Doc 2 Pipes and Hinges Slide # 17

class Example extends Frame 
     {
     String courseName;
     
     public static void main(  String[] arguments )
          {
          new Example( getProgramParameters( arguments ) );
          }
          
     public Example( LabeledData settings )
          {
          courseName = settings.getData( "courseName" );
          
          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 Pipes and Hinges Slide # 18

     public static LabeledData getProgramParameters( 
                                             String[] arguments )
          {
          LabeledData defaults = new LabeledData();
          LabeledData configFile = new LabeledData( defaults );     
          LabeledData parameters = new LabeledData( configFile );
          
          defaults.put( "configFile", "ExampleConfig");
          defaults.put( "courseName", "CS 596");

          paramaters.fromCommandLine( arguments );
          try
               {
               String fileName = parameters.getData( "configFile" );
               InputStream  cin;
               cin = new BufferedInputStream ( 
                         new FileInputStream( fileName ) );
               
               configFile.load( cin );
               }
          catch ( FileNotFoundException noFile )
               { 
               System.out.println( "No Config file");
               }
          catch ( IOException readError )
               { 
               System.out.println( "Read Error");
               }
          return parameters;     
          }
     }
Doc 2 Pipes and Hinges Slide # 19

class Example extends Frame 
     {
     String courseName;
     
     static String courseNameFlag = "courseName";
     static String configFileFlag = "configFile";
     static String windowTitleFlag = "windowTitle";
     static String windowWidthFlag = "windowWidth";
     static String windowHeightFlag = "windowHeight";
          
     public static void main(  String[] arguments )
          {
          new Example( getProgramParameters( arguments ) );
          }
          
     public Example( LabeledData settings )
          {
          setTitle( settings.getData( windowTitleFlag ));

          int width = Integer.parseInt( settings.getData(
                                              windowWidthFlag ) );
          int height = Integer.parseInt( settings.getData(
                                              windowHeightFlag ) );     

          resize( width, height );
          setLayout( new FlowLayout() );
          
          courseName = settings.getData( courseNameFlag );
          add( new Button( courseName ) );
          show();
          }
Doc 2 Pipes and Hinges Slide # 20

     public boolean action( Event processNow, Object buttonPressed )
          {
          if ( buttonPressed.equals( courseName ) )
               System.out.println("Pressed");
          return true;
          }           

     public static LabeledData getProgramParameters( 
                                             String[] arguments ){
          LabeledData defaults = new LabeledData();
          LabeledData configFile = new LabeledData( defaults );     
          LabeledData paramaters = new LabeledData( configFile );
          
          defaults.put( configFileFlag, "ExampleConfig");
          defaults.put( courseNameFlag, "CS 596");

          paramaters.fromCommandLine( arguments );
          try
               {
               String fileName = paramaters.getData( configFileFlag );
               InputStream  cin;
               cin = new BufferedInputStream ( new FileInputStream(
                                                        fileName ) );
               configFile.load( cin );
               }
          catch ( FileNotFoundException noFile )
               { System.out.println( "No Config file"); }
          catch ( IOException readError )
               { System.out.println( "Read Error"); }
          return paramaters;     
          }
     }

Doc 2 Pipes and Hinges Slide # 21

Designing hinges into a program makes the program easier to modify

There is a cost to building hinges

Too many hinges can make the software expensive and hard to understand

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 Pipes and Hinges Slide # 22

The balance between force and counter-force in school is off scale compaired to "real life", it is all counter-force