CS 535 Object-Oriented Programming & Design Spring Semester, 1999 Comments on the Programs
	Previous    Lecture Notes Index         © 1999, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 11-May-99

References
Names
Code Presentation
Documentation
Parameters verses Fields
Java’s Return Problems
Some Translator Solutions

References

Doc 20, Comments on the Programs Slide # 2

Names

Code Presentation

If you use tabs to indent your code, then always use tabs. By always I mean every line of code in your program uses tabs and no spaces for indentation.

If you use spaces always use spaces and always use the same number of spaces.

if (x == y )
   {
   if (z == w )
      blah
else
   whereDoesThisGo?
   }
Doc 20, Comments on the Programs Slide # 3

Documentation

public class Translator
   {
   HashMap dictionary = new HashMap();

public void addWords(String key, String words )
   {
   Vector words = new Vector();
   StringTokenizer parser = new StringTokenizer( words, "," );
   while (parser.hasMoreTokens)
      {
      String word = parser.nextToken();
      words.add( word);
      }
   
   dictionary.put( key, words );
   }

Doc 20, Comments on the Programs Slide # 4

Parameters verses Fields

public class Translator
   {
   private String aValue;
   public void bar()
      {
      blah;
      blah;
      aValue = result of some computation;
      foo();
      more blah;
      }
   private void foo()
      {
      String myData = aValue;
      Compute on myData;
      }
   }
Doc 20, Comments on the Programs Slide # 5

Java’s Return Problems

Given a method isValid( String value ) we want to return two pieces of information:

Boolean result

If it is not valid a reason

Java supports only one return type

Java supports only pass-by-value

boolean isValid( String value, String reasonInvalid )
   {
   if ( value is not valid )
      {
      reasonInvalid = "A reason";
      return false;
      }
   else
      return true;
   }

Doc 20, Comments on the Programs Slide # 6

public class Foo
   {
   private String reasonInvalid;
   
   public boolean isValid( String value )
      {
      if ( value is not valid )
         {
         reasonInvalid = "A reason";
         return false;
         }
      else
         return true;
      }
   
   public String getReason()
      {
      return reasonInvalid;
      }
   }
Doc 20, Comments on the Programs Slide # 7

public class Foo
   {   
   public boolean isValid( String value )
      {
      if ( reasonNotValid( value ) == null )
         return true;
      else
         return false;
      }
   
   public String reasonNotValid( String value )
      {
      if ( value == null )
         return "null not allowed" ;
      else if ( value.length() == 0 )
         return "empty strings not allowed";
      else
         return null;
      }
   }

Doc 20, Comments on the Programs Slide # 8

public class Foo
   {   
   public boolean isValid( String value, Reason explain )
      {
      if ( value == null )
         {
         explain.text = "null not allowed";
         return false ;
         }
      else if ( value.length() == 0 )
         {
         explain.text = "empty strings not allowed";
         return false ;
         }
      else
         return true;
      }
   }
Doc 20, Comments on the Programs Slide # 9

public class Foo
   {   
   public void validate( String value)
      {
      if ( value == null )
         throw new NotValidException( "null not allowed");
      else if ( value.length() == 0 )
         throw new NotValidException( "empty strings not allowed");
      }
   }

Doc 20, Comments on the Programs Slide # 10

Some Translator Solutions

English to German

Spanish to English

Spanish to English to German

Doc 20, Comments on the Programs Slide # 11

public interface Translatable
   {
   public String translate( String word );
   public boolean contains( String word );
   }
public class OneStepTranslation implements Translatable
   {
   HashMap dictionary = new HashMap( );
   
   public String translate( String word )
      {
      return (String) dictionary.get( word );
      }
   public boolean contains( String word )
      {
      return dictionary.containsKey( word );
      }
   
   }

Doc 20, Comments on the Programs Slide # 12

public class TwoStepTranslation implements Translatable
   {
   OneStepTranslation foreignToEnglish = new OneStepTranslation( );
   OneStepTranslation englishToForeign = new OneStepTranslation( );
   
   public String translate( String word )
      {
      String englishTranslation = foreignToEnglish.translate( word);
      return englishToForeign.translate( word );
      }
   public boolean contains( String word )
      {
      if (! foreignToEnglish.contains( word ) )
         return false;
      String englishTranslation = foreignToEnglish.translate( word);
      return englishToForeign.contains( englishTranslation );
      }
   }

Doc 20, Comments on the Programs Slide # 13

public class Word
   {
   /**
    * Keys = languages as strings
    * Values = Set of strings, each string is a translation
          of this word into the give language
    */
   HashMap translations = new HashMap();
   public boolean containsLanguage( String language )
      {
      return translations.containsKey( language );
      }
   public Set translateTo( String language )
      {
      return (Set) translations.get( language );
      }
   public void addTranslation( String language, String text )
      {
      String[] newTranslation = { text };
      addTranslations( language, newTranslation );
      }
   public void addTranslations( String language, String[] text )
      {
      if ( !containsLanguage( language ) )
         translations.put( language, new TreeSet() );
      Set existingTranslations = (Set) translations.get( language );
      List newTranslations = Arrays.asList( text );
      existingTranslations.addAll( newTranslations );
      }
   
   public Set languages()
      {
      return translations.keySet();
      }
   }
Doc 20, Comments on the Programs Slide # 14

public class WordIndex
   {
   /**
     * keys = Strings of the format lanuage@text. For
              example english@mother
     * Values = Word objects that contains translation of the text
              into other languages
     */
   TreeMap languageWordIndex = new TreeMap();
   
   private static final String LANGUAGE_TEXT_SEPARATOR = "@";
   
   public void add( Word newWord )
      {
      Set languageSet = newWord.languages();
      
      Iterator languages = languageSet.iterator();
      
      while ( languages.hasNext() )
         {
         String language =  (String) languages.next();
         add( language, newWord );
         }
      }
   
   public boolean contains( String language, String text )
      {
      return languageWordIndex.containsKey( key( language, text ));
      }
      
   public Word get( String language, String text )
      {
      return (Word) languageWordIndex.get( key( language, text ));
      }
   
   private static String key( String language, String text )
      {
      return language.toLowercase().trim() + 
         LANGUAGE_TEXT_SEPARATOR + 
         text.toLowercase().trim();
      }
      
   private void add( String language, Word newWord )
      {
      Set translationSet = newWord.translateTo( language );
      
      Iterator translations = translationSet.iterator();
      while ( translations.hasNext() )
         {
         String aTranslation = (String) translations.next();
         languageWordIndex.put( key( language, aTranslation), 
                                    newWord);
         }
      }
   }
Doc 20, Comments on the Programs Slide # 15

Previous    visitors since 11-May-99