• Abstract Class:
  • A class without any instances
• Interface:
  • A set of services provided by a class

• Similarities:
  • Both can contain abstract methods
• Differences:
  • An interface only contains abstract methods
  • An abstract class can contain concrete methods

• When to use an abstract class:
  • You have several classes that provide the same functionality in the same way but you do not want to move that functionality into a concrete parent because it doesn't make sense to have instances of the parent
• When to use an interface:
  • You have classes that provide the same functionality in different ways and/or are not related hierachically
  • You need to reveal the capabilities of an object without revealing its class

• Abstract Classes:
  • AbstractButton : A generic button-like object in a GUI
  • AbstractCollection : A skeletal implementation of a class that contains a "set" of other objects
• Interfaces:
  • Comparable : Objects that can be ordered
  • ActionListener : Objects that can be performed of GUI actions (e.g., button clicks)

• Motivation:
  • The only way to get better is to practice
• The System to be Designed:
  • The Madison Music Machine 3000: A software implementation of a "karaoke machine" that can play (instrumental) music while simultaneously displaying the lyrics to be sung.

An Initial Design

An Improved Design

More Improvements

Eliminating the MadisonMusicMachine Class

Synchronizing the Music and Lyrics

Improved Synchronization

Adding a Presenter Interface

Combining the Lyrics and Music Classes

Adding a PlayList Class

AbstractLineElement

javaexamples/oopbasics/musicmachine/AbstractLineElement.java

/**
 * An element in a line of music
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public abstract class AbstractLineElement
{
    private int       durationInMillis, wholeNoteInMillis=1500;
    private String    value;
    

    /**
     * Get the duration of this element in milliseconds
     * (at the normal tempo)
     *
     * @return   The duration in milliseconds
     */
    public int getDurationInMillis()
    {
        return durationInMillis;
    }



    /**
     * Get a String representation of the value of this
     *
     * @return   The value
     */
    public String getValue()
    {
       return value;       
    }


    /**
     * Get the duration of this element
     *
     * @param beats  The beats in this element (whole=1, half=2, quarter=4)
     * @param dotted Whether this element is dotted
     */
    protected void setDuration(int beats, boolean dotted)
    {
        durationInMillis = wholeNoteInMillis / beats;
        if (dotted) durationInMillis *= 1.5;
    }
    

    /**
     * Set the String representation of this element
     *
     * @param value  The value
     */
    protected void setValue(String value)
    {
       this.value = value;       
    }
    
    
}
        

Lyric

javaexamples/oopbasics/musicmachine/Lyric.java

/**
 * A lyric in a song
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class Lyric extends AbstractLineElement
{
    
    /**
     * Explicit Value Constructor
     *
     * @param text   The text/word
     * @param beats  The number of beats (whole=1, half=2, quarter=4)
     * @param dotted Dotted or not
     */
    public Lyric(String text, int beats, boolean dotted)
    {
       setValue(text);
       setDuration(beats, dotted);       
    }
    

}
        

Note

javaexamples/oopbasics/musicmachine/Note.java

/**
 * A note in a song
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class Note extends AbstractLineElement
{
    private boolean   sharp;
    private char      pitch;


    /**
     * Default Constructor
     *
     * Constructs a whole note at middle C
     */
    public Note()
    {
        this('C', false, 0, 1, false);
    }




    /**
     * Explicit Value Constructor
     *
     * @param pitch    The pitch ('A','B','C','D','E','F', 'G' or 'R')
     * @param sharp    true for a sharp and false for a natural
     * @param octave   The octave (relative to middle C)
     * @param duration 1 for whole notes, 2 for half notes, etc...
     * @param dotted   Whether the note is dotted
     */
    public Note(char pitch,   boolean sharp, int octave, 
                int duration, boolean dotted)
    {
        int     durationInMillis, midiBase, midiNumber;

        // Store the pitch and duration
        this.pitch    = Character.toUpperCase(pitch);
        
        // Correct for possible "mistakes" (B# and E#)
        // (Alternatively, we could treat a B# as a C and an
        // E# as an F)
        if ((pitch == 'B') || (pitch == 'E')) this.sharp = false;
        else                                  this.sharp = sharp;

        // Calculate the MIDI value
        midiBase = 60;
        if      (pitch == 'A') midiNumber = midiBase +  9;
        else if (pitch == 'B') midiNumber = midiBase + 11;
        else if (pitch == 'C') midiNumber = midiBase +  0;
        else if (pitch == 'D') midiNumber = midiBase +  2;
        else if (pitch == 'E') midiNumber = midiBase +  4;
        else if (pitch == 'F') midiNumber = midiBase +  5;
        else if (pitch == 'G') midiNumber = midiBase +  7;
        else                   midiNumber = -1;             // Rest        

        if (this.sharp) midiNumber = midiNumber + 1;

        midiNumber = midiNumber + (octave * 12);

        setValue(""+midiNumber);
        setDuration(duration, dotted);        
    }

}
        

Presenter

javaexamples/oopbasics/musicmachine/Presenter.java

/**
 * Requirements of an object that can display the elements
 * in a Part
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public interface Presenter
{
    /**
     * Set the value to be used the next time this Presnter
     * is turned on 
     *
     * @param value   The value
     */
    public abstract void setValue(String value);
    

    /**
     * Turn this presenter off
     */
    public abstract void turnOff();
    

    /**
     * Turn this presenter on
     */
    public abstract void turnOn();
    


}
        

Console

javaexamples/oopbasics/musicmachine/Console.java

/**
 * An object that displays text on the console
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class Console implements Presenter
{
    private String       text;
    

    /**
     * Set the value to be used the next time this Presnter
     * is turned on (required by Presenter)
     *
     * In this case, it is the text to display
     *
     * @param value   The value
     */
    public void setValue(String value)
    {
       text = value;
       
    }
    
    
    /**
     * Turn this presenter off (required by Presenter)
     *
     * In this case, this method does nothing
     */
    public void turnOff()
    {
    }
    
    

    /**
     * Turn this presenter on (required by Presenter)
     *
     * In this case, this method outputs the value to
     * the console
     */
    public void turnOn()
    {
       System.out.println(text);
    }
    
    


}
        

InstrumentSynthesizer

javaexamples/oopbasics/musicmachine/InstrumentSynthesizer.java

import javax.sound.midi.*;


/**
 * An object that synthesizes the sounds made by an instrument
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class InstrumentSynthesizer implements Presenter
{
    int          midiNote;
    MidiChannel  channel;
    

    /**
     * Explicit Value Constructor
     *
     * @param channel   The MIDI channel on the synthesizer to use
     */
    public InstrumentSynthesizer(MidiChannel channel)
    {
       this.channel = channel;       
    }
    


    /**
     * Set the value to be used the next time this Presnter
     * is turned on (required by Presenter)
     *
     * In this case, it is a String representation of the
     * MIDI note value
     *
     * @param value   The value
     */
    public void setValue(String value)
    {
       midiNote = Integer.parseInt(value);
       
    }
    
    

    /**
     * Turn this presenter off (required by Presenter)
     *
     * In this case, this method turns the MIDI channel
     * off
     */
    public void turnOff()
    {
       channel.noteOff(midiNote);       
    }
    
    

    /**
     * Turn this presenter on (required by Presenter)
     *
     * In this case, this method turns the MIDI channel
     * on
     */
    public void turnOn()
    {
       channel.noteOn(midiNote, 127);       
    }
    
    


}
        

MetronomeListener

javaexamples/oopbasics/musicmachine/MetronomeListener.java

/**
 * Requirements of a MetronomeListener
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public interface MetronomeListener
{
    /**
     * Handle a "tick" of the Metronome
     *
     * @param metronome  The source of the "tick"
     */
    public abstract void handleTick(Metronome metronome);
}
        

Part

javaexamples/oopbasics/musicmachine/Part.java

import java.awt.event.*;
import java.util.*;

/**
 * A Part (i.e., a sequence of Note or Lyric objects) in a Score
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class Part  implements MetronomeListener
{
    private AbstractLineElement      element;
    private AbstractLineElement[]    elements;
    private int                      currentIndex, duration;
    private int                      elapsed, lastIndex;    
    private Presenter                presenter;


    /**
     * Explicit Value Constructor
     *
     * @param size  The number of elements in this Part
     */
    public Part(int size)
    {
       elements     = new AbstractLineElement[size];
       currentIndex = 0;       
       lastIndex    = 0;       
       duration     = 0;       

    }




    /**
     * Get an AbstractLineElement
     */
    public AbstractLineElement getElement(int i)
    {
       AbstractLineElement      element;
       
       element = null;
       if ((i >= 0) && (i < elements.length))
       {
          element = elements[i];          
       }
       

       return element;       
    }



    /**
     * Handle a "tick" of the Metronome (required by MetronomeListener)
     *
     * @param metronome  The source of the "tick"
     */
    public void handleTick(Metronome metronome)
    {
       elapsed += metronome.DELAY_IN_MILLIS;
       
       if (elapsed >= duration)
       {
          presenter.turnOff();
          
          element = getElement(currentIndex);
          currentIndex++;          

          if (element != null)
          {
             duration = element.getDurationInMillis();

             presenter.setValue(element.getValue());
             presenter.turnOn();
          }
          
          elapsed = 0;          
       }
    }
    




    /**
     * Set an AbstractLineElement
     *
     * @param i        The index
     * @param element  The element
     */
    public void setElement(int i, AbstractLineElement element)
    {
       if ((i >= 0) && (i < elements.length))
       {
          elements[i] = element;
       }
    }



    /**
     * Set the Presenter to use when "presenting" this
     * Part
     *
     * @param presenter   The Presenter to use
     */
    public void setPresenter(Presenter presenter)
    {
       this.presenter = presenter;
       
    }
    
}
        

Song

javaexamples/oopbasics/musicmachine/Song.java

import java.awt.event.*;

/**
 * A Song
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class Song implements MetronomeListener
{
    
    private Part[]           parts;
    private String           title;
    

    /**
     * Explicit Value Constructor
     *
     * @param numberOfParts  The number of Part objects in this Song
     */
    public Song(int numberOfParts)
    {
       parts = new Part[numberOfParts];       
    }
    

    /**
     * Set a Part
     *
     * @param i     The index
     * @param part  The Part
     */
    public void setPart(int i, Part part)
    {
       parts[i] = part;       
    }
    


    /**
     * Handle a "tick" of the Metronome (required by MetronomeListener)
     *
     * In this case, this method just delegates to the
     * component Part objects
     *
     * @param metronome  The source of the "tick"
     */
    public void handleTick(Metronome metronome)
    {
       for (int i=0; i<parts.length; i++)
       {
          if (parts[i] != null) parts[i].handleTick(metronome);          
       }
    }
    
}
        

• The Design Process:
  • Could have been improved by differentiating between conceptual models (for analysis) and class models (for engineering design)
• The Design Itself:
  • Could have been improved using design patterns, most notably the Model-View-Controller Pattern