CS535 Object-Oriented Programming & Design
Fall Semester, 1996
Doc 23 AWT Buttons, Model-View

1. References
2. Very Short Overview of AWT Parts
   1. Buttons
      1. Handling Button Events
      2. Custom Buttons
3. Separating the GUI from the Program
   1. Model-View
   2. Observable and Observer

Doc 23 AWT Buttons, Model-View Slide # 1

Doc 23 AWT Buttons, Model-View Slide # 2

When a user activates one of these controls -- by clicking a button for example -- it posts an event (ACTION_EVENT). An object that contains the control can react to the event by implementing the action() or handleEvent() method.

Ways of Getting User Input

Doc 23 AWT Buttons, Model-View Slide # 3

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Doc 23 AWT Buttons, Model-View Slide # 4

Dialog, FileDialog, and Frame are subclasses

Provide windows to contain components

Group components within an area of an existing window

Doc 23 AWT Buttons, Model-View Slide # 5

Doc 23 AWT Buttons, Model-View Slide # 6

import java.awt.*;

class  ButtonExample  extends Frame
   {   
   public ButtonExample( int  widthInPixels, int heightInPixels )
      {
      setTitle( "Button Example" );
      resize( widthInPixels, heightInPixels );

      setLayout( new FlowLayout() );
      add( new Button( "Red" ) );
      add( new Button( "Blue" ) );
      
      show();
      }
   }

class TestButton
   {
   public  static  void  main( String  args[] )
      {
      new  ButtonExample(200, 50);
      }
   }

Doc 23 AWT Buttons, Model-View Slide # 7

PC, Mac, Unix, PDA, toasters, TVs

Doc 23 AWT Buttons, Model-View Slide # 8

import java.awt.*;

class  ButtonExample  extends Frame
   {   
   public ButtonExample( int  widthInPixels, int heightInPixels )
      {
      setTitle( "Button Example" );
      resize( widthInPixels, heightInPixels );
      setLayout( new FlowLayout() );
      add( new Button( "Red" ) );
      add( new Button( "Blue" ) );
      
      show();
      }

   public boolean action( Event processNow, Object argument )
      {
      if ( buttonPressed.equals( "Red" ) )
         setBackground( Color.red );
      else if ( buttonPressed.equals( "Blue" ) ) 
         setBackground( Color.blue );
      else return false;
      
      repaint();      // Show effect of color change
      return true;
      }
      
   public  static  void  main( String  args[] ){
      ButtonExample  window = new  ButtonExample(200, 50);
      }
   }

---

Doc 23 AWT Buttons, Model-View Slide # 9

class  ButtonExample  extends Frame
   {
   Button red = new Button( "Red" );
   Button blue = new Button( "Blue" );
      
   public ButtonExample( int  widthInPixels, int heightInPixels )
      {
      setTitle( "Button Example" );
      resize( widthInPixels, heightInPixels );
      setLayout( new FlowLayout() );
      add( red );
      add( blue );
      show();
      }

   public boolean action( Event processNow, Object argument )
      {
      if ( processNow.target == red )
         setBackground( Color.red );
      else if (  processNow.target == blue ) 
         setBackground( Color.blue );
      else return false;
      
      repaint();      // Show effect of color change
      return true;
      }
   }

Doc 23 AWT Buttons, Model-View Slide # 10

import java.awt.*;

class  PaintRepaint  extends Frame{
   int drawPoint = 10;
   Button move = new Button( "Move" );
         
   public PaintRepaint( int  widthInPixels, int heightInPixels ) {
      setTitle( "PaintRepaint Example" );
      resize( widthInPixels, heightInPixels );
      setLayout( new FlowLayout() );
      add( move );   
      show();
   }

   public  void  paint(  Graphics  display  ){
      display.drawString(  "Hello World", drawPoint, drawPoint  );
   }
      
   public boolean action( Event processNow, Object argument ) {
      if ( processNow.target == move )
         drawPoint = drawPoint + 15;
      else return false;
      
      repaint();      // Show effect moving the text
      return true;
      }
      
   public  static  void  main( String  args[] ) {
      new  PaintRepaint(250, 150);
      }
   }
Doc 23 AWT Buttons, Model-View Slide # 11

---

Doc 23 AWT Buttons, Model-View Slide # 12

   public boolean action( Event processNow, Object argument )
      {
      if ( processNow.target == red )
         setBackground( Color.red );
      else if ( processNow.target == blue ) 
         setBackground( Color.blue );
      else if ( processNow.target ==  ok ) 
         //code here
      else if ( processNow.target == quit )
         //code here
      else if ( processNow.target ==  pause )
         //code here
      else if ( processNow.target ==  start )
         //code here
      else if ( processNow.target ==  green )


      etc.
Doc 23 AWT Buttons, Model-View Slide # 13

class ColorButton extends Button
   {
   Frame windowToColor;
   Color paintColor;
   
   public ColorButton( String buttonName, Color colorToUse, 
                     Frame toColor )
      {
      super( buttonName );
      paintColor = colorToUse;
      windowToColor = toColor;
      }
      
   public boolean action( Event processNow, Object argument )
      {
      windowToColor.setBackground( paintColor );
      windowToColor.repaint();
      return true;
      }
   }

Doc 23 AWT Buttons, Model-View Slide # 14

import java.awt.*;

class  ButtonExample  extends Frame
   {   
   public ButtonExample( int  widthInPixels, int heightInPixels )
      {
      setTitle( "Button Example" );
      resize( widthInPixels, heightInPixels );
      setLayout( new FlowLayout() );

      add( new ColorButton( "Red", Color.red, this ) );
      add( new ColorButton( "Blue" , Color.blue, this) );
      add( new ColorButton( "Green" , Color.green, this) );
      add( new ColorButton( "Yellow" , Color.yellow, this) );
      add( new ColorButton( "Dark Gray" , Color.darkGray, this) );

      show();
      }
   }
   
class TestButton
   {   
   public  static  void  main( String  args[] )
      {
      new  ButtonExample(200, 200);
      new  ButtonExample(200, 200);
      }
   }
Doc 23 AWT Buttons, Model-View Slide # 15

Doc 23 AWT Buttons, Model-View Slide # 16

can increase

can decrease

can be reset to zero

Doc 23 AWT Buttons, Model-View Slide # 17

class  BadCounterExample  extends Frame  {
   Button increase = new Button( "Increase" );
   Button decrease = new Button( "Decrease" );
   Button reset = new Button( "Reset" );
   int count = 0;
      
   public BadCounterExample( int  width, int height ) {
      setTitle( "Button Example" );
      resize( width, height );
      setLayout( new FlowLayout() );
      add( increase );
      add( decrease );
      add( reset );
      show();
   }

   public boolean action( Event processNow, Object argument ) {
      if ( processNow.target == increase )         count++;
      else if (  processNow.target == decrease )    count--;
      else if (  processNow.target == reset )       count = 0;
      else                               return false;
      
      repaint();
      return true;
   }

   public  void  paint(  Graphics  display  )  {
      display.drawString(  "The count is " + count , 50, 50  );
   }

   public  static  void  main( String  args[] ){
      new  BadCounterExample( 200,  100 );
   }
}
Doc 23 AWT Buttons, Model-View Slide # 18

Doc 23 AWT Buttons, Model-View Slide # 19

Doc 23 AWT Buttons, Model-View Slide # 20

Give flexibility in combining new views to a model

Allows multiple views on the same model

---

Doc 23 AWT Buttons, Model-View Slide # 21

class Counter
   {
   private int count = 0;
   
   public void increase() 
      { 
      count++; 
      }

   public void decrease() 
      { 
      count--; 
      }

   public void reset() 
      { 
      count = 0; 
      }
      
   public int value()
      { 
      return count; 
      }

   public String toString() 
      { 
      return String.valueOf( count ); 
      }
   }
Doc 23 AWT Buttons, Model-View Slide # 22

class  CounterExample  extends Frame
   {
   Button increase = new Button( "Increase" );
   Button decrease = new Button( "Decrease" );
   Counter count;

   public CounterExample( int width, int height, Counter outside )
      {
      setTitle( "Model View Button" );
      resize( width, height );
      setLayout( new FlowLayout() );
      add( increase );
      add( decrease );
      
      count = outside ;
      show();
      }

   public boolean action( Event processNow, Object buttonPressed )
      {
      if ( processNow.target == increase )
         count.increase();
      else if (  processNow.target == decrease )
         count.decrease();
      else 
         return false;
      
      repaint();
      return true;
      }

   public  void  paint(  Graphics  display  )  
      {
      display.drawString(  "The count is " + count , 50, 50  );
      }
   }
Doc 23 AWT Buttons, Model-View Slide # 23

class ButtonTest
   {
   public  static  void  main( String  args[] )
      {
      Counter test = new Counter();
      new  CounterExample( 200,  100, test );
      test = new Counter();
      new  CounterExample( 200,  100, test );
      }
   }

Doc 23 AWT Buttons, Model-View Slide # 24

class ButtonTest
   {
   public  static  void  main( String  args[] )
      {
      Counter test = new Counter();
      new  CounterExample( 200,  100, test );
      new  CounterExample( 200,  100, test );
      }
   }

Doc 23 AWT Buttons, Model-View Slide # 25

Observable object may have any number of Observers

Whenever the Observable instance changes,

it notifies all of its observers

Notification is done by calling the update() method on all observers.

When implemented, this interface allows all classes to be observable by instances of class Observer

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Doc 23 AWT Buttons, Model-View Slide # 26

java.util.Observable Methods

Adds an observer to the observer list.

Clears an observable change.

Counts the number of observers.

Deletes an observer from the observer list.

Deletes observers from the observer list.

Returns a true boolean if an observable change has occurred.

Notifies all observers if an observable change occurs.

Notifies all observers of the specified observable change which occurred.

Sets a flag to note an observable change.

Called when observers in the observable list need to be updated

Doc 23 AWT Buttons, Model-View Slide # 27

class SimpleCounter extends Observable{
   public int count = 0;
   
   public void increase() { 
      count++; 
      setChanged();
      notifyObservers(); 
   }
}
   
class SimpleObserver implements Observer  {
   String id;
   public SimpleObserver( String id ) {
      this.id = id ;
   }

   public void update( Observable sender, Object message ) {
      System.out.println( "From " + id + " New value " + 
         ((SimpleCounter) sender).count );
   }
}
   
class ObserveTest {
   public  static  void  main( String  args[] ) {
      SimpleCounter test = new SimpleCounter();
      SimpleObserver a = new SimpleObserver( "a" );
      test.addObserver( a);
      test.addObserver( new SimpleObserver( "b" ) );
      test.increase();
      test.addObserver( new SimpleObserver( "c" ) );
      test.increase();
      }
   }

Doc 23 AWT Buttons, Model-View Slide # 28

class ObserveTest {
   public  static  void  main( String  args[] ) {
      SimpleCounter test = new SimpleCounter();
      SimpleObserver a = new SimpleObserver( "a" );
      test.addObserver( a);
      test.addObserver( new SimpleObserver( "b" ) );
      test.increase();
      test.addObserver( new SimpleObserver( "c" ) );
      test.increase();
      }
   }