TweetFollow Us on Twitter

Feb 97 Getting Started

Volume Number: 13 (1997)
Issue Number: 2
Column Tag: Getting Started

The ShapeWorld Applet

By Dave Mark

A few months ago I promised an applet that did double-buffered animation. When I started work on the sample applet, I realized that I was definitely jumping the gun and there was still a lot of ground to cover to get to double-buffering. Since then, I've explored the AWT event-handling mechanism, as well as the various shape drawing routines in the Graphics class.

This month I am going to bring these concepts (and a few new ones) together into an applet called ShapeWorld. This month's version of ShapeWorld (I'll extend it next month) randomly scatters some rectangles into a Canvas, then responds to mouse clicks by selecting and deselecting the rectangles. As you'll see next month, ShapeWorld was designed to be extended. For now, let's get the first version up and running.

The ShapeWorld Project

Launch the CodeWarrior IDE and create a new project named ShapeWorld.µ using the Java applet stationery. Create a new source file named ShapeWorld.java and add it to the project. Here's the ShapeWorld.java source code:

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

abstract class Shape
{
 booleanhighlighted;
 ShapeCanvasshapeCanvas;
 int    shapeX, shapeY, shapeWidth, shapeHeight;
 RectangleboundsRect;
 Shape( ShapeCanvas canv, int x, int y,
 int width, int height )
 {
 shapeCanvas = canv;
 highlighted = false;
 
 shapeX = x;
 shapeY = y;
 shapeWidth = width;
 shapeHeight = height;
 boundsRect = new Rectangle( x, y, width, height );
 }
 
 abstract public void draw( Graphics g );
 
 public void setHighlight( boolean newHighlight )
 {
 highlighted = newHighlight;
 }
 
 public boolean isHighlighted()
 {
 return highlighted;
 }
 
 public boolean isPointInShape( int x, int y )
 {
 return boundsRect.inside( x, y );
 }
}

class RectShape extends Shape
{
 RectShape( ShapeCanvas canv, int x, int y,
 int width, int height )
 {
 super( canv, x, y, width, height );
 }
 
 public void draw( Graphics g )
 {
 if ( isHighlighted() )
 {
 g.setColor( Color.black );
 g.fillRect( shapeX, shapeY, shapeWidth, shapeHeight );
 g.setColor( Color.red );
 g.fillRect( shapeX+2, shapeY+2,
 shapeWidth-4, shapeHeight-4 );
 }
 else
 {
 g.setColor( Color.red );
 g.fillRect( shapeX, shapeY, shapeWidth, shapeHeight );
 }
 }
}

class ShapeCanvas extends Canvas
{
 Vector shapes;
 Shape  curShape;
 
 ShapeCanvas( int width, int height )
 {
 shapes = new Vector();
 curShape = null;
 
 setBackground( Color.yellow );
 
 resize( width, height );
 }
 
 public void addShape( Shape newShape )
 {
 shapes.addElement( newShape );
 }
 
 public void paint( Graphics g )
 {
 for ( Enumeration e = shapes.elements(); 
 e.hasMoreElements(); )
 {
 Shape s = (Shape)e.nextElement();
 s.draw( g );
 }
 }
 
 public Shape findInShapeList( int x, int y )
 {
 for ( Enumeration e = shapes.elements(); 
 e.hasMoreElements(); )
 {
 Shape s = (Shape)e.nextElement();
 
 if ( s.isPointInShape( x, y ) )
 {
 s.setHighlight( ! s.isHighlighted() );
 s.draw( getGraphics() );

 return s;
 }
 }
 
 return null;
 }
 
 public void update (Graphics g)
 {
   paint(g);
 }
 
 public boolean mouseDown( Event e, int x, int y )
 {
 curShape = findInShapeList( x, y );
 
 return true;
 }
}

public class ShapeWorld extends java.applet.Applet
{
 ShapeCanvassCanvas;
 final intshapeWidth = 20;
 final intshapeHeight = 20;
 
 public void init()
 {
 int    x, y;
 
 sCanvas = new ShapeCanvas( 440, 290 );
 add( sCanvas );
 
 Random ran = new Random();
 Rectangle b = sCanvas.bounds();
 
 for ( int i=1; i<=10; i++ )
 {
 x = b.x + (int)((float)(b.width) * ran.nextFloat() );
 if ( x > b.x + b.width - shapeWidth )
 x -= shapeWidth;
 
 y = b.y + (int)((float)(b.height) * ran.nextFloat() );
 if ( y > b.y + b.height - shapeHeight )
 y -= shapeHeight;
 
 RectShape r = new RectShape( sCanvas, x, y, 
 shapeWidth, shapeHeight );
 sCanvas.addShape( r );
 }
 }
}

Save your typing, then create a new source code file named ShapeWorld.html and add it to the project. Here's the html:

<title>ShapeWorld</title>
<hr>
<applet codebase="ShapeWorld Classes" code="ShapeWorld.class" width=500 
height=300>
</applet>
<hr>
<a href="ShapeWorld.java">The source.</a>

Running the ShapeWorld Applet

Once your source and html are entered and saved, run the ShapeWorld applet. Figure 1 shows my ShapeWorld applet running in the Metrowerks Java applet runner. The ten shapes all appear in red on a Canvas with a background color of yellow. The shapes are randomly distributed throughout the Canvas.

Figure 1. The ShapeWorld applet with no shapes selected.

Figure 2 shows what happens when I click the mouse inside a shape. In this case, I've selected six of the ten shapes. A two pixel border is used to mark a shape as selected.

Figure 2. The ShapeWorld applet with six shapes selected.

The ShapeWorld Source

ShapeWorld creates four classes. ShapeWorld is the main entry point and extends the java.applet.Applet class. The ShapeCanvas class implements the Canvas. The Shape class is an abstract class which means that I won't be creating any Shape objects. The RectShape class extends the Shape class and is used to create the ten shapes you see in the ShapeWorld Canvas.

As you look through the Shape class, remember that all the variables and functions will be inherited by any classes that extend Shape. highlighted is set to true if the shape is selected, false otherwise. shapeCanvas is the enclosing Canvas. shapeX, shapeY, shapeWidth, and shapeHeight define the boundries of this Shape. boundsRect does the exact same thing, but stores this same info in a Rectangle instead of in individual variables. Why the duplication? With both forms available, I don't have to spend time converting from one form to the other. This might seem like a frivolous waste of memory, but when we are stepping through a large number of shapes, perhaps during a redraw cycle, the little time we save can make a difference.

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

abstract class Shape
{
 booleanhighlighted;
 ShapeCanvasshapeCanvas;
 int    shapeX, shapeY, shapeWidth, shapeHeight;
 RectangleboundsRect;
 

The Shape constructor initializes the Shape variables. The draw() function is declared abstract, which means it must be overridden by any class that extends Shape. Note that an abstract function doesn't have a function body. setHighlight() sets highlighted to a new value. isHighlighted() returns the value of highlighted. Finally, isPointInShape() takes advantage of the Rectangle classes' inside() function to tell you if the specified point is inside the Shape's bounding Rectangle.

 Shape( ShapeCanvas canv, int x, int y,
 int width, int height )
 {
 shapeCanvas = canv;
 highlighted = false;
 
 shapeX = x;
 shapeY = y;
 shapeWidth = width;
 shapeHeight = height;
 
 boundsRect = new Rectangle( x, y, width, height );
 }
 
 abstract public void draw( Graphics g );
 
 public void setHighlight( boolean newHighlight )
 {
 highlighted = newHighlight;
 }
 
 public boolean isHighlighted()
 {
 return highlighted;
 }
 
 public boolean isPointInShape( int x, int y )
 {
 return boundsRect.inside( x, y );
 }
}

RectShape extends the Shape class. The RectShape constructor just passes on its parameters to its superclass constructor, which is the Shape constructor. If the shape is selected, the draw() function draws a black rectangle, insets the rectangle by two pixels on each side, then draws a red rectangle. I could have used two calls to drawRect() to frame the black rectangle followed by a call to fillRect() to fill in the red, but this made the code easier to read.

class RectShape extends Shape
{
 RectShape( ShapeCanvas canv, int x, int y,
 int width, int height )
 {
 super( canv, x, y, width, height );
 }
 
 public void draw( Graphics g )
 {
 if ( isHighlighted() )
 {
 g.setColor( Color.black );
 g.fillRect( shapeX, shapeY, shapeWidth, shapeHeight );
 g.setColor( Color.red );
 g.fillRect( shapeX+2, shapeY+2,
 shapeWidth-4, shapeHeight-4 );
 }
 else
 {
 g.setColor( Color.red );
 g.fillRect( shapeX, shapeY, shapeWidth, shapeHeight );
 }
 }
}

The ShapeCanvas class is my main drawing area. The shapes variable is of the java.util.Vector class. A Vector implements a growable array of objects. I can access the objects via random access (using an integer index) or by stepping through the list. Since I want to tie a list of shapes to my Canvas, a Vector is a natural structure in which to store references to the Shapes. Spend some time reading the java.util.Vector doc to truly appreciate the value of the Vector. In addition, you should read about the Enumeration interface (on the java.util page) that the Vector class implements. The Enumeration interface allows you to step through your Vector using the functions hasMoreElements() and nextElement().

class ShapeCanvas extends Canvas
{
 Vector shapes;
 Shape  curShape;

The ShapeCanvas() constructor creates a new Vector and sets curShape to null. I won't make use of curShape this month, but I will use it next month to keep track of the last selected Shape. The constructor also sets the background color and changes the Canvas' size.

 ShapeCanvas( int width, int height )
 {
 shapes = new Vector();
 curShape = null;
 
 setBackground( Color.yellow );
 
 resize( width, height );
 }

addShape() adds a shape to the Vector. paint() steps through the shapes Vector, retrieving the current Shape and calling its draw() method. This method of stepping through a Vector is extremely useful. Note that nextElement() returns an Object, so I needed to cast the returned value to Shape. By retrieving a Shape instead of a specific derived class such as RectShape(), I can use this code to draw any Shapes stored in the list, no matter the type, as long as each shape is derived from Shape.

 public void addShape( Shape newShape )
 {
 shapes.addElement( newShape );
 }
 
 public void paint( Graphics g )
 {
 for ( Enumeration e = shapes.elements(); 
 e.hasMoreElements(); )
 {
 Shape s = (Shape)e.nextElement();
 s.draw( g );
 }
 }

findInShapeList() also steps through the shapes Vector. In each case, I call each Shape's isPointInShape() function to see if the specified point is in the current Shape. If the point was in the Shape, I flip highlighted and redraw the Shape (since it is now selected.)

 public Shape findInShapeList( int x, int y )
 {
 for ( Enumeration e = shapes.elements(); 
 e.hasMoreElements(); )
 {
 Shape s = (Shape)e.nextElement();
 
 if ( s.isPointInShape( x, y ) )
 {
 s.setHighlight( ! s.isHighlighted() );
 s.draw( getGraphics() );

 return s;
 }
 }
 
 return null;
 }

The update() function calls paint(). The default update() (inherited from the Component class) erases the area to be updated and then calls paint(). By calling paint() without the erase, I avoid an annoying flicker. This trick is well worth remembering. To truly understand what it does, comment out the entire update() method (not just the call to paint() which will prevent drawing from occuring at all!!!)

 public void update (Graphics g)
 {
   paint(g);
 }

The mouseDown() function gets called when I click the mouse in the Canvas. At the moment, I don't do anything interesting with the Shape returned by findInShapeList(), but I will next month.

 public boolean mouseDown( Event e, int x, int y )
 {
 curShape = findInShapeList( x, y );
 
 return true;
 }
}

The last thing I want to point out this month is the use of the Random class. ShapeWorld creates 10 new RectShapes (remember, you can't actually create a Shape since you can't create an instance of an abstract class) using the random values returned by Random(). Random is described on the page java.util.Random. Be sure to check out that page of documentation, as it describes a variety of random number distributions and returned types.

public class ShapeWorld extends java.applet.Applet
{
 ShapeCanvassCanvas;
 final intshapeWidth = 20;
 final intshapeHeight = 20;
 
 public void init()
 {
 int    x, y;
 
 sCanvas = new ShapeCanvas( 440, 290 );
 add( sCanvas );
 Random ran = new Random();
 Rectangle b = sCanvas.bounds();
 
 for ( int i=1; i<=10; i++ )
 {
 x = b.x + (int)((float)(b.width) * ran.nextFloat() );
 if ( x > b.x + b.width - shapeWidth )
 x -= shapeWidth;
 
 y = b.y + (int)((float)(b.height) * ran.nextFloat() );
 if ( y > b.y + b.height - shapeHeight )
 y -= shapeHeight;
 
 RectShape r = new RectShape( sCanvas, x, y, 
 shapeWidth, shapeHeight );
 sCanvas.addShape( r );
 }
 }
}

Till Next Month...

As promised, next month I'll add some new functionality to ShapeWorld. Before you peek at next month's column, try your hand at adding a new Shape subclass to ShapeWorld. Experiment. Read the doc. I'll see you then...

 
AAPL
$107.80
Apple Inc.
+0.82
MSFT
$46.82
Microsoft Corpora
+0.77
GOOG
$558.34
Google Inc.
+8.03

MacTech Search:
Community Search:

Software Updates via MacUpdate

Vitamin-R 2.20b1 - Personal productivity...
Vitamin-R creates the optimal conditions for your brain to work at its best by structuring your work into short bursts of distraction-free, highly focused activity alternating with opportunities for... Read more
Dropbox 2.10.44 - Cloud synchronization...
Dropbox is an application that creates a special Finder folder that automatically syncs online and between your computers. It allows you to both backup files and keep them up-to-date between systems... Read more
Sandvox 2.9.2 - Easily build eye-catchin...
Sandvox is for Mac users who want to create a professional looking website quickly and easily. With Sandvox, you don't need to be a Web genius to build a stylish, feature-rich, standards-compliant... Read more
Cocktail 8.0.1 - General maintenance and...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
LibreOffice 4.3.3.2 - Free Open Source o...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
VMware Fusion 7.0.1 - Run Windows apps a...
VMware Fusion allows you to create a Virtual Machine on your Mac and run Windows (including Windows 8.1) and Windows software on your Mac. Run your favorite Windows applications alongside Mac... Read more
OneNote 15.3.2 - Free digital notebook f...
OneNote is your very own digital notebook. With OneNote, you can capture that flash of genius, that moment of inspiration, or that list of errands that's too important to forget. Whether you're at... Read more
Audio Hijack Pro 2.11.4 - Record and enh...
Audio Hijack Pro drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio with Audio Hijack... Read more
Iridient Developer 3.0.0 beta 3 - Powerf...
Iridient Developer (was RAW Developer) is a powerful image conversion application designed specifically for OS X. Iridient Developer gives advanced photographers total control over every aspect of... Read more
TextWrangler 4.5.11 - Free general purpo...
TextWrangler is the powerful general purpose text editor, and Unix and server administrator's tool. Oh, and also, like the best things in life, it's free. TextWrangler is the "little brother" to... Read more

Latest Forum Discussions

See All

Monster Flash Review
Monster Flash Review By Jordan Minor on October 31st, 2014 Our Rating: :: ALONE IN THE DARKUniversal App - Designed for iPhone and iPad Solid shooting and a surprising amount of spooky tension make Monster Flash a great portable... | Read more »
Retry Review
Retry Review By Rob Thomas on October 31st, 2014 Our Rating: :: SOARING HIGHUniversal App - Designed for iPhone and iPad Flappy who? Let Retry wash all those bad bird-related memories away on a cool retro-flavored flight… right... | Read more »
Dementia: Book of the Dead Review
Dementia: Book of the Dead Review By Lee Hamlet on October 31st, 2014 Our Rating: :: A TOUGH READUniversal App - Designed for iPhone and iPad A witch hunter is sent after a demonic book in the spooky but short-lived Dementia: Book... | Read more »
Card Dungeon, the Semi-Board Game Roguel...
Card Dungeon, the Semi-Board Game Roguelike, Has Been Renovated Posted by Jessica Fisher on October 31st, 2014 [ permalink ] | Read more »
Logitech Protection + Power iPhone5/5S C...
Made by: Logitech Price: $99.99 Hardware/iOS Integration Rating: 3 out of 5 stars Usability Rating: 0.5 out of 5 stars Reuse Value Rating: 0.75 out of 5 stars Build Quality Rating: 0.75 out of 5 stars Overall Rating: 1.25 out of 5 stars | Read more »
This Is Not a Test Goes Free, Permanentl...
This Is Not a Test Goes Free, Permanently Posted by Jessica Fisher on October 31st, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Swap Heroes Review
Swap Heroes Review By Campbell Bird on October 31st, 2014 Our Rating: :: STRATEGIC SWAPPINGUniversal App - Designed for iPhone and iPad Rotate a cast of heroes to fend of waves of monsters in this difficult, puzzle rpg.   | Read more »
Night Sky Pro™ (Reference)
Night Sky Pro™ 3.0.1 Device: iOS Universal Category: Reference Price: $2.99, Version: 3.0.1 (iTunes) Description: Night Sky Pro™Wonder No More™ Night Sky Pro™ is the ultimate stargazing experience. From the creators of the original... | Read more »
Audio Defence : Zombie Arena (Games)
Audio Defence : Zombie Arena 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: A zombie shooter audio game. Made from gut-wrenching 3D binaural sound, for a new kind of weird immersion. You... | Read more »
RPG Asdivine Hearts (Games)
RPG Asdivine Hearts 1.1.0 Device: iOS Universal Category: Games Price: $3.99, Version: 1.1.0 (iTunes) Description: SPECIAL PRICE50% OFF (USD 7.99 -> USD 3.99)!!! Travel alongside four companions and a cat in the adventure of a... | Read more »

Price Scanner via MacPrices.net

Apple now offering refurbished 2014 13-inch R...
The Apple Store is now offering Apple Certified Refurbished 2014 13″ Retina MacBook Pros for up to $270 off the cost of new models. An Apple one-year warranty is included with each model, and... Read more
Apple Regains Momentum As Windows Stutters An...
The latest smartphone sales data from Kantar Worldpanel ComTech, for the three months to March 2014, shows Apple performing strongly in the first quarter of the year, with sales bouncing back in... Read more
Worldwide Smartphone Shipments Increase 25.2%...
New smartphone releases and an increased emphasis on emerging markets drove global smartphone shipments above 300 million units for the second consecutive quarter, according to preliminary data from... Read more
Apple now offering refurbished 2014 15-inch M...
The Apple Store is now offering Apple Certified Refurbished 2014 15″ Retina MacBook Pros for up to $400 off the cost of new models. An Apple one-year warranty is included with each model, and... Read more
Apple drops prices on refurbished 2013 Retina...
The Apple Store has dropped prices on 2013 Apple Certified Refurbished 13″ and 15″ Retina MacBook Pros, with Retina models now available starting at $999. Apple’s one-year warranty is standard, and... Read more
New 2.8GHz Mac mini on sale for $949, save $5...
Abt Electronics has the new 2.8GHz Mac mini in stock and on sale for $949.05 including free shipping. Their price is $50 off MSRP, and it’s the lowest price available for this model from any reseller... Read more
Sale! 3.7GHz Quad Core Mac Pro available for...
 B&H Photo has the 3.7GHz Quad Core Mac Pro on sale for $2649 including free shipping plus NY sales tax only. Their price is $350 off MSRP, and it’s the lowest price for this model from any... Read more
Mujjo Steps Up The Game With Refined Touchscr...
Netherlands based Mujjo have just launched their Refined Touchscreen Gloves, stepping up their game. The gloves feature a updated elegant design that takes these knitted gloves to the next level. A... Read more
Sale! Preorder the new 27-inch 5K iMac for $2...
 Abt Electronics has the new 27″ 3.5GHz 5K iMac on sale and available for preorder for $2374.05 including free shipping. Their price is $125 off MSRP, and it’s the lowest price available for this... Read more
Simplex Solutions Inc. Brings Secure Web Surf...
New York based Simplex Solutions Inc. has announced the release and immediate availability of Private Browser 1.0, its revolutionary new secure web browser developed for iPhone, iPad and iPod touch... Read more

Jobs Board

Position Opening at *Apple* - Apple (United...
**Job Summary** Every day, business customers come to the Apple Store to discover what powerful, easy-to-use Apple products can do for them. As a Business Leader, Read more
Sr. Manager, *Apple* Deployment Programs fo...
**Job Summary** Apple is seeking candidates for a new position on the Education Content and Technology team. iPad and Mac is in the hands of millions of teachers and Read more
*Apple* Solutions Consultant (ASC) - Apple I...
…important role that the ASC serves is that of providing an excellent Apple Customer Experience. Responsibilities include: * Promoting Apple products and solutions Read more
*Apple* Solutions Consultant (ASC) - Apple I...
…important role that the ASC serves is that of providing an excellent Apple Customer Experience. Responsibilities include: * Promoting Apple products and solutions Read more
*Apple* Solutions Consultant (ASC) - Apple I...
…important role that the ASC serves is that of providing an excellent Apple Customer Experience. Responsibilities include: * Promoting Apple products and solutions Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.