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...

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

WhatsApp 0.2.1880 - Desktop client for W...
WhatsApp is the desktop client for WhatsApp Messenger, a cross-platform mobile messaging app which allows you to exchange messages without having to pay for SMS. WhatsApp Messenger is available for... Read more
NeoFinder 6.9.3 - Catalog your external...
NeoFinder (formerly CDFinder) rapidly organizes your data, either on external or internal disks, or any other volumes. It catalogs all your data, so you stay in control of your data archive or disk... Read more
Amadeus Pro 2.3.1 - Multitrack sound rec...
Amadeus Pro lets you use your Mac computer for any audio-related task, such as live audio recording, digitizing tapes and records, converting between a variety of sound formats, etc. Thanks to its... Read more
Yasu 4.0.0 β - System maintenance app; p...
Yasu was created with System Administrators who service large groups of workstations in mind, Yasu (Yet Another System Utility) was made to do a specific group of maintenance tasks quickly within a... Read more
Hazel 4.0.6 - Create rules for organizin...
Hazel is your personal housekeeper, organizing and cleaning folders based on rules you define. Hazel can also manage your trash and uninstall your applications. Organize your files using a familiar... Read more
EtreCheck 3.0.5 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
Skype 7.37.0.178 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
Yasu 4.0.0 β - System maintenance app; p...
Yasu was created with System Administrators who service large groups of workstations in mind, Yasu (Yet Another System Utility) was made to do a specific group of maintenance tasks quickly within a... Read more
Skype 7.37.0.178 - Voice-over-internet p...
Skype allows you to talk to friends, family and co-workers across the Internet without the inconvenience of long distance telephone charges. Using peer-to-peer data transmission technology, Skype... Read more
EtreCheck 3.0.5 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more

How to get past Vulture Island's tr...
Vulture Island is a colorful and quirky mish-mash of platforming and puzzles. It’s creative and fresh, but sometimes the game can throw a curveball at you, leaving you stuck as to how you should progress. These tips will help you explore smoothly... | Read more »
The new Clash of Kings is just for Weste...
If you’ve played the original Clash of Kings, you’ll probably recognise the city building, alliance forging and strategic battles in Clash of Kings: The West. What sets this version apart is that it’s tailor made for a Western audience and the... | Read more »
Frost - Survival card game (Games)
Frost - Survival card game 1.12.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.12.1 (iTunes) Description: *Warning: the game will work on iPhone 5C and above and iPad Pro / 4. Other devices are not supported* | Read more »
How to build and care for your team in D...
Before you hit the trail and become a dog sledding legend, there’s actually a fair bit of prep work to be done. In Dog Sled Saga, you’re not only racing, you’re also building and caring for a team of furry friends. There’s a lot to consider—... | Read more »
How to win every race in Dog Sled Saga
If I had to guess, I’d say Dog Sled Saga is the most adorable racing game on the App Store right now. It’s a dog sled racing sim full of adorable, loyal puppies. Just look at those fluffy little tails wagging. Behind that cute, pixelated facade is... | Read more »
Let the war games commence in Gunship Ba...
Buzz Lightyear famously said, “This isn’t flying, this is falling – with style!” In the case of Gunship Battle: Second War, though, this really is flying - with style! The flight simulator app from Joycity puts you in control of 20 faithfully... | Read more »
How to get a high score in Fired Up
Fired Up is Noodlecake Games’ high score chasing, firefighting adventure. You take control of a wayward firefighter who propels himself up the side of a highrise with blasts of water. Sound silly? It is. It’s also pretty difficult. You can’t... | Read more »
NBA 2K17 (Games)
NBA 2K17 1.0 Device: iOS iPhone Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: Following the record-breaking launch of NBA 2K16, the NBA 2K franchise continues to stake its claim as the most authentic sports video... | Read more »
Dog Sled Saga (Games)
Dog Sled Saga 1.0.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0.1 (iTunes) Description: A game by Dan + Lisa As a rookie musher, foster a dogsledding team whose skills will grow if they're treated right. Week by... | Read more »
60 Seconds! Atomic Adventure (Games)
60 Seconds! Atomic Adventure 1.2 Device: iOS Universal Category: Games Price: $2.99, Version: 1.2 (iTunes) Description: 60 Seconds! is a dark comedy atomic adventure of scavenge and survival. Collect supplies and rescue your family... | Read more »

Price Scanner via MacPrices.net

21-inch iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ iMacs on sale for up to $120 off MSRP including free shipping plus NY sales tax only: - 21″ 3.1GHz iMac 4K: $1379 $120 off MSRP - 21″ 2.8GHz iMac: $1199.99 $100 off MSRP - 21″ 1... Read more
13-inch 2.7GHz/256GB Retina MacBook Pro on sa...
Amazon.com has the 13″ 2.7GHz/256GB Retina Apple MacBook Pro on sale for $151 off MSRP including free shipping: - 13″ 2.7GHz/256GB Retina MacBook Pro (sku MF840LL/A): $1348 $151 off MSRP Read more
Apple TVs on sale for up to $50 off MSRP
Best Buy has 32GB and 64GB Apple TVs on sale for $40-$50 off MSRP on their online store. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-store... Read more
Apple refurbished 13-inch Retina MacBook Pros...
Apple has Certified Refurbished 13″ Retina MacBook Pros available for up to $270 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free: - 13″ 2.7GHz... Read more
Duplicate Sweeper Free On Mac App Store For O...
To celebrate the launch of Apple’s latest macOS Sierra, Stafford, United Kingdom based Wide Angle Software has announced that its duplicate file finder software, Duplicate Sweeper, is now available... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina Apple MacBook Pros on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY tax only: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1174.99 $125 off MSRP - 13... Read more
Evidence Surfaces Pointing To New A10X Chip F...
Citing a job description for a Project Lead position at Apple’s Austin, Texas engineering labs, Motley Fool’s Ashraf Eassa deduces that development is progressing well on Apple’s next-generation in-... Read more
Check Print’R for macOS Allows Anyone to Easi...
Delaware-based Match Software has announced the release and immediate availability of Check Print’R 3.21, an important update to their easy-to-use check printing application for macOS. Check Print’R... Read more
Apple refurbished 11-inch MacBook Airs availa...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models), available for up to $170 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Apple refurbished 15-inch Retina MacBook Pros...
Apple has Certified Refurbished 2015 15″ Retina MacBook Pros available for up to $380 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free: - 15″ 2... Read more

Jobs Board

Sr. *Apple* Mac Engineer - Net2Source Inc....
…staffing, training and technology. We have following position open with our client. Sr. Apple Mac Engineer6+ Months CTH Start date : 19th Sept Travelling Job If Read more
*Apple* Retail - Multiple Positions-Norfolk,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
Lead *Apple* Solutions Consultant - Apple (...
# Lead Apple Solutions Consultant Job Number: 51829230 Detroit, Michigan, United States Posted: Sep. 19, 2016 Weekly Hours: 40.00 **Job Summary** The Lead ASC is an Read more
US- *Apple* Store Leader Program - Apple (Un...
…Summary Learn and grow as you explore the art of leadership at the Apple Store. You'll master our retail business inside and out through training, hands-on Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.