You are previewing Learning Java, 4th Edition.

Learning Java, 4th Edition

Cover of Learning Java, 4th Edition by Daniel Leuck... Published by O'Reilly Media, Inc.
  1. Learning Java
  2. Preface
    1. Who Should Read This Book
    2. New Developments
      1. New in This Edition (Java 6 and 7)
    3. Using This Book
    4. Online Resources
    5. Conventions Used in This Book
    6. Using Code Examples
    7. Safari® Books Online
    8. How to Contact Us
    9. Acknowledgments
  3. 1. A Modern Language
    1. Enter Java
      1. Java’s Origins
      2. Growing Up
    2. A Virtual Machine
    3. Java Compared with Other Languages
    4. Safety of Design
      1. Simplify, Simplify, Simplify...
      2. Type Safety and Method Binding
      3. Incremental Development
      4. Dynamic Memory Management
      5. Error Handling
      6. Threads
      7. Scalability
    5. Safety of Implementation
      1. The Verifier
      2. Class Loaders
      3. Security Managers
    6. Application and User-Level Security
    7. A Java Road Map
      1. The Past: Java 1.0–Java 1.6
      2. The Present: Java 7
      3. The Future
      4. Availability
  4. 2. A First Application
    1. Java Tools and Environment
    2. Configuring Eclipse and Creating a Project
      1. Importing the Learning Java Examples
    3. HelloJava
      1. Classes
      2. The main() Method
      3. Classes and Objects
      4. Variables and Class Types
      5. HelloComponent
      6. Inheritance
      7. The JComponent Class
      8. Relationships and Finger Pointing
      9. Package and Imports
      10. The paintComponent() Method
    4. HelloJava2: The Sequel
      1. Instance Variables
      2. Constructors
      3. Events
      4. The repaint() Method
      5. Interfaces
    5. HelloJava3: The Button Strikes!
      1. Method Overloading
      2. Components
      3. Containers
      4. Layout
      5. Subclassing and Subtypes
      6. More Events and Interfaces
      7. Color Commentary
      8. Static Members
      9. Arrays
      10. Our Color Methods
    6. HelloJava4: Netscape’s Revenge
      1. Threads
      2. The Thread Class
      3. The Runnable Interface
      4. Starting the Thread
      5. Running Code in the Thread
      6. Exceptions
      7. Synchronization
  5. 3. Tools of the Trade
    1. JDK Environment
    2. The Java VM
    3. Running Java Applications
      1. System Properties
    4. The Classpath
      1. javap
    5. The Java Compiler
    6. JAR Files
      1. File Compression
      2. The jar Utility
      3. The pack200 Utility
    7. Policy Files
      1. The Default Security Manager
      2. The policytool Utility
      3. Using a Policy File with the Default Security Manager
  6. 4. The Java Language
    1. Text Encoding
    2. Comments
      1. Javadoc Comments
    3. Types
      1. Primitive Types
      2. Reference Types
      3. A Word About Strings
    4. Statements and Expressions
      1. Statements
      2. Expressions
    5. Exceptions
      1. Exceptions and Error Classes
      2. Exception Handling
      3. Bubbling Up
      4. Stack Traces
      5. Checked and Unchecked Exceptions
      6. Throwing Exceptions
      7. try Creep
      8. The finally Clause
      9. Try with Resources
      10. Performance Issues
    6. Assertions
      1. Enabling and Disabling Assertions
      2. Using Assertions
    7. Arrays
      1. Array Types
      2. Array Creation and Initialization
      3. Using Arrays
      4. Anonymous Arrays
      5. Multidimensional Arrays
      6. Inside Arrays
  7. 5. Objects in Java
    1. Classes
      1. Accessing Fields and Methods
      2. Static Members
    2. Methods
      1. Local Variables
      2. Shadowing
      3. Static Methods
      4. Initializing Local Variables
      5. Argument Passing and References
      6. Wrappers for Primitive Types
      7. Autoboxing and Unboxing of Primitives
      8. Variable-Length Argument Lists
      9. Method Overloading
    3. Object Creation
      1. Constructors
      2. Working with Overloaded Constructors
      3. Static and Nonstatic Initializer Blocks
    4. Object Destruction
      1. Garbage Collection
      2. Finalization
      3. Weak and Soft References
    5. Enumerations
      1. Enum Values
      2. Customizing Enumerations
  8. 6. Relationships Among Classes
    1. Subclassing and Inheritance
      1. Shadowed Variables
      2. Overriding Methods
      3. Special References: this and super
      4. Casting
      5. Using Superclass Constructors
      6. Full Disclosure: Constructors and Initialization
      7. Abstract Methods and Classes
    2. Interfaces
      1. Interfaces as Callbacks
      2. Interface Variables
      3. Subinterfaces
    3. Packages and Compilation Units
      1. Compilation Units
      2. Package Names
      3. Class Visibility
      4. Importing Classes
    4. Visibility of Variables and Methods
      1. Basic Access Modifiers
      2. Subclasses and Visibility
      3. Interfaces and Visibility
    5. Arrays and the Class Hierarchy
      1. ArrayStoreException
    6. Inner Classes
      1. Inner Classes as Adapters
      2. Inner Classes Within Methods
  9. 7. Working with Objects and Classes
    1. The Object Class
      1. Equality and Equivalence
      2. Hashcodes
      3. Cloning Objects
    2. The Class Class
    3. Reflection
      1. Modifiers and Security
      2. Accessing Fields
      3. Accessing Methods
      4. Accessing Constructors
      5. What About Arrays?
      6. Accessing Generic Type Information
      7. Accessing Annotation Data
      8. Dynamic Interface Adapters
      9. What Is Reflection Good For?
    4. Annotations
      1. Using Annotations
      2. Standard Annotations
      3. The apt Tool
  10. 8. Generics
    1. Containers: Building a Better Mousetrap
      1. Can Containers Be Fixed?
    2. Enter Generics
      1. Talking About Types
    3. “There Is No Spoon”
      1. Erasure
      2. Raw Types
    4. Parameterized Type Relationships
      1. Why Isn’t a List<Date> a List<Object>?
    5. Casts
    6. Writing Generic Classes
      1. The Type Variable
      2. Subclassing Generics
      3. Exceptions and Generics
      4. Parameter Type Limitations
    7. Bounds
      1. Erasure and Bounds (Working with Legacy Code)
    8. Wildcards
      1. A Supertype of All Instantiations
      2. Bounded Wildcards
      3. Thinking Outside the Container
      4. Lower Bounds
      5. Reading, Writing, and Arithmetic
      6. <?>, <Object>, and the Raw Type
      7. Wildcard Type Relationships
    9. Generic Methods
      1. Generic Methods Introduced
      2. Type Inference from Arguments
      3. Type Inference from Assignment Context
      4. Explicit Type Invocation
      5. Wildcard Capture
      6. Wildcard Types Versus Generic Methods
    10. Arrays of Parameterized Types
      1. Using Array Types
      2. What Good Are Arrays of Generic Types?
      3. Wildcards in Array Types
    11. Case Study: The Enum Class
    12. Case Study: The sort() Method
    13. Conclusion
  11. 9. Threads
    1. Introducing Threads
      1. The Thread Class and the Runnable Interface
      2. Controlling Threads
      3. Death of a Thread
    2. Threading an Applet
      1. Issues Lurking
    3. Synchronization
      1. Serializing Access to Methods
      2. Accessing class and instance Variables from Multiple Threads
      3. The wait() and notify() Methods
      4. Passing Messages
      5. ThreadLocal Objects
    4. Scheduling and Priority
      1. Thread State
      2. Time-Slicing
      3. Priorities
      4. Yielding
    5. Thread Groups
      1. Working with ThreadGroups
      2. Uncaught Exceptions
    6. Thread Performance
      1. The Cost of Synchronization
      2. Thread Resource Consumption
    7. Concurrency Utilities
      1. Executors
      2. Locks
      3. Synchronization Constructs
      4. Atomic Operations
    8. Conclusion
  12. 10. Working with Text
    1. Text-Related APIs
    2. Strings
      1. Constructing Strings
      2. Strings from Things
      3. Comparing Strings
      4. Searching
      5. Editing
      6. String Method Summary
      7. StringBuilder and StringBuffer
    3. Internationalization
      1. The java.util.Locale Class
      2. Resource Bundles
    4. Parsing and Formatting Text
      1. Parsing Primitive Numbers
      2. Tokenizing Text
    5. Printf-Style Formatting
      1. Formatter
      2. The Format String
      3. String Conversions
      4. Primitive and Numeric Conversions
      5. Flags
      6. Miscellaneous
    6. Formatting with the java.text Package
      1. MessageFormat
    7. Regular Expressions
      1. Regex Notation
      2. The java.util.regex API
  13. 11. Core Utilities
    1. Math Utilities
      1. The java.lang.Math Class
      2. Big/Precise Numbers
      3. Floating-Point Components
      4. Random Numbers
    2. Dates and Times
      1. Working with Calendars
      2. Time Zones
      3. Parsing and Formatting with DateFormat
      4. Printf-Style Date and Time Formatting
    3. Timers
    4. Collections
      1. The Collection Interface
      2. Iterator
      3. Collection Types
      4. The Map Interface
      5. Collection Implementations
      6. Hash Codes and Key Values
      7. Synchronized and Unsynchronized Collections
      8. Read-Only and Read-Mostly Collections
      9. WeakHashMap
      10. EnumSet and EnumMap
      11. Sorting Collections
      12. A Thrilling Example
    5. Properties
      1. Loading and Storing
      2. System Properties
    6. The Preferences API
      1. Preferences for Classes
      2. Preferences Storage
      3. Change Notification
    7. The Logging API
      1. Overview
      2. Logging Levels
      3. A Simple Example
      4. Logging Setup Properties
      5. The Logger
      6. Performance
    8. Observers and Observables
  14. 12. Input/Output Facilities
    1. Streams
      1. Basic I/O
      2. Character Streams
      3. Stream Wrappers
      4. Pipes
      5. Streams from Strings and Back
      6. Implementing a Filter Stream
    2. File I/O
      1. The java.io.File Class
      2. File Streams
      3. RandomAccessFile
      4. Resource Paths
    3. The NIO File API
      1. FileSystem and Path
      2. NIO File Operations
      3. Directory Operations
      4. Watching Paths
    4. Serialization
      1. Initialization with readObject()
      2. SerialVersionUID
    5. Data Compression
      1. Archives and Compressed Data
      2. Decompressing Data
      3. Zip Archive As a Filesystem
    6. The NIO Package
      1. Asynchronous I/O
      2. Performance
      3. Mapped and Locked Files
      4. Channels
      5. Buffers
      6. Character Encoders and Decoders
      7. FileChannel
      8. Scalable I/O with NIO
  15. 13. Network Programming
    1. Sockets
      1. Clients and Servers
      2. author="pat” timestamp="20120926T110720-0500” comment="one of those sections I hate to get rid of but is less relevant in terms of the example... should probably find a more modern example...”The DateAtHost Client
      3. The TinyHttpd Server
      4. Socket Options
      5. Proxies and Firewalls
    2. Datagram Sockets
      1. author="pat” timestamp="20120926T141346-0500” comment="I actually rewrote this as a standalone client but then decided to leave it as an applet”The HeartBeat Applet
      2. InetAddress
    3. Simple Serialized Object Protocols
      1. A Simple Object-Based Server
    4. Remote Method Invocation
      1. Real-World Usage
      2. Remote and Nonremote Objects
      3. An RMI Example
      4. RMI and CORBA
    5. Scalable I/O with NIO
      1. Selectable Channels
      2. Using Select
      3. LargerHttpd
      4. Nonblocking Client-Side Operations
  16. 14. Programming for the Web
    1. Uniform Resource Locators (URLs)
    2. The URL Class
      1. Stream Data
      2. Getting the Content as an Object
      3. Managing Connections
      4. Handlers in Practice
      5. Useful Handler Frameworks
    3. Talking to Web Applications
      1. Using the GET Method
      2. Using the POST Method
      3. The HttpURLConnection
      4. SSL and Secure Web Communications
      5. URLs, URNs, and URIs
    4. Web Services
      1. XML-RPC
      2. WSDL
      3. The Tools
      4. The Weather Service Client
  17. 15. Web Applications and Web Services
    1. Web Application Technologies
      1. Page-Oriented Versus “Single Page” Applications
      2. JSPs
      3. XML and XSL
      4. Web Application Frameworks
      5. Google Web Toolkit
      6. HTML5, AJAX, and More...
    2. Java Web Applications
      1. The Servlet Lifecycle
      2. Servlets
      3. The HelloClient Servlet
      4. The Servlet Response
      5. Servlet Parameters
      6. The ShowParameters Servlet
      7. User Session Management
      8. The ShowSession Servlet
      9. The ShoppingCart Servlet
      10. Cookies
      11. The ServletContext API
      12. Asynchronous Servlets
    3. WAR Files and Deployment
      1. Configuration with web.xml and Annotations
      2. URL Pattern Mappings
      3. Deploying HelloClient
      4. Error and Index Pages
      5. Security and Authentication
      6. Protecting Resources with Roles
      7. Secure Data Transport
      8. Authenticating Users
      9. Procedural Authorization
    4. Servlet Filters
      1. A Simple Filter
      2. A Test Servlet
      3. Declaring and Mapping Filters
      4. Filtering the Servlet Request
      5. Filtering the Servlet Response
    5. Building WAR Files with Ant
      1. A Development-Oriented Directory Layout
      2. Deploying and Redeploying WARs with Ant
    6. Implementing Web Services
      1. Defining the Service
      2. Our Echo Service
      3. Using the Service
      4. Data Types
    7. Conclusion
  18. 16. Swing
    1. Components
      1. Peers and Look-and-Feel
      2. The MVC Framework
      3. Painting
      4. Enabling and Disabling Components
      5. Focus, Please
      6. Other Component Methods
      7. Layout Managers
      8. Insets
      9. Z-Ordering (Stacking Components)
      10. The revalidate() and doLayout() Methods
      11. Managing Components
      12. Listening for Components
      13. Windows, Frames and Splash Screens
      14. Other Methods for Controlling Frames
      15. Content Panes
      16. Desktop Integration
    2. Events
      1. Event Receivers and Listener Interfaces
      2. Event Sources
      3. Event Delivery
      4. Event Types
      5. The java.awt.event.InputEvent Class
      6. Mouse and Key Modifiers on InputEvents
      7. Focus Events
    3. Event Summary
      1. Adapter Classes
      2. Dummy Adapters
    4. The AWT Robot!
    5. Multithreading in Swing
  19. 17. Using Swing Components
    1. Buttons and Labels
      1. HTML Text in Buttons and Labels
    2. Checkboxes and Radio Buttons
    3. Lists and Combo Boxes
    4. The Spinner
    5. Borders
    6. Menus
    7. Pop-Up Menus
      1. Component-Managed Pop Ups
    8. The JScrollPane Class
    9. The JSplitPane Class
    10. The JTabbedPane Class
    11. Scrollbars and Sliders
    12. Dialogs
      1. File Selection Dialog
      2. The Color Chooser
  20. 18. More Swing Components
    1. Text Components
      1. The TextEntryBox Application
      2. Formatted Text
      3. Filtering Input
      4. Validating Data
      5. Say the Magic Word
      6. Sharing a Data Model
      7. HTML and RTF for Free
      8. Managing Text Yourself
    2. Focus Navigation
      1. Trees
      2. Nodes and Models
      3. Save a Tree
      4. Tree Events
      5. A Complete Example
    3. Tables
      1. A First Stab: Freeloading
      2. Round Two: Creating a Table Model
      3. Round Three: A Simple Spreadsheet
      4. Sorting and Filtering
      5. Printing JTables
    4. Desktops
    5. Pluggable Look-and-Feel
    6. Creating Custom Components
      1. Generating Events
      2. A Dial Component
      3. Model and View Separation
  21. 19. Layout Managers
    1. FlowLayout
    2. GridLayout
    3. BorderLayout
    4. BoxLayout
    5. CardLayout
    6. GridBagLayout
      1. The GridBagConstraints Class
      2. Grid Coordinates
      3. The fill Constraint
      4. Spanning Rows and Columns
      5. Weighting
      6. Anchoring
      7. Padding and Insets
      8. Relative Positioning
      9. Composite Layouts
    7. Other Layout Managers
    8. Absolute Positioning
  22. 20. Drawing with the 2D API
    1. The Big Picture
    2. The Rendering Pipeline
    3. A Quick Tour of Java 2D
      1. Filling Shapes
      2. Drawing Shape Outlines
      3. Convenience Methods
      4. Drawing Text
      5. Drawing Images
      6. The Whole Iguana
    4. Filling Shapes
      1. Solid Colors
      2. Color Gradients
      3. Textures
      4. Desktop Colors
    5. Stroking Shape Outlines
    6. Using Fonts
      1. Font Metrics
    7. Displaying Images
      1. The Image Class
      2. Image Observers
      3. Scaling and Size
    8. Drawing Techniques
      1. Double Buffering
      2. Limiting Drawing with Clipping
      3. Offscreen Drawing
    9. Printing
  23. 21. Working with Images and Other Media
    1. Loading Images
      1. ImageObserver
      2. MediaTracker
      3. ImageIcon
      4. ImageIO
    2. Producing Image Data
      1. Drawing Animations
      2. BufferedImage Anatomy
      3. Color Models
      4. Creating an Image
      5. Updating a BufferedImage
    3. Filtering Image Data
      1. How ImageProcessor Works
      2. Converting an Image to a BufferedImage
      3. Using the RescaleOp Class
      4. Using the AffineTransformOp Class
    4. Saving Image Data
    5. Simple Audio
    6. Java Media Framework
  24. 22. JavaBeans
    1. What’s a Bean?
      1. What Constitutes a Bean?
    2. The NetBeans IDE
      1. Installing and Running NetBeans
    3. Properties and Customizers
    4. Event Hookups and Adapters
      1. Taming the Juggler
      2. Molecular Motion
    5. Binding Properties
      1. Constraining Properties
    6. Building Beans
      1. The Dial Bean
      2. Design Patterns for Properties
    7. Limitations of Visual Design
    8. Serialization Versus Code Generation
    9. Customizing with BeanInfo
      1. Getting Properties Information
    10. Handcoding with Beans
      1. Bean Instantiation and Type Management
      2. Working with Serialized Beans
      3. Runtime Event Hookups with Reflection
    11. BeanContext and BeanContextServices
    12. The Java Activation Framework
    13. Enterprise JavaBeans and POJO-Based Enterprise Frameworks
  25. 23. Applets
    1. The Politics of Browser-Based Applications
    2. Applet Support and the Java Plug-in
    3. The JApplet Class
      1. Applet Lifecycle
      2. The Applet Security Sandbox
      3. Getting Applet Resources
      4. The <applet> Tag
      5. Attributes
      6. Parameters
      7. ¿Habla Applet?
      8. The Complete <applet> Tag
      9. Loading Class Files
      10. Packages
      11. appletviewer
    4. Java Web Start
    5. Conclusion
  26. 24. XML
    1. The Butler Did It
    2. A Bit of Background
      1. Text Versus Binary
      2. A Universal Parser
      3. The State of XML
      4. The XML APIs
      5. XML and Web Browsers
    3. XML Basics
      1. Attributes
      2. XML Documents
      3. Encoding
      4. Namespaces
      5. Validation
      6. HTML to XHTML
    4. SAX
      1. The SAX API
      2. Building a Model Using SAX
      3. XMLEncoder/Decoder
    5. DOM
      1. The DOM API
      2. Test-Driving DOM
      3. Generating XML with DOM
      4. JDOM
    6. XPath
      1. Nodes
      2. Predicates
      3. Functions
      4. The XPath API
      5. XMLGrep
    7. XInclude
      1. Enabling XInclude
    8. Validating Documents
      1. Using Document Validation
      2. DTDs
      3. XML Schema
      4. The Validation API
    9. JAXB Code Binding and Generation
      1. Annotating Our Model
      2. Generating a Java Model from an XML Schema
      3. Generating an XML Schema from a Java Model
    10. Transforming Documents with XSL/XSLT
      1. XSL Basics
      2. Transforming the Zoo Inventory
      3. XSLTransform
      4. XSL in the Browser
    11. Web Services
    12. The End of the Book
  27. A. The Eclipse IDE
    1. The IDE Wars
    2. Getting Started with Eclipse
      1. Importing the Learning Java Examples
    3. Using Eclipse
      1. Getting at the Source
      2. The Lay of the Land
      3. Running the Examples
      4. Building the Ant-Based Examples
      5. Loner Examples
    4. Eclipse Features
      1. Coding Shortcuts
      2. Autocorrection
      3. Refactoring
      4. Diffing Files
      5. Organizing Imports
      6. Formatting Source Code
    5. Conclusion
  28. B. BeanShell: Java Scripting
    1. Running BeanShell
    2. Java Statements and Expressions
      1. Imports
    3. BeanShell Commands
    4. Scripted Methods and Objects
      1. Scripting Interfaces and Adapters
    5. Changing the Classpath
    6. Learning More . . .
  29. Glossary
  30. Index
  31. About the Authors
  32. Colophon
  33. Copyright
O'Reilly logo

A Quick Tour of Java 2D

Next we’ll embark on a quick tour of Java 2D, including working with shapes and text. We’ll finish with an example of Java 2D in action.

Filling Shapes

The simplest path through the rendering pipeline is filling shapes. For example, the following code creates an ellipse and fills it with a solid color. (This code would live inside a paint() method somewhere. We’ll present a complete, ready-to-run example a little later.)

    Shape c = new Ellipse2D.Float(50, 25, 150, 150); // x,y,width,height
    g2.setPaint(Color.blue);
    g2.fill(c);

Here, g2 is our Graphics2D object. The Ellipse2D shape class is abstract, but is implemented by concrete inner subclasses called Float and Double that work with float or double precision, respectively. The Rectangle2D class, similarly, has concrete subclasses Rectangle2D.Float and Rectangle2D.Double.

In the call to setPaint(), we tell Graphics2D to use a solid color, blue, for all subsequent filling operations. Next, the call to fill() tells Graphics2D to fill the given shape.

All geometric shapes in the 2D API are represented by implementations of the java.awt.geom.Shape interface. This interface defines methods that are common to all shapes, like returning a rectangle bounding box or testing if a point is inside the shape. The java.awt.geom package is a smorgasbord of useful shape classes, including Rectangle2D, RoundRectangle2D (a rectangle with rounded corners), Arc2D, Ellipse2D, and others. In addition, a few more basic classes in java.awt are Shapes: Rectangle, Polygon, and Area.

Drawing Shape Outlines

Drawing a shape’s outline is only a little bit more complicated. Consider the following example:

    Shape r = new Rectangle2D.Float(100, 75, 100, 100);
    g2.setStroke(new BasicStroke(4));
    g2.setPaint(Color.yellow);
    g2.draw(r);

Here, we tell Graphics2D to use a stroke that is four units wide and a solid color, yellow, for filling the stroke. When we call draw(), Graphics2D uses the stroke to create a new shape, the outline, from the given rectangle. The outline shape is then filled just as before; this effectively draws the rectangle’s outline. The rectangle itself is not filled.

Convenience Methods

Graphics2D includes quite a few convenience methods for drawing and filling common shapes; these methods are actually inherited from the Graphics class. Table 20-1 summarizes these methods. It’s a little easier to call fillRect() rather than instantiating a rectangle shape and passing it to fill().

Table 20-1. Shape-drawing methods in the graphics class

Method

Description

draw3DRect()

Draws a highlighted, 3D rectangle

drawArc()

Draws an arc

drawLine()

Draws a line

drawOval()

Draws an oval

drawPolygon()

Draws a polygon, closing it by connecting the endpoints

drawPolyline()

Draws a line connecting a series of points, without closing it

drawRect()

Draws a rectangle

drawRoundRect()

Draws a rounded-corner rectangle

fill3DRect()

Draws a filled, highlighted, 3D rectangle

fillArc()

Draws a filled arc

fillOval()

Draws a filled oval

fillPolygon()

Draws a filled polygon

fillRect()

Draws a filled rectangle

FillRoundRect()

Draws a filled, rounded-corner rectangle

As you can see, for each of the fill() methods in the table, there is a corresponding draw() method that renders the shape as an unfilled line drawing. With the exception of fillArc() and fillPolygon(), each method takes a simple x, y specification for the top-left corner of the shape and a width and height for its size.

The most flexible convenience method draws a polygon, which is specified by two arrays that contain the x and y coordinates of the vertices. Methods in the Graphics class take two such arrays and draw the polygon’s outline or fill the polygon.

The methods listed in Table 20-1 are shortcuts for more general methods in Graphics2D. The more general procedure is to first create a java.awt.geom.Shape object and then pass it to the draw() or fill() method of Graphics2D. For example, you could create a Polygon object from coordinate arrays. Since a Polygon implements the Shape interface, you can pass it to Graphics2D’s general draw() or fill() method.

The fillArc() method requires six integer arguments. The first four specify the bounding box for an oval—just like the fillOval() method. The final two arguments specify what portion of the oval we want to draw, as a starting angular position and an offset, both of which are specified in degrees. The zero-degree mark is at three o’clock; a positive angle is clockwise. For example, to draw the right half of a circle, you might call:

    g.fillArc(0, 0, radius * 2, radius * 2, -90, 180);

draw3DRect() automatically chooses shading colors by “darkening” the current color. So you should set the color to something other than black, which is the default (maybe gray or white); if you don’t, you’ll just get a black rectangle with a thick outline.

Drawing Text

Like drawing a shape’s outline, drawing text is just a simple variation on filling a shape. When you ask Graphics2D to draw text, it determines the shapes that need to be drawn and fills them. The shapes that represent characters are called glyphs. A font is a collection of glyphs. Here’s an example of drawing text:

    g2.setFont(new Font("Times New Roman", Font.PLAIN, 64));
    g2.setPaint(Color.red);
    g2.drawString("Hello, 2D!", 50, 150);

When we call drawString(), Graphics2D uses the current font to retrieve the glyphs that correspond to the characters in the string. Then the glyphs (which are really just Shapes) are filled using the current Paint.

Drawing Images

Images are treated a little differently than shapes. In particular, the current Paint is not used to render an image because the image contains its own color information for each pixel (it is the paint, effectively). The following example loads an image from a file and displays it:

    Image i = Toolkit.getDefaultToolkit().getImage("camel.gif");
    g2.drawImage(i, 75, 50, this);

In this case, the call to drawImage() tells Graphics2D to place the image at the given location. We’ll explain the fourth argument, which is used for monitoring image loading later.

Transformations and rendering

Four parts of the pipeline affect every graphics operation. In particular, all rendering is subject to being transformed, composited, and clipped. Rendering hints are used to affect all of Graphics2D’s rendering.

This example shows how to modify the current transformation with a translation and a rotation:

    g2.translate(50, 0);
    g2.rotate(Math.PI / 6);

Every graphics primitive drawn by g2 will now have this transformation applied to it (a shift of 50 units right and a rotation of 30 degrees clockwise). We can have a similarly global effect on compositing:

    AlphaComposite ac = AlphaComposite.getInstance(
        AlphaComposite.SRC_OVER, (float).5);
    g2.setComposite(ac);

Now, every graphics primitive we draw will be half transparent; we’ll explain more about this later.

All drawing operations are clipped by the current clipping shape, which is any object implementing the Shape interface. In the following example, the clipping shape is set to an ellipse:

    Shape e = new Ellipse2D.Float(50, 25, 250, 150);
    g2.clip(e);

You can obtain the current clipping shape using getClip(); this is handy if you want to restore it later using the setClip() method.

Finally, the rendering hints influence all drawing operations. In the following example, we tell Graphics2D to use anti-aliasing, a technique that smoothes out the rough pixel edges of shapes and text:

    g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
        RenderingHints.VALUE_ANTIALIAS_ON);

The RenderingHints class contains other keys and values that represent other rendering hints. If you really like to fiddle with knobs and dials, this is a good class to check out.

The Whole Iguana

Let’s put everything together now, just to show how graphics primitives travel through the rendering pipeline. The following example demonstrates the use of Graphics2D from the beginning to the end of the rendering pipeline. With very few lines of code, we are able to draw some pretty complicated stuff (see Figure 20-2).

Here’s the code:

    //file: Iguana.java
    import java.awt.*;
    import java.awt.event.*;
    import java.awt.geom.*;
    import javax.swing.*;

    public class Iguana extends JComponent {
      private Image image;
      private int theta;

      public Iguana() {
        image = Toolkit.getDefaultToolkit().getImage(
            "Piazza di Spagna.small.jpg");
        theta = 0;
        addMouseListener(new MouseAdapter() {
          public void mousePressed(MouseEvent me) {
            theta = (theta + 15) % 360;
            repaint();
          }
        });
      }

      public void paint(Graphics g) {
        Graphics2D g2 = (Graphics2D)g;

        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
            RenderingHints.VALUE_ANTIALIAS_ON);

        int cx = getSize().width / 2;
        int cy = getSize().height / 2;

        g2.translate(cx, cy);
        g2.rotate(theta * Math.PI / 180);

        Shape oldClip = g2.getClip();
        Shape e = new Ellipse2D.Float(-cx, -cy, cx * 2, cy * 2);
        g2.clip(e);

        Shape c = new Ellipse2D.Float(-cx, -cy, cx * 3 / 4, cy * 2);
        g2.setPaint(new GradientPaint(40, 40, Color.blue,
            60, 50, Color.white, true));
        g2.fill(c);

        g2.setPaint(Color.yellow);
        g2.fillOval(cx / 4, 0, cx, cy);

        g2.setClip(oldClip);

        g2.setFont(new Font("Times New Roman", Font.PLAIN, 64));
        g2.setPaint(new GradientPaint(-cx, 0, Color.red,
            cx, 0, Color.black, false));
        g2.drawString("Hello, 2D!", -cx * 3 / 4, cy / 4);

        AlphaComposite ac = AlphaComposite.getInstance(
            AlphaComposite.SRC_OVER, (float).75);
        g2.setComposite(ac);

        Shape r = new RoundRectangle2D.Float(0, -cy * 3 / 4,
            cx * 3 / 4, cy * 3 / 4, 20, 20);
        g2.setStroke(new BasicStroke(4));
        g2.setPaint(Color.magenta);
        g2.fill(r);
        g2.setPaint(Color.green);
        g2.draw(r);

        g2.drawImage(image, -cx / 2, -cy / 2, this);
      }

      public static void main(String[] args) {
        JFrame frame = new JFrame("Iguana");
        frame.setLayout(new BorderLayout());
        frame.add(new Iguana(), BorderLayout.CENTER);
        frame.setSize(300, 300);
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.setVisible(true);
      }
    }
Exercising the 2D API

Figure 20-2. Exercising the 2D API

The Iguana class is a subclass of JComponent with a very fancy paint() method. The main() method takes care of creating a JFrame that holds the Iguana component.

Iguana’s constructor loads a small image (we’ll talk more about this later) and sets up a mouse event handler. This handler changes a member variable, theta, and repaints the component. Each time you click, the entire drawing is rotated by 15 degrees.

Iguana’s paint() method does some pretty interesting stuff, but none of it is very difficult. First, user space is transformed so that the origin is at the center of the component. The user space is then rotated by theta:

    g2.translate(cx, cy);
    g2.rotate(theta * Math.PI / 180);

Iguana saves the current (default) clipping shape before setting it to a large ellipse. Then, Iguana draws two filled ellipses. The first is drawn by instantiating an Ellipse2D and filling it; the second is drawn using the fillOval() convenience method. (We’ll talk about the color gradient in the first ellipse in the next section.) As you can see in Figure 20-2, both ellipses are clipped by the elliptical clipping shape. After filling the two ellipses, Iguana restores the old clipping shape.

Next, Iguana draws some text (see the section Using Fonts). The next action is to modify the compositing rule as follows:

    AlphaComposite ac = AlphaComposite.getInstance(
        AlphaComposite.SRC_OVER, (float).75);
    g2.setComposite(ac);

The only thing this means is that we want everything to be drawn with transparency. The AlphaComposite class defines constants that represent different compositing rules, much the way the Color class contains constants that represent different predefined colors. In this case, we’re asking for the source over destination rule (SRC_OVER), but with an additional alpha multiplier of 0.75. Source over destination means that whatever we’re drawing (the source) should be placed on top of whatever’s already there (the destination). The alpha multiplier means that everything we draw will be treated at 0.75, or three quarters, of its normal opacity, allowing the existing drawing to “show through.”

You can see the effect of the new compositing rule in the rounded rectangle and the image, which both allow previously drawn elements to show through.

The best content for your career. Discover unlimited learning on demand for around $1/day.