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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

Handcoding with Beans

So far, we’ve seen how to create and use beans within a bean application builder environment. That is the primary motivation for JavaBeans, at least in GUI development. But beans are not limited to being used by automated tools. There’s no reason we can’t use beans in handwritten code. You could use a builder to assemble beans for the user interface of your application and then load that serialized bean or a collection of beans in your own code, just as NetBeans does when told to use object serialization. We’ll give an example of that in a moment.

Bean Instantiation and Type Management

Beans are an abstraction over simple Java classes. They add, by convention, features that are not part of the Java language. To enable certain additional capabilities of JavaBeans, we use special tools that take the place of basic language operations. Specifically, when working with beans, we are provided with replacements for three basic Java operations: creating an object with new, checking the type of an object with the instanceof operator, and casting a type with a cast expression. In place of these, use the corresponding static methods of the java.beans.Beans class, shown in Table 22-1.

Table 22-1. Methods of the java.beans.Beans class

Operator

Equivalent

New

Beans.instantiate(classloader, name)

Instanceof

Beans.isInstanceOf(object, class)

Beans.instantiate() is the new operation for beans. It takes a class loader and the name of a bean class or serialized bean as arguments. Its advantage over the plain new operator is that it can also load beans from a serialized form. If you use instantiate(), you don’t have to specify in advance whether you will provide the bean as a class or as a serialized object. The instantiate() method first tries to load a resource file based on the name bean, by turning package-style names (with dots) into a path-style name with slashes and then appending the suffix .ser. For example, magicbeans.NumericField becomes magicbeans/NumericField.ser. If the serialized form of the bean is not found, the instantiate() method attempts to create an instance of the class by name.[47]

Beans.isInstanceOf() and Beans.getInstanceOf() do the jobs of checking a bean’s type and casting it to a new type. These methods were intended to allow one or more beans to work together to implement “virtual” or dynamic types. They are supposed to allow beans to take control of this behavior, providing different “views” of themselves. However, they currently don’t add any functionality and aren’t widely used.

Working with Serialized Beans

Remember the Juggler we serialized a while back? Well, it’s time to revive him, just like Han Solo from his “Carbonite” tomb in Star Wars. We’ll assume that you saved the Juggler by flipping on the Serialization property while working with the LearnJava1 class and that NetBeans, therefore, saved him in the file LearnJava1_juggler1.ser. If you didn’t do this, you can use the following snippet of code to serialize the bean to a file of your choice:

    // Serialize a Juggler instance to a file...
    import magicbeans.sunw.demo.juggler.Juggler;
    import java.io.*;
     
    public class SerializeJuggler {
       public static void main( String [] args ) throws Exception
       {
          Juggler duke = new Juggler();
          ObjectOutputStream oout = new ObjectOutputStream(
             new FileOutputStream("juggler.ser") );
          oout.writeObject( duke );
          oout.close();
       }
    }

Once you have the frozen Juggler, compile the following small application:

    //file: BackFromTheDead.java
    import java.awt.Component;
    import javax.swing.*;
    import java.beans.*;
      
    public class BackFromTheDead extends JFrame {
      
      public BackFromTheDead( String name ) {
        super("Revived Beans!");
        try {
          Object bean = Beans.instantiate(
            getClass().getClassLoader(), name );
      
          if ( Beans.isInstanceOf( bean, JComponent.class) ) {
            JComponent comp = (JComponent)
              Beans.getInstanceOf(bean, JComponent.class);
            getContentPane().add("Center", comp);
          } else {
              System.out.println("Bean is not a JComponent...");
          }
        } catch ( java.io.IOException e1 ) {
          System.out.println("Error loading the serialized object");
        } catch ( ClassNotFoundException e2 ) {
          System.out.println(
             "Can't find the class that goes with the object");
        }
      }
      
      public static void main(String [] args) {
        JFrame frame = new BackFromTheDead( args[0] );
        frame.pack();
        frame.setVisible(true);
      }
    }

Run this program, passing the name of your serialized object as an argument and making sure that our magicbeans.jar file is in your classpath. The name should not include the .ser extension in the name; the Beans.instantiate() method adds this automatically in its search for the serialized or class version. The juggler should spring back to life, juggling once again as shown in Figure 22-9.

The restored Juggler

Figure 22-9. The restored Juggler

In BackFromTheDead, we use Beans.instantiate() to load our serialized bean by name. We then check to see whether it is a GUI component using Beans.isInstanceOf(). (It is, because the Juggler is a subclass of java.awt.Component.) Finally, we cast the instantiated object to a Component with Beans.getInstanceOf() and add it to our application’s JFrame. Notice that we still need a static Java cast to turn the Object returned by getInstanceOf() into a JComponent. This cast may seem gratuitous, but it is the bridge between the dynamic beans lookup of the type and the static, compile-time view of the type.

Everything we’ve done here could be done using the plain java.io.ObjectInputStream discussed in Chapter 12. But these bean management methods are intended to shield the user from details of how the beans are implemented and stored.

One more thing before we move on. We blithely noted that when the Juggler was restored, the bean began juggling again. This implies that threads were started when the bean was deserialized. Serialization doesn’t automatically manage transient resources such as threads or even loaded images, but it’s easy to take control of the process to finish reconstructing the bean’s state when it is deserialized. Have a look at the Juggler source code (provided with the examples) and refer to Chapter 12 for a discussion of object deserialization using the readObject() method.

Runtime Event Hookups with Reflection

We’ve discussed reflection largely in terms of how design tools use it to analyze classes. Today, reflection is frequently finding its way into applications to perform dynamic activities that wouldn’t be possible otherwise. In this section, we’ll look at a dynamic event adapter that can be configured at runtime.

In Chapter 16, we saw how adapter classes could be built to connect event firings to arbitrary methods in our code, allowing us to cleanly separate GUI and logic in our applications. In this chapter, we have seen how NetBeans interposes this adapter code between beans to do this for us.

The AWT/Swing event model reduces the need to subclass components to perform simple hookups. If we start relying heavily on special adapter classes, we can quickly end up with as many adapters as components. Anonymous inner classes let us hide these classes, but they’re still there. A potential solution for large or specialized applications is to create generic event adapters that serve a number of event sources and targets simultaneously.

The java.beans.EventHandler is a dynamic event dispatcher that simply calls methods in response to events. What makes the EventHandler unusual in Java is that it is the first standard utility to use reflection to allow us to specify the method by name. In other words, you ask the EventHandler to direct events to a handler by specifying the handler object and the string name of the method to invoke on that object.

We can use the create() method of EventHandler to get an adapter for a specified type of event listener, specifying a target object and method name to call when that event occurs. The target object doesn’t have to be a listener for the particular event type or any other particular kind of object. The following application, DynamicHookup, uses the EventHandler to connect a button to a launchTheMissiles() method in our class:

    //file: DynamicHookup.java
    import javax.swing.*;
    import java.awt.event.*;
    import java.beans.EventHandler;

    public class DynamicHookup extends JFrame {
      JLabel label = new JLabel( "Ready...", JLabel.CENTER );
      int count;

      public DynamicHookup() {
        JButton launchButton = new JButton("Launch!");
        getContentPane().add( launchButton, "South" );
        getContentPane().add( label, "Center" );
            launchButton.addActionListener(
                    (ActionListener)EventHandler.create(
                            ActionListener.class, this, "launchTheMissiles"));
      }
      public void launchTheMissiles() {
        label.setText("Launched: "+ count++ );
      }

      public static void main(String[] args) {
        JFrame frame = new DynamicHookup();
            frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.setSize(150, 150);
        frame.setVisible( true );
      }
    }

Here, we call the EventHandler’s create() method, passing it the ActionListener class, the target object (this), and a string with the name of the method to invoke on the target when the event arrives. EventHandler internally creates a listener of the appropriate type and registers our target information. Not only do we eliminate an inner class, but the implementation of EventHandler may allow it to share adapters internally, producing very few objects.

This example shows how we would call a method that takes no arguments—but the EventHandler can actually do more, setting JavaBeans properties in response to events. The following form of create() tells EventHandler to call the launchTheMissiles() method, passing the source property of the ActionEvent as an argument:

    EventHandler.create(
       ActionListener.class, target, "launchTheMissiles", "source")

All events have a source property (via the getSource() method), but we can go further, specifying a chain of property “gets” separated by dots, which are applied before the value is passed to the method. For example:

    EventHandler.create(
       ActionListener.class, target, "launchTheMissiles", "source.text")

The source.text parameter causes the value getSource().getText() to be passed as an argument to launchTheMissiles(). In our case, that would be the label of our button. Other forms of create() allow more flexibility in selecting which methods of a multimethod listener interface are used as well as other options. We won’t cover every detail of the tool here.

How it works

The EventHandler uses the java.lang.reflect.Proxy, which is a factory that can generate adapters implementing any type of interface at runtime. By specifying one or more event listener interfaces (e.g., ActionListener), we get an adapter that implements those listener interfaces generated for us on the fly. The adapter is a specially created class that delegates all the method calls on its interfaces to a designated InvocationHandler object. See Chapter 1 for more information about proxy classes.



[47] This feature would seemingly be applicable to XML-serialized Java beans using the XMLOutputStream as well, but it is not currently implemented for them. This is another sign that the JavaBeans APIs have stagnated.

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