Java Beans

JAVA BEANS 2 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM Overview  The Bean-Writing Process  Using Beans to Build an Application  Naming Patterns for Bean Properties and Events  Bean Property Types  Beaninfo Classes  Property Editors  Customizers  Javabeans Persistence continued 3 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM What is a JavaBean?  A JavaBean is a component:  a self-contained, reusable software unit  it can be visually composed with other beans to make bigger compo nents, applets, applications, etc. continued 4 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM  A bean is designed to expose its features:  e.g. public methods, properties (data), events  Exposure allows beans to be used inside visual building tools (e.g. JBuilder)  Exposure is based on coding rules that a programmer must follow when writing a bean  these rules are mostly standard naming conventions for methods continued 5 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM  Beans are persistent  their data is automatically stored when the program using them finishes  the data is restored when the program next starts  persistence is implemented in JavaBeans by using Java's object seriali zation features 6 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM How Builder Tools Use Beans  Builder tools (e.g JBuilder, Bean Builder) know a bean's features by looking at its publi c methods, properties and events  called introspection  implemented using Java's reflection classes  A builder can also examine a bean's information object (BeanInfo), if the progra mmer has included one. continued 7 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM  A builder will have visual support for setting/ reading a bean's properties, and for accessing its methods.  A builder will be able to 'link' beans based on events  a source bean can send an event to a listener bean 8 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM From Package to JAR  A JAR file must contain a manifest  it lists the contents of the JAR file  a programmer writes the manifest in the manifest.tmp file  When the JAR file is being created, the jar utility converts manifest.tmp into a MANIF EST.MF file stored in the META_INF director y of the JAR file. 9 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM manifest.tmp example Name: myPackage/myBeanClass.class Java-Bean: True  A Name line says where a bean is located in the JAR file.  '/' is used instead of Java's '.' continued 10 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM  There may be many classes (and other resources) in a JAR file  each has its own Name and Java-Bean line  Not all the resources in a JAR file need to be beans; if a class is a be an then the Java-Bean line is set to t rue (otherwise false)  beans will appear in the Toolbox window [...]... listed Create by Võ Văn Hải-Khoa CNTT- 12 Run the JAR file  c:> java -jar LogoAnimator.jar    run the application in the bean java uses the manifest file to execute main() of Main-Class java the name of the class to execute: c:> java -cp myJar.jar myPackage.myClass Or give Create by Võ Văn Hải-Khoa CNTT- 13 Kinds of Properties  JavaBeans have 4 kinds of properties, which are supported in different... Example SliderFieldPanel Bean JSlider and a JTextField  A  A change to either should affect the other, and any listener objects should be notified Create by Võ Văn Hải-Khoa CNTT- 25 Listening Beans Format  Beans that are registered listeners for property changes must implement the PropertyChangeListener interface  The interface has one method:  void propertyChange(PropertyChangeEvent e)  it is... i) { return values[i]; } public void setValues(int i, double v) { values[i] = v; } Create by Võ Văn Hải-Khoa CNTT- 22 Bound Properties  A bean with a bound property will notify other listening objects /beans when the property changes  The programmer must add the listeners to a collection of PropertyChangeListeners  sometimes called registering the listeners Create by Võ Văn Hải-Khoa CNTT- continued... properties, which are supported in different ways:     simple properties indexed properties bound properties constrained properties Create by Võ Văn Hải-Khoa CNTT- 14 Naming Patterns  The designers of the Java specification decided not to add keywords to the language to support vis ual programming  Builder tool could analyze a bean to learn its properties or events  There are two alternative mechanisms... changeSupport.firePropertyChange( ) vetoSupport is used in a similar way to changeSupport:  vetoable listeners must be registered with it via public add/remove methods Create by Võ Văn Hải-Khoa CNTT- 32 Vetoable Listener Code  Beans that are registered vetoable listeners for property changes must implement the Vetoa bleChangeListener interface  The interface has one method:  void vetoableChange (PropertyChangeEvent e)  it . restored when the program next starts  persistence is implemented in JavaBeans by using Java's object seriali zation features 6 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM How Builder Tools Use. Properties and Events  Bean Property Types  Beaninfo Classes  Property Editors  Customizers  Javabeans Persistence continued 3 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM What is a JavaBean?  A. myJar.jar myPackage.myClass 14 Create by Võ Văn Hải-Khoa CNTT- ĐHCN Tp.HCM Kinds of Properties  JavaBeans have 4 kinds of properties, which are supported in different ways:  simple properties  indexed