Introspection thro’ Reflection

1. Introspection thro’ Reflection Reflection: • Ability of the program to Analyze itself • Java.lang.reflect package • Can obtain information about the • Fields • Constructor • Method • Modifiers of the class • With this information the class can be instantiated and the methods can be invoked dynamically

2. Introspection • Why do we need it? • When beans are used in a IDE (Integrated Development Environment), its properties and methods are need to be exposed so that builder tool and the programmer can control the appearance and the behavior of the bean. • Design Pattern provides all the information • For accessing Read/write property we use getPropertyName() and setPropertyName() methods • Reflection mechanism in java will analyze and provide the information that a property “PropertName”.

3. How introspection Works? • Provide information about the bean explicitly • Self-description provided by the bean. • Class implements the java.bean.BeanInfo interface • Which in turn specifies a set of function that are used to collect information about the bean. • Reflection – Analyze the class itself • Introspection – uses the meta-object(BeanInfo)

4. BeanInfo • Follows a special design pattern • Always the Bean class which is having the BeanInfo object should have suffix ‘BeanInfo’ • BeanInfo can be accessed and modified using getBeanInfoSearchPath() and setBeanInfoSearchPath()

5. java.beans.BeanInfo Methods Int Constant • getIcon(int) • Returns an image to be used to represent the bean in toolboxes, toolbars, etc. FeatureDescriptor • getBeanDescriptor() • Returns overall information about the bean, such as its displayName, • getMethodDescriptors() • Returns a list of methods supported by the bean with a description of each method • getPropertyDescriptors() • Returns a list of properties supported by the bean with a description of each property

6. getEventSetDescriptors() • Returns a list of events fired by the bean with a description of each event • getAdditionalBeanInfo() • This method allows a BeanInfo object to return an arbitrary collection of other BeanInfo objects that provide additional information on the current bean • getDefaultEventIndex() • A bean may have a "default" event that is the event that will mostly commonly be used by human's when using the bean • getDefaultPropertyIndex() • A bean may have a "default" property that is the property that will mostly commonly be initially chosen for update by human's who are customizing the bean

7. getIcon import java.beans.*; public class IntroBeanInfo extends SimpleBeanInfo { public java.awt.Image getIcon(int iconType) { if(iconType ==BeanInfo.ICON_COLOR_16x16) { System.err.println("True"); java.awt.Image img = loadImage("jugg.gif"); return img; } return null; } }

8. There are four types of icon supported: • ICON_MONO_16x16 • ICON_COLOR_16x16 • ICON_MONO_32x32 • ICON_COLOR_32x32 • These constants are defined in java.beans.BeanInfo • The sizes refer to the pixel size of the imagesloadImage is defined in java.beans. SimpleBeanInfopublic Image loadImage(String resourceName) • resourceName - A pathname relative to the directory holding the class file of the current class. For example, "wombat.gif".

9. java.beans.FeatureDescriptor • Most of the methods in java.beans.BeanInfo return descriptors • java.beans.FeatureDescriptor is the parent class for all bean descriptorssetDisplayName(String) getDisplayName() • The name displayed in builder tool for this item • setName(String) getName() • The programmatic name of the property/method/event • setShortDescription(String) getShortDescription() • You can associate a short descriptive string with a feature

10. attributeNames() setValue(String, Object) getValue(String) • Supports name/value pairs with this feature • setExpert(boolean) isExpert() • Distinguishes between features for expert users from those for normal users • setHidden(boolean) isHidden() • Identifies features that are intended only for tool use, and which should not be exposed to humans

11. getBeanDescriptor public BeanDescriptor getBeanDescriptor() { BeanDescriptor bd = new BeanDescriptor( Intro.class ); bd.setDisplayName( "Pink"); return bd; }

12. PropertyDescriptor • public PropertyDescriptor(String propertyName, Method getter, Method setter) throws IntrospectionException • propertyName • The programmatic name of the property • getter • The method used for reading the property value. Set null if the property is write-only • setter • The method used for writing the property value. Set null if the property is read-only

13. public PropertyDescriptor[] getPropertyDescriptors() { try { PropertyDescriptor nameProperty = new PropertyDescriptor( "color", Intro.class ); nameProperty.setDisplayName( "Color"); nameProperty.setShortDescription( "Color of the box"); PropertyDescriptor[] allProperties = { nameProperty }; return allProperties; } catch ( IntrospectionException error ) { return super.getPropertyDescriptors(); // use default if there is an error } }

14. Event Descriptos • Expose the events that are fired by the bean • Implement the method ‘getEventSetDescriptors()’ Public EventSetDescriptor(Class sourceClass, String eventSetName, String listenerMethodName)throws IntrospectionException

15. Customization • A bean can be customized for enhancing its funtionality • Through Property Editors • Through Customizer Classes

16. Property Editors • Allows the user to read and change the value of the property • To create aProperty Editor we need the PropertyEditor interface and the PropertyEditorSupport class • PropertyEditor  provides support for GUIs that permit users to edit property value • setAsText and getAsText are overridden

17. Cutomizer Class • Implementing the java.beans.Customizer interface • setObject of the class that implements customizer are overridden.