Java Bean properties

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Property

• Property is a public attribute of a bean that you can manipulate via getter and setter methods

• Properties typically correspond to fields that define the internal state of an object.

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Properties

Active properties:Changing of a property can result in the firing of an event, these are called active properties. Active properties can be Bound or Constrained.

Bound and Constrained properties:Events used to notify, when a property is changed for a bean.

Standalone properties: It is standalone, which in this case means that it is not

connected to via events to listeners.

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Simple Properties

• getXXX() – accessor method to access internal variable

• isXXX() – accessor method to flag to the introspector a single valued boolean property

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Simple Propertiespublic class person{private int age;private boolean single;person(int newage){age=newage;}public int getAge(){return age;}public void setSingle(boolean status){single=status;}public boolean isSingle(){return single;}}

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Multi-valued indexed properties

An indexed property contains a collection of values that are of same type.Ex:public class myfriends{private String friends[];myfriends(String[] list){friends=list;}public String getfriends(int index){return friends[index];}public String[] getfriends(){return friends;}

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Bound Properties classes and interfaces

PropertyChangeSupport

addPropertyChangeListener

removePropertyChangeListener

firePropertyChange

Object class

PropertyChangeSupport class

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Bound Properties classes and interfaces

PropertyChange

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EventListenerinterface

PropertyChangeListener interface

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Bound Properties classes and interfaces

PropertyChangeEvent

getPropertyName

getNewValue

EventObject class

PropertyChangeEvent class

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Constrained Properties classes and interfaces

VetoableChangeSupport

addVetoableChangeListener

removeVetoableChangeListener

fireVetoableChange

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Object class

VetoableChangeSupport

class

PropertyVetoException

getPropertyChangeEvent

Exception class EventListener interface

PropertyVetoException class

VetoableChangeVetoableChangeListener

interface

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The Persistent bean streaming classes and interfaces

public class MyBean { String prop1; public String getProp1() { return prop1; } public void setProp1(String s) { prop1 = s; } }

Bean Instantiation

try {MyBean bean =

(MyBean)Beans.instantiate(ClassLoader.getSystemClassLoader(), "MyBean");

} catch (ClassNotFoundException e) {} catch (IOException e) {}

Getting and setting properties of a bean

Object o = new MyBean();try { // Get the value of prop1 Expression expr = new Expression(o, "getProp1", new Object[0]);

expr.execute(); String s = (String)expr.getValue(); // Set the value of prop1 Statement stmt = new Statement(o, "setProp1", new Object[]{"new

string"}); stmt.execute();}catch (Exception e) {}

//implementing a bound property

• // Create the listener list.• PropertyChangeSupport pcs = new PropertyChangeSupport(this);• // The listener list wrapper methods.• public synchronized void

addPropertyChangeListener(PropertyChangeListener listener) { pcs.addPropertyChangeListener(listener);}

• public synchronized void removePropertyChangeListener(PropertyChangeListener listener) { pcs.removePropertyChangeListener(listener);}

//implementing a bound property

int myProperty;public int getMyProperty() { return myProperty;}public void setMyProperty(int newValue) { int oldValue = myProperty; myProperty = newValue;

pcs.firePropertyChange("myProperty", new Integer(oldValue), new Integer(newValue));

}

//implementing constrained property

// Create the listener list.VetoableChangeSupport vcs = new VetoableChangeSupport (this); // The listener list wrapper methods.public synchronized void addVetoableChangeListener

(VetoableChangeListener listener) { vcs.addVetoableChangeListener(listener);}

public synchronized void removeVetoableChangeListener (VetoableChangeListener listener) { vcs.removeVetoableChangeListener(listener);}

//implementing constrained property

int myProperty;public int getMyProperty() { return myProperty;}public void setMyProperty(int newValue) throws

PropertyVetoException { try { vceListeners.fireVetoableChange( "myProperty", new

Integer(myProperty), new Integer(newValue)); myProperty = newValue; } catch (PropertyVetoException e) { throw e; }}

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Reflection classes

Object class

Classs classBeans

introspection classes

Method class Array class Constructor class Field class Modifier class

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The enhanced Class classtoString Class class getClasses

forName getFields

newInstance getMethods

isInstance getConstructors

isAssignableForm getField

isInterface getMethod

isArray getConstructor

isPrimitive getDeclaredClass

getName getDeclaredFields

getClassLoader getDeclaredMethods

getSuperClass getDeclaredConstructors

getInterface getDeclaredField

getComponentType getDeclaredMethod

getModifiers getDeclaredConstructor

getSigners getResourceAsStream

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The Reflective Method ClassgetDeclaringClass Method Class getExceptionTypes

getName equals

getModifiers hashCode

getReturnType toString

getParameterTypes invoke

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Java beans Introspection: An Overview

Object class

SimpleBeanInfo class Introspector class

MethodDescriptor class

EventSetDescriptor class

PropertyDescriptor class

ParameterDescriptor class

BeanDescriptor class

FeatureDescriptor class

BeanInfo classIndexedProper

tyDescriptor class

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JavaBeans Introspection:The descriptor classesFeatureDescriptor FeatureDescriptor

ClassisHidden

getName setHiddensetName getShortDescriptiongetDisplayName setShortDescriptionsetDisplayName setValueisExpert getValuesetExpert attributeName

BeanDescriptor BeanDescriptor ClassgetBeanClass

getCustomizerClass

MethodDescriptor MethodDescriptor ClassgetMethod

getParameterDescriptors

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EventSetDescriptor EventSetDescriptor class

getRemoveListenerMethod

getListenerType setUnicast

getListernerMethods isUnicast

getListernerMethodDescriptors

setinDefaultEventSet

getAddListenerMethod isInDefaultEventSet

PropertyDescriptor PropertyDescriptoer Class

setBound

getPropertyType isConstrained

getReadMethod setConstrained

getWriteMethod setPropertyEditorClass

isBound getPropertyEditorClass

ParameterDescriptor ParameterDescriptor Class

IndexedPropertyDescriptor

IndexedPropertyDescriptor Class

getIndexedReadMethodgetIndexedWriteMethodgetIndexedPropertyType

//listing the properties of a bean

try { BeanInfo bi = Introspector.getBeanInfo(MyBean.class);

PropertyDescriptor[] pds = bi.getPropertyDescriptors(); for (int i=0; i<pds.length; i++) { // Get property name String propName = pds[i].getName(); } catch (java.beans.IntrospectionException e) {}