Indexed Properties in Javabeans

Indexed Properties:

An indexed property consists of multiple values. It can be identified by the following design patterns, where N is the name of the property and T is its type:

public T getN(int index);
public void setN(int index, T value);
public T[ ] getN( );
public void setN(T values[ ]);
Here is an indexed property called data along with its getter and setter methods:
private double data[ ];
public double getData(int index) {
return data[index];
public void setData(int index, double value) {
data[index] = value;
public double[ ] getData( ) {
return data;
public void setData(double[ ] values) {
data = new double[values.length];
System.arraycopy(values, 0, data, 0, values.length);

Design Patterns for Events:
Beans uses the delegation event model that was discussed earlier in this book. Beans can generate events and send them to other objects. These can be identified by the following design-patterns, where T is the type of the event:

public void addTListener(TListener eventListener)
public void addTListener(TListener eventListener)
throws java.util.TooManyListenersException
public void removeTListener(TListener eventListener)

Using the BeanInfo Interface:
As the preceding discussion shows, design patterns implicitly determine what information is available to the user of a Bean. The BeanInfo interface enables you to explicitly control what information is available. The BeanInfo interface defines several methods, including these:

PropertyDescriptor[ ] getPropertyDescriptors( )
EventSetDescriptor[ ] getEventSetDescriptors( )
MethodDescriptor[ ] getMethodDescriptors( )

They return arrays of objects that provide information about the properties, events, and methods of a Bean. The classes PropertyDescriptor, EventSetDescriptor, and MethodDescriptor are defined within the [java]java.beans [/java]package and they describe the indicated elements. By implementing these methods, a developer can designate exactly what is presented to a user, bypassing introspection based on design patterns.

When creating a class that implements BeanInfo, you must call that class bnameBeanInfo, where bname is the name of the Bean. For example, if the Bean is called MyBean, then the information class must be called MyBeanBeanInfo.