The Java Beans API

The Java Beans API

The Java Beans functionality is provided by a set of classes and interfaces in the java.beans package. This section provides a brief overview of its contents. Table 37-1 lists the interfaces in java.beans and provides a brief description of their functionality. Table 37-2 lists the classes in java.beans.

Although it is beyond the scope of this chapter to discuss all of the classes, four are of particular interest: Introspector, PropertyDescriptor, EventSetDescriptor, and MethodDescriptor. Each is briefly examined here.

Introspector

The Introspector class provides several static methods that support introspection. Of most interest is getBeanInfo( ). This method returns a BeanInfo object that can be used to obtain information about the Bean. The getBeanInfo( ) method has several forms, including the one shown here:

static BeanInfo getBeanInfo(Class<?> bean) throws IntrospectionException The returned object contains information about the Bean specified by bean.

PropertyDescriptor

The PropertyDescriptor class describes the characteristics of a Bean property. It supports several methods that manage and describe properties. For example, you can determine if a property is bound by calling isBound( ). To determine if a property is constrained, call isConstrained( ). You can obtain the name of a property by calling getName( ).

EventSetDescriptor

The EventSetDescriptor class represents a Bean event. It supports several methods that obtain the methods that a Bean uses to add or remove event listeners, and to otherwise manage events. For example, to obtain the method used to add listeners, call getAddListenerMethod( ). To obtain the method used to remove listeners, call getRemoveListenerMethod( ). To obtain the type of a listener, call getListenerType( ). You can obtain the name of an event by calling getName( ).

MethodDescriptor

The MethodDescriptor class represents a Bean method. To obtain the name of the method, call getName( ). You can obtain information about the method by calling getMethod( ), shown here:

Method getMethod( )

An object of type Method that describes the method is returned.