Lesson 1

This module continues with the study of Bean structure by examining introspection and how Beans expose information about themselves.
You learn about the two different approaches to introspection supported by JavaBeans:

1. automatically using design patterns or
2. explicitly using a special class in the JavaBeans API (see below).

The reference to the JavaBeans API might at first seem confusing since JavaBeans is technically a part of the Java API.
However, JavaBeans initially began as a separate API and was only merged with the Java API in Java 1.1. It is sometimes helpful to refer to the JavaBeans subset of the Java API as the JavaBeans API.
This distinction also helps to clarify the relationship between JavaBeans and Java:
Java is a programming language, runtime system, and API, whereas JavaBeans is simply a subset of the Java API.

The following points describe the JavaBeans standard component architecture for Java.

1. JavaBeans API is packaged in java.beans
2. This package includes interfaces and classes that support design and/or runtime operations.

It's common to separate the implementation into design-only and runtime classes,

1. the design-oriented classes (which assist programmers during component assembly) do not have to be shipped with a finished application.
2. The JavaBeans architecture fully supports this implementation strategy.

The module culminates in the complete development of a basic Bean, which draws upon much of what you have learned throughout the entire course thus far.

In the context of JavaBeans, a component model for Java, introspection is a critical feature that facilitates the discovery and manipulation of JavaBeans' properties, events, and methods. Typically, introspection in JavaBeans is approached through a blend of reflection and custom code, leveraging Java's Reflection API. When a tool, like an IDE or a builder tool, needs to interact with a JavaBean, it relies on introspection to understand the bean's capabilities. This process involves analyzing the bean's class to determine its properties, events, and public methods, which are then presented to the developer or used by the tool for various purposes, such as editing properties or handling events.
A tentative explanation for the mechanics of introspection would suggest that it primarily revolves around naming conventions as per the JavaBeans standard. For instance, properties are typically exposed through getter and setter methods that adhere to a specific naming pattern, like `getProperty()` or `setProperty(value)`. By scanning for these patterns, introspection mechanisms can deduce the properties of a bean. Furthermore, the JavaBeans API provides two classes that play a pivotal role in introspection: `BeanInfo` and `Introspector`. The `BeanInfo` interface allows bean developers to explicitly control the introspection process by defining which properties, events, and methods are exposed. The `Introspector` class, on the other hand, is used when a bean does not have an associated `BeanInfo` class. It employs reflection to analyze the bean's class and infer its properties, events, and methods.
It's also worth noting that introspection in JavaBeans is not just limited to exposing properties and events; it also extends to understanding the event listeners that a bean supports. This allows tools and applications to interact dynamically with the bean, registering event listeners and responding to events generated by the bean. In summary, introspection in JavaBeans is a mechanism that leverages Java's Reflection API and naming conventions to expose the internal features of JavaBeans, such as properties, events, and methods, enabling tools and applications to interact with these components dynamically and effectively. However, as with any reflection-based technology, it should be used judiciously, considering its impact on performance and security.

After completing the module, you will have the knowledge and skills necessary to:

1. Apply property and event design patterns to support automatic introspection
2. Explicitly provide Bean information in lieu of automatic introspection
3. Build a basic Bean from scratch

In the next lesson, you learn how Beans expose their internal structure and functionality.

When Beans are used by a visual development tool, they have to expose their properties, methods, and events. This allows both the tool and the user to manipulate the Bean's appearance and behavior. We have already seen this when we used BeanBox to work with the simulator Beans: BeanBox allowed us to change property values for the Beans, and to connect event sources with event targets. We didn not have to write any extra code to tell BeanBox about the Bean's properties and events. Instead, it relied on the Java reflection mechanism to gather this information. We have actually been providing all of the necessary information all along by following the design patterns for properties and events when we wrote the code for the Beans. For instance, all of the Beans we have created so far have used

1. getPropertyName() and
2. setPropertyName() methods

for their properties. Remember that this is the pattern for coding a read/write property. Using these patterns allows the Java reflection mechanism to analyze the code and determine that there is a property called PropertyName. Sometimes the information that we provide implicitly using design patterns is not enough, and sometimes the reflection mechanism exposes more information than we want exposed. The reflection mechanism also forces us to follow design patterns that may not make sense all of the time. Finally, we sometimes want to expose information about our Beans that cannot be represented by the standard design patterns.