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Lesson 1

Introduction to Distributed Applications and Components

In order that you fully understand how to write Enterprise JavaBeans (EJBs), it is important that you understand where they reside.
In this module, I will create a map of the world in which distributed objects and constructors provide useful services to client programs.
This introduction will let you find your way within the technology that is introduced in the rest of the course.

Understanding the Territory

I will explain how a client program communicates with a remote object , and how it makes use of the services it provides. I will identify the properties of a reusable component, and describe how they can be connected together so that you can build flexible applications.
I will explain the function of servers, containers, and Object Monitors (OMs). You will be introduced to transactions within this world of distributed objects. You will learn about the deployment of remote objects and how they get information about local resources , such as the names of the local databases.
Carefully read this section in preparation for the tutorial on Enterprise Java Beans. The information in this section is the foundation for all that follows.

  1. Message: Another name for a method call. Conveys the idea that the method call is invoked across a network.
  2. Distributed object: An object somewhere on the network that provides some service that is known and available to clients.
  3. constructor:A pseudo-method that creates an object.
  4. Remote object: An object that provides a service through its methods and is located on another host on the network. The location ofthe object needs to be known before its methods can be called.
  5. Component: A physical and replaceable part of a system that conforms to and provides a realization of a set of interfaces.
  6. Object monitor: The combination of remote object together with the environment that manages it and that allows method calls to the remote object.
  7. Local resource: A resource, such as a database connection, that is accessible without traversing the network.
In the next lesson, clients and remote objects will be introduced.