This document discusses distributed computing and some of its implications. It begins by introducing concepts like network programming, mobile programming, and component-based programming that arise from relaxing the rules of object-oriented programming to allow objects to reside on different machines. The document then focuses on client-server computing, describing how Java simplifies building client-server systems through libraries for addressing, ports, sockets, and streams. It also discusses general servers that can accept connections from many clients simultaneously and object serialization for transferring objects across networks.

1. Distributed Computing
DISTRIBUTED COMPUTING
Muhammad Adil Raja
Roaming Researchers, Inc.
cbna
April 24, 2015

2. Distributed Computing
OUTLINE I
1 INTRODUCTION
2 REFERENCES

3. Distributed Computing
Introduction
INTRODUCTION
In this chapter we will explore some of the implications of
programming in a distributed environment.
Network programming.
Mobile programming.
Component based programming.

4. Distributed Computing
Introduction
AN OBJECT ORIENTED COMMUNITY
Recall that we have been asserting that an object-oriented
program is properly thought of as a member of a
community.
If we relax the rules for membership in this community, we
move the paradigm in different directions.

5. Distributed Computing
Introduction
RELAXING THE RULES
What are some of the ways we can relax the rules?
Allowing objects to be written in different languages –
(corba, dcom).
Allowing objects on the same machine to form connections
dynamically – (java beans).
Allowing objects to reside on different computers –
(distributed computing).
Allowing objects on different computers to form
connections dynamically – (mobile computing).
All of these are conceptually easy, but the devil is in the
details.

6. Distributed Computing
Client-Server Computing
CLIENT-SERVER COMPUTING
The simplest type of interaction is allowing objects to
reside on different computers, but with known interfaces.
This is termed client/server computing.
The book describes a simple client/server system.

7. Distributed Computing
Client-Server Computing
MAKING IT EASIER TO WRITE CLIENT-SERVER
SYSTEMS
Java simplifies the production of client/server systems by
providing ready-made library routines for:
Address – IP addresses or domain names.
Ports – an address in a computer for creating connections.
Sockets – a connection between one computer and an
address/port on another computer.
Streams – for reading from and writing to a socket.
Doesn’t mean it can’t be done in other languages, but Java
makes it a lot easier since they have spent a lot of time
giving you simple interfaces for these activities.

8. Distributed Computing
Client-Server Computing
NEXT LEVEL OF COMPLEXITY
The next level of complexity is a general server who is
ready to accept connections from many clients, perhaps
many at one time.
The book describes a system for this.

9. Distributed Computing
Client-Server Computing
OBJECT SPECIALIZATION
Another useful feature (which should perhaps have been
described in the metaprogramming chapter) is the ability to
transfer objects across a network connection and
regenerate them on the far side.
Called object serialization, sometimes marshalling.
Again, Java has a nice facility for this. Other langauges
may as well, but I’m less familiar with them.
The book gives an example of object serialization.

10. Distributed Computing
Client-Server Computing
ASKING AN OBJECT ABOUT ITS STATE
Moving back to a single machine, there are systems that
allow a program to dynamically inquire the capabilities of
another class, and then add it into a running program.
A good example is Java Beans, which is not described in
the book.
Again, this is built on the reflection facilities described in
the previous chapter.
The programmer collects a bunch of components, then
assembles them into a new application.
Often components have a visual interface, and can be
assembled using a visual tool, without needing to write
(much) programming.

11. Distributed Computing
Client-Server Computing
ACROSS A NETWORK
The next level of complexity is to do the same sort of thing,
but allow the components to exist across the network.
This is part of what MS is trying to do with its dot-net
program.
Allow the creation of components which can then be
assembled even when they exist on widely separated
computers.
Many parts of this problem:
Registration – how do you find out what components exist
out there?
Interface Query – how do you find out what interfaces
these components use
Connection – how do you make a dynamic connection with
a remote object
Interaction – how do you communicate with a remote

12. Distributed Computing
Client-Server Computing
THE FUTURE
I expect that in three years time this chapter will be a lot
richer and a lot thicker.
There is an awful lot of work going on in this area right now.
Some of these ideas will be successful and continue, some
will die out and be replaced.
You should expect to be hearing more about distributing /
network / web based computing as time goes on.

13. Distributed Computing
References
REFERENCES
Images and content for developing these slides have been
taken from the follwoing book with the permission of the
author.
An Introduction to Object Oriented Programming, Timothy
A. Budd.
This presentation is developed with Beamer:
JuanLesPins, monarca.