How Java Changed the Internet
The Internet helped catapult Java to the forefront of programming, and Java, in turn, had
a profound effect on the Internet. In addition to simplifying web programming in general,
Java innovated a new type of networked program called the applet that changed the way
the online world thought about content. Java also addressed some of the thorniest issues
associated with the Internet: portability and security. Let’s look more closely at each of these.
Java Applets
An applet is a special kind of Java program that is designed to be transmitted over the Internet
and automatically executed by a Java-compatible web browser. Furthermore, an applet is
downloaded on demand, without further interaction with the user. If the user clicks a link
that contains an applet, the applet will be automatically downloaded and run in the browser.
Applets are intended to be small programs. They are typically used to display data provided
by the server, handle user input, or provide simple functions, such as a loan calculator, that
execute locally, rather than on the server. In essence, the applet allows some functionality to
be moved from the server to the client.
The creation of the applet changed Internet programming because it expanded the
universe of objects that can move about freely in cyberspace. In general, there are two very
broad categories of objects that are transmitted between the server and the client: passive
information and dynamic, active programs. For example, when you read your e-mail, you
are viewing passive data. Even when you download a program, the program’s code is still
only passive data until you execute it. By contrast, the applet is a dynamic, self-executing
program. Such a program is an active agent on the client computer, yet it is initiated by
the server.
As desirable as dynamic, networked programs are, they also present serious problems
in the areas of security and portability. Obviously, a program that downloads and executes
automatically on the client computer must be prevented from doing harm. It must also be
able to run in a variety of different environments and under different operating systems.
As you will see, Java solved these problems in an effective and elegant way. Let’s look a bit
more closely at each.
Security
As you are likely aware, every time you download a “normal” program, you are taking a risk,
because the code you are downloading might contain a virus, Trojan horse, or other harmful
code. At the core of the problem is the fact that malicious code can cause its damage because
it has gained unauthorized access to system resources. For example, a virus program might
gather private information, such as credit card numbers, bank account balances, and
passwords, by searching the contents of your computer’s local file system. In order for Java to
enable applets to be downloaded and executed on the client computer safely, it was necessary
to prevent an applet from launching such an attack.
Java achieved this protection by confining an applet to the Java execution environment
and not allowing it access to other parts of the computer. (You will see how this is
accomplished shortly.) The ability to download applets with confidence that no harm will
be done and that no security will be breached may have been the single most innovative
aspect of Java.
Portability
Portability is a major aspect of the Internet because there are many different types of
computers and operating systems connected to it. If a Java program were to be run on
virtually any computer connected to the Internet, there needed to be some way to enable
that program to execute on different systems. For example, in the case of an applet, the
same applet must be able to be downloaded and executed by the wide variety of CPUs,
operating systems, and browsers connected to the Internet. It is not practical to have
different versions of the applet for different computers. The same code must work on all
computers. Therefore, some means of generating portable executable code was needed. As
you will soon see, the same mechanism that helps ensure security also helps create portability.
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