The most common types of programs
written in the Java programming language are applets
and applications.
If you’ve surfed the Web, you’re probably already familiar with applets. An
applet is a program that adheres to certain conventions that allow it to run
within a Java-enabled browser.
However, the Java programming
language is not just for writing cute, entertaining applets for the Web. The
general-purpose, high-level Java programming language is also a powerful
software platform. Using the generous API, you can write many types of
programs.
An application is a standalone
program that runs directly on the Java platform. A special kind of application
known as a server
serves and supports clients on a network. Examples of servers are Web servers,
proxy servers, mail servers, and print servers. Another specialized program is
a servlet. A
servlet can almost be thought of as an applet that runs on the server side.
Java Servlets are a popular choice for building interactive web applications,
replacing the use of CGI scripts. Servlets are similar to applets in that they
are runtime extensions of applications. Instead of working in browsers, though,
servlets run within Java Web servers, configuring or tailoring the server.
How does the API support all these
kinds of programs? It does so with packages of software components that
provides a wide range of functionality. Every full implementation of the Java
platform gives you the following features:
·
The
essentials:
Objects, strings, threads, numbers, input and output, data structures, system
properties, date and time, and so on.
·
Applets: The set of conventions used by
applets.
·
Networking: URLs, TCP (Transmission Control
Protocol), UDP (User Data gram Protocol) sockets, and IP (Internet Protocol)
addresses.
·
Internationalization: Help for writing programs that can
be localized for users worldwide. Programs can automatically adapt to specific
locales and be displayed in the appropriate language.
·
Security: Both low level and high level,
including electronic signatures, public and private key management, access
control, and certificates.
·
Software
components:
Known as JavaBeansTM, can plug into existing component
architectures.
·
Object
serialization:
Allows lightweight persistence and communication via Remote Method Invocation
(RMI).
·
Java
Database Connectivity (JDBCTM): Provides uniform access to a wide
range of relational databases.
The Java platform also has APIs for
2D and 3D graphics, accessibility, servers, collaboration, telephony, speech,
animation, and more. The following figure depicts what is included in the Java
2 SDK.
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