The Java TM Tutorial

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Trail: Getting Started
Lesson: The Java Phenomenon

## What Can Java Do?

> Probably the most well-known Java programs are Java applets. An applet is a Java program that adheres to certain conventions that allow it to run within a Java-enabled browser. At the beginning of this trail is an applet that displays an animation of Java's mascot, Duke, waving at you.

> However, Java is not just for writing cute, entertaining applets for the World Wide Web ("Web"). Java is a general-purpose, high-level programming language and a powerful software platform. Using the generous Java API, you can write many types of programs.

> The most common types of programs are probably applets and applications, where a Java 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 include Web servers, proxy servers, mail servers, print servers, and boot servers. Another specialized program is a servlet. Servlets are similar to applets in that they are runtime extensions of applications. Instead of working in browsers, though, servlets run within Java servers, configuring or tailoring the server.

> How does the Java API support all of these kinds of programs? With packages of software components that provide a wide range of functionality. The core API is the API included in every full implementation of the Java platform. The core API 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 Java applets.
> - Networking: URLs, TCP and UDP sockets, and IP 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/private key management, access control, and certificates.
> - Software components: Known as JavaBeans, can plug into existing component architectures such as Microsoft's OLE/COM/Active-X architecture, OpenDoc, and Netscape's Live Connect.
> - Object serialization: Allows lightweight persistence and communication via Remote Method Invocation (RMI).
> - Java Database Connectivity (JDBC): Provides uniform access to a wide range of relational databases.
> Java not only has a core API, but also standard extensions. The standard extensions define APIs for 3D, servers, collaboration, telephony, speech, animation, and more.

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