For many years, the Java Platform, Enterprise Edition (formerly known as J2EE) was a de facto standard for large-scale enterprise applications. Originally developed by Sun Microsystems and now owned by Oracle, it lends itself to multitiered and load-balanced architectures and is well suited to modular development and code reuse. Because of its long history and widespread adoption, many high-quality development tools, application servers, and frameworks are available to assist developers.
James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991. Java was originally designed for interactive television, but it was too advanced for the digital cable television industry at the time. The language was initially called Oak after an oak tree that stood outside Gosling’s office. Later the project went by the name Green and was finally renamed Java, from Java coffee, the coffee from Indonesia. Gosling designed Java with a C/C++-style syntax that system and application programmers would find familiar.
There were five primary goals in the creation of the Java language:
- It must be simple, object-oriented, and familiar.
- It must be robust and secure.
- It must be architecture-neutral and portable.
- It must execute with high performance.
- It must be interpreted, threaded, and dynamic.
As of September 2020, Java 8 and 11 are supported as Long Term Support (LTS) versions, and one later non-LTS version is supported.Major release versions of Java, along with their release dates:
|JDK1.0||January 23, 1996|
|JDK 1.1||February 19, 1997|
|J2SE 1.2||December 8, 1998|
|J2SE 1.3||May 8, 2000|
|J2SE 1.4||February 6, 2002|
|J2SE 5.0||September 30, 2004|
|Java SE 6||December 11, 2006|
|Java SE 7||July 28, 2011|
|Java SE 8||March 18, 2014|
|Java SE 9||September 21, 2017|
|Java SE 10||March 20, 2018|
|Java SE 11||September 25, 2018|
|Java SE 12||March 19, 2019|
|Java SE 13||September 17, 2019|
|Java SE 14||March 17, 2020|
|Java SE 15||September 15, 2020|
The Java Platform can be run on several underlying operating systems, including Windows, Linux, and Solaris. Descriptions of Java-based web applications often employ a number of potentially confusing terms that you may need to be aware of:
- An Enterprise Java Bean (EJB) is a relatively heavyweight software component that encapsulates the logic of a speciﬁ c business function within the application. EJBs are intended to take care of various technical challenges that application developers must address, such as transactional integrity.
- A Plain Old Java Object (POJO) is an ordinary Java object, as distinct from a special object such as an EJB. A POJO normally is used to denote objects that are user-deﬁ ned and are much simpler and more lightweight than EJBs and those used in other frameworks.
- Java Servlet is an object that resides on an application server and receives HTTP requests from clients and returns HTTP responses. Servlet implementations can use numerous interfaces to facilitate the development of useful applications.
- A Java web container is a platform or engine that provides a runtime environment for Java-based web applications. Examples of Java web containers are Apache Tomcat, BEA WebLogic, and JBoss. Many Java web applications employ third-party and open source components alongside custom-built code. This is an attractive option because it reduces development effort, and Java is well suited to this modular approach.
- Applet : Java applets were programs that were embedded in other applications, typically in a Web page displayed in a web browser. The Java applet API is now deprecated since Java 8 in 2017.
- JavaServer Pages: JavaServer Pages (JSP) are server-side Java EE components that generate responses, typically HTML pages, to HTTP requests from clients. JSPs embed Java code in an HTML page by using the special delimiters <% and %>. A JSP is compiled to a Java servlet, a Java application in its own right, the first time it is accessed. After that, the generated servlet creates the response.
- Swing application: Swing is a graphical user interface library for the Java SE platform. It is possible to specify a different look and feel through the pluggable look and feel system of Swing. Clones of Windows, GTK+, and Motif are supplied by Sun. Apple also provides an Aqua look and feel for macOS. Where prior implementations of these looks and feels may have been considered lacking, Swing in Java SE 6 addresses this problem by using more native GUI widget drawing routines of the underlying platforms.
- JavaFX application: JavaFX is a software platform for creating and delivering desktop applications, as well as rich Internet applications (RIAs) that can run across a wide variety of devices. JavaFX is intended to replace Swing as the standard GUI library for Java SE, but since JDK 11 JavaFX has not been in the core JDK and instead in a separate module. JavaFX has support for desktop computers and web browsers on Microsoft Windows, Linux, and macOS. JavaFX does not have support for native OS look and feels.
- Generics : In 2004, generics were added to the Java language, as part of J2SE 5.0. Prior to the introduction of generics, each variable declaration had to be of a specific type. For container classes, for example, this is a problem because there is no easy way to create a container that accepts only specific types of objects. Either the container operates on all subtypes of a class or interface, usually Object, or a different container class has to be created for each contained class. Generics allow compile-time type checking without having to create many container classes, each containing almost identical code. In addition to enabling more efficient code, certain runtime exceptions are prevented from occurring, by issuing compile-time errors. If Java prevented all runtime type errors (ClassCastExceptions) from occurring, it would be type safe. In 2016, the type system of Java was proven unsound.
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