Java development kit (JDK)

The Java Development Kit (JDK) from the company Sun bundles a series of command- line oriented tools that are used to create, compile and execute programs in the Java programming language. The JDK also contains extensive libraries, source codes and sample programs, which provide a useful basis for developing your own software. The JDK, which is available for various areas of application, does not include a graphical development environment. In January 2010, the JDK is available in version 6, update 18 under the GNU General Public License( GPL). Likewise, the detailed API and tool documentation is available under the link below.

The JDK does not include its own graphical development environment. However, various manufacturers have developed graphical development environments for Java since its inception. Here for example the comfortable development environments Eclipse and NetBeans (likewise a free SUN product) are to be referred.

Depending on the intended use, the JDK is available for different areas of application.

Standard Edition (J2SE) The Java 2 Standard Edition is used for the development and execution of Java programs for standard applications.

Enterprise Edition (J2EE) The Java 2 Enterprise Edition provides additional libraries for distributed applications and web services.

Micro Edition (Java ME) The Java Micro Edition is intended for applications on compact, portable computers such as PDAs and organizers as well as smartphones. Originally, this edition was implemented with the background of low memory usage and reduced computing power. In the meantime, however, modern devices have considerably more computing power and higher memory, so that a normal Java Virtual Machine( JVM) can also run.

In the following the most important elements of the JDK are listed first.

Java Compiler The Java Compiler javac serves the translation of the Java program. In the process, a platform-independent intermediate code, the so-called bytecode, is generated. This is stored in a file that has the same name as the source code file - but with the file name extension *. class. This bytecode is platform-independent, because it does not differ for the different computer platforms, for example Windows, Solaris or Linux. However, this intermediate code is also not directly executable on the target system.

Java Interpreter The Java Interpreter java realizes the execution of the byte code produced by the compiler and is thus platform-dependent. There are thus for many platforms appropriate interpreters. A Java interpreter is also called Java Virtual Machine (JVM).

Java Archiver The jar ( Java archive) utility is available from the command line and implements various options to create archives, extract them and view them. However, with the libraries provided in the JDK, there is also an Application Programming Interface (API) with which everything can be programmed in the same way as the utility itself does. The advantage of bundling in an archive is that developers can conveniently bundle their class and source code files into a single executable. Another consideration is that operating systems such as Windows and Mac OS X have the Java Runtime Environment( JRE) associated with the .jar file extension by default, so double-clicking on a jar file starts the program right away.

Java Documentation The Java tool javadoc generates an external HTML file for each public class based on special documentation comments in the Java source code. In addition, further information such as an overview of all classes, exceptions, methods and interfaces are generated in a separate file. In doing so, javadoc strictly observes the aspect of visibility, which is important in the object-oriented world, and by default only includes public things in the documentation.

Monitoring programs Under it since the versions Java 5 and Java 6 programs are summarized, which list started Java programs and make possible purposeful inquiries to these at the run time. In detail these are the tools:

• Java Virtual Machine Process Status Tool (jps) supplies all running Java programs,
• Java Virtual Machine Statistics Monitoring Tool (jstat) provides performance statistics,
• Java Memory Map (jmap) lists all copies of Java objects and the memory they occupy, and
• stack trace tool (jstack) can be used to display running threads along with information about the wait state enforced by monitors.

In addition, an extensive collection of libraries, components and sample programs is provided when downloading the JDK.