Oracles Java Virtual Machine

Oracle ˜s Java Virtual Machine

Sun Microsystems furnishes the Java Compatibility Kit (JCK) to allow JVM vendors to ensure that their implementations meet the requirements for how the JVM compiles the bytecodes into native machine code. The Oracle Database and Application Server both contain the Oracle JVM, which Oracle has fully tested with the JCK.

The Oracle Database 10 g Release 1 (10.1) includes version 1.4.1 of the Java Standard Edition platform, also known as the Enterprise Java Engine (EJE).

Note  

Oracle 8i uses the 1.2 of the JVM; Oracle 9i uses 1.3 of the JVM.

The Oracle10 g Application Server (9.0.4) includes version 1.3 of the Java Enterprise Edition platform. There is no way to change the version of the JVM other than upgrading to a new version of Oracle or applying an Oracle-supplied patch, if a patch is available. When developing Java programs that execute using the JVM in the database or the application server, you should use a version of the Java development platform that is the same or older than the version of the Oracle JVM.

Three major differences between the Oracle JVM and a typical client JVM are

• main() method . As shown in the previous examples, a standalone Java application, as with a C program, must contain a single method named main() that is the entry point to the application. Java programs within the database are not standalone applications; rather they are just methods that you can execute individually. Therefore, no main() method is required.

• Graphical user interface (GUI) . The Oracle 10 g Database supports the headless Abstract Windowing Toolkit (AWT). The Oracle JVM now includes the AWT classes, and your programs can manipulate graphical objects, such as using fonts and preparing printouts, as long as the programs do not attempt to display the GUI on the database server. For security reasons, the Oracle JVM cannot interact with the display and input hardware on the server where the Oracle Database is running.

• The Java language allows applications to create multiple threads to increase scalability . Developing multithreaded applications introduces another level of complexity, as the operating system is free to swap threads in and out of main memory as needed, which can lead to unexpected variable values if not properly controlled. One of the advantages of using the Oracle JVM is that the task scheduler built within the RDBMS efficiently handles thousands of simultaneous connections, and therefore provides for scalability without the use of multiple threads. Coding multiple-threaded applications in database programs does not increase scalability, and may hurt performance as the garbage collection process is less efficient.

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