What is Java on z/OS?

[Anuj Dhawan]

Java™ is an object-oriented programming language developed by Sun Microsystems, Inc. Java can be used for developing traditional mainframe commercial applications as well as Internet and intranet applications that use standard interfaces.

Java is an increasingly popular programming language used for many applications across multiple operating systems. IBM® is a major supporter and user of Java across all of the IBM computing platforms, including z/OS®. The z/OS Java products provide the same, full function Java APIs as on all other IBM platforms. In addition, the z/OS Java licensed programs have been enhanced to allow Java access to z/OS unique file systems. Programming languages such as Enterprise COBOL and Enterprise PL/I in z/OS provide interfaces to programs written in Java. These languages provide a set of interfaces or facilities for interacting with programs written in Java.

The various Java Software Development Kit (SDK) licensed programs for z/OS help application developers use the Java APIs for z/OS, write or run applications across multiple platforms, or use Java to access data that resides on the mainframe. Some of these products allow Java applications to run in only a 31-bit addressing environment. However, with 64-bit SDKs for z/OS, pure Java applications that were previously storage-constrained by 31-bit addressing can execute in a 64-bit environment. Also, some mainframes support a special processor for running Java applications called the zSeries® Application Assist Processor (zAAP). Programs can be run interactively through z/OS UNIX® or in batch.

IBM SDK products for z/OS
As with Java SDKs for other IBM platforms, z/OS Java SDK licensed programs are supplied for industry standard APIs. The z/OS SDK products are independent of each other and can be ordered and serviced separately.

The Java Native Interface (JNI)
The Java Native Interface (JNI) is the Java interface to native programming languages and is part of the Java Development Kits. If the standard Java APIs do not have the function you need, the JNI allows Java code that runs within a Java Virtual Machine (JVM) to operate with applications and libraries written in other languages, such as PL/I. In addition, the Invocation API allows you to embed a Java Virtual Machine into your native PL/I applications.

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