The Java^TM platform is relatively new, which means there could be times when you will need to integrate programs written with the Java language with existing non-Java language services, API toolkits, and programs. The Java platform provides the Java Native Interface (JNI) to help ease this type of integration.

The JNI defines a standard naming and calling convention so the Java¹ virtual machine can locate and invoke native methods. In fact, JNI is built into the Java virtual machine so the Java virtual machine can invoke local system calls to perform input and output, graphics, networking, and threading operations on the host operating system.

This chapter explains how to use JNI in programs written in the Java language to call any libraries on the local machine, call Java language methods from inside native code, and how to create and run a Java VM instance. To show how you can put JNI to use, the examples in this chapter include integrating JNI with the Xbase C++ database API, and how you can call a mathematic function. Xbase has sources you can download.

• JNI Example
• Strings and Arrays
• Other Programming Issues

In a Rush?

Topic	Section
JNI Example	About the Example Generate the Header File Method Signature Implement the Native Method Compile the Dynamic or Shared Object Library Run the Example
Strings, Arrays, and Fields	Passing Strings Passing Arrays Pinning Array Object Arrays Multi-Dimensional Arrays Accessing Fields
Other Programming Issues	Language Issues Calling Methods Accessing Fields Threads and Synchronization Memory Issues Invocation Attaching Threads

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¹ As used on this web site, the terms "Java virtual machine" or "JVM" mean a virtual machine for the Java platform.