Java Cookbook

Blending in Native Code (C/C++)

Problem

You wish to call native C/C++ functions from Java, either for efficiency or to access hardware- or system-specific features.

Solution

Use JNI, the Java Native Interface.

Discussion

Java lets you load native or compiled code into your Java program. Why would you want to do such a thing? One reason might be to access OS-dependent functionality. Another is speed: native code will likely run faster than Java, at least at present. Like everything else in Java, this mechanism is subject to security restrictions; for example, applets are not allowed to access native code.

The native code language bindings are defined for code that has been written in the C or C++ language. If you need to access a language other than C/C++, write a bit of C/C++ and have it pass control to other functions or applications, using any mechanism defined by your operating system.

Due to such system-dependent features as the interpretation of header files and the allocation of the processor’s general-purpose registers, your native code may need to be compiled by the same C compiler used to compile the Java runtime for your platform. For example, on Solaris you can use SunPro C, or maybe gcc. On Win32 platforms, use Microsoft Visual C++ Version 4.x or higher (32 bit). For other platforms, see your Java vendor’s documentation.

Also note that the details in this section are for Java 1.1’s Java Native Interface (JNI) that differs in some details from 1.0 and from Microsoft’s native ...