How does jni work

The JVM is guaranteed to pass the same interface pointer to a native method when it makes multiple calls to the native method from the same Java thread. However, a native method can be called from different Java threads, and therefore may receive different JNI interface pointers. Native methods are loaded with the System. In the following example, the class initialization method loads a platform-specific native library in which the native method f is defined:. The argument to System. The system follows a standard, platform-specific approach to convert the library name to a native library name.

Dynamic linkers resolve entries based on their names. Primitive types, such as integers, characters, and so on, are copied between Java and native code. Arbitrary Java objects, on the other hand, are passed by reference. This table shows the mapping of types between Java and native code. These types are interchangeable. We use the JDK javah utility to generate the header file Hello.

We then create Hello. Compiling We are now ready to compile our program and run it. The compilation is system-dependent. This will create libHelloImpl. Programmers use the JNI to write native methods to handle those situations when an application cannot be written entirely in the Java programming language. For example, you may need to use native methods and the JNI in the following situations: The standard Java class library may not support the platform-dependent features needed by your application.

You may already have a library or application written in another programming language and you wish to make it accessible to Java applications. You may want to implement a small portion of time-critical code in a lower-level programming language, such as assembly, and then have your Java application call these functions.

Programming through the JNI framework lets you use native methods to do many operations. Native methods may represent legacy applications or they may be written explicitly to solve a problem that is best handled outside of the Java programming environment. Collectives on Stack Overflow. Learn more. Asked 4 years, 4 months ago. Active 1 year, 1 month ago.

Viewed times. Improve this question. Urvashi Sharma Urvashi Sharma 13 1 1 bronze badge. Add a comment. Active Oldest Votes. Improve this answer. Thank you for your answer. It does help. This Java program prints the values of CPU usage coming from.