jnr-ffi is a Java library for loading native libraries without writing JNI code by hand, or using tools such as SWIG.

package helloworld;

import jnr.ffi.LibraryLoader;

public class HelloWorld {
    public static interface LibC {
        int puts(String s);
    }

    public static void main(String[] args) {
        LibC libc = LibraryLoader.create(LibC.class).load("c");

        libc.puts("Hello, World");
    }
}

All Java primitives are mapped simply to the equivalent C types.

• byte - 8 bit signed integer
• short - 16 bit signed integer
• int - 32 bit signed integer
• long - natural long (i.e. 32 bits wide on 32-bit systems, 64 bits wide on 64-bit systems)
• float - 32 bit float
• double - 64 bit float

The width and/or signed-ness of these basic types can be specified using one of the type alias annotations. e.g.

// Use the correct width for the result from getpid(3)
@pid_t long getpid();

// read(2) returns a signed long result, and its length parameter is an unsigned long
@ssize_t long read(int fd, Pointer data, @size_t long len);

In addition, the following Java types are mapped to a C pointer

• String - equivalent to const char *
• Pointer - equivalent to void *
• Buffer - equivalent to void *