The UnsatisfiedLinkError is thrown if the Java Virtual Machine cannot find an appropriate native-language definition of a method declared native.

In order for System.loadLibrary() to work, the library (on Windows, a DLL) must be in a directory somewhere on your PATH or on a path listed in the java.library.path system property, so you can launch Java like:

java -Djava.library.path=/path/to/dir

Additionally, for loadLibrary(), you specify the base name of the library, without the .dll at the end. So, for /path/to/dir/foo.dll, you would just use:

System.loadLibrary("foo")

You also need to look at the exact UnsatisfiedLinkError that you are getting. If it says something like:

Exception in thread “main” java.lang.UnsatisfiedLinkError: no foo in java.library.path

then it can’t find the foo library (foo.dll) in your PATH or java.library.path specified at launch time.

If it says something like:

Exception in thread “main” java.lang.UnsatisfiedLinkError: com.example.program.ClassName.foo()V

then something is wrong with the library itself in the sense that Java is not able to map a native Java function in your application to its actual native counterpart.

To start with, I would put some logging around your System.loadLibrary() call to see if that executes properly. If it throws an exception or is not in a code path that is actually executed, then you will always get the latter type of UnsatisfiedLinkError explained above.

As a side note, most people put their loadLibrary() calls into a static initializer block in the class with the native methods, to ensure that it is always executed exactly once:

public class Foo {

    static {
        System.loadLibrary("foo");
    }

    public Foo() {}

}

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