Implementing Native Methods

The Example

The example implements a simple "character-replace" program. You invoke the program with these command line arguments:

char1 char2 inputfile outputfile

The Replace program reads from inputfile, replaces all occurrences of char1 with char2, and writes the results to outputfile.

The Source Files

Replace.java

Contains the main program.

File.java

Defines the File class. This class provides basic file and path manipulation with the expectation that subclasses will provide the actual file management code depending on the file semantics they want to present. InputFile and OutputFile both derive from File.

InputFile.java

Contains the InputFile class (a subclass of File) that implements a read-only input file. This class declares three native methods whose implementations are written in the C programming language and provided in InputFileImpl.c.

OutputFile.java

Contains the OutputFile class (a subclass of File) that implements a write-only output file. This class declares three native methods whose implementations are written in the C programming language and provided in OutputFileImpl.c.

Files Generated by javah

File.h

InputFile.h

OutputFile.h

C header files generated by javah.

File.c

InputFile.c

OutputFile.c

C stub files generated by javah -stubs.

Instructions

1. Compile the .java files into .class files using the Java compiler
2. Compile all of the C code into a dynamically loadable library named "file". If you don't know how to do this, follow the instructions in Step 6: Create a Dynamically Loadable Libraryin the Step By Step lesson.
3. Run the program using the Java interpreter.

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