javah

You use the javah tool to generate C header and source files from a Java class.

Note:

The javah tool is deprecated as of JDK 9 and might be removed in a future JDK release. The tool has been superseded by the -h option added to javac in JDK 8.

Synopsis

javah [options] fully-qualified-class-name ...

options

Specifies the command-line options. See Options for javah.

fully-qualified-class-name

Specifies the fully qualified location of the classes to be converted to C header and source files.

Each class must be specified by its fully qualified name, optionally prefixed by a module name followed by the slash (/). For example:

java.lang.Object

java.base/java.io.File

Description

The javah command generates C header and source files that are needed to implement native methods. The generated header and source files are used by C programs to reference an object's instance variables from native source code. The .h file contains a struct definition with a layout that parallels the layout of the corresponding class. The fields in the struct correspond to instance variables in the class.

The name of the header file and the structure declared within it are derived from the name of the class. When the class passed to the javah command is inside a package, the package name is added to the beginning of both the header file name and the structure name. Underscores (_) are used as name delimiters.

By default, the javah command creates a header file for each class listed on the command line and puts the files in the current directory. Use the -stubs option to create source files. Use the -o option to concatenate the results for all listed classes into a single file.

The Java Native Interface (JNI) doesn’t require header information or stub files. The javah command can still be used to generate native method function prototypes needed for JNI-style native methods. The javah command produces JNI-style output and places the result in the .h file.

Options for javah

Note:

In tools that support -- style options, the GNU-style options can use the equal sign (=) instead of a white space to separate the name of an option from its value.

-o outputfile

Concatenates the resulting header or source files for all the classes listed on the command line into an output file. Only one of the options -o or -d can be used.

-d directory

Sets the directory where the javah command saves the header files or the stub files. Only one of the options -d or -o can be used.

-v or -verbose

Indicates verbose output and causes the javah command to print a message to stdout about the status of the generated files.

-h , -help, or -?

Prints a help message for javah usage.

-version

Prints javah command release information.

-jni

Causes the javah command to create an output file containing JNI-style native method function prototypes. This is the default output; use of -jni is optional.

-force

Specifies that output files should always be written.

--module-path path

Specifies the path from which to load application modules.

--system jdk

Specifies where to find system modules.

--class-path path , -classpath path , or -cp path

Specifies the path that the javah command uses to look up classes. Overrides the default or the CLASSPATH environment variable when it’s set. Directories are separated by colons on Oracle Solaris and semicolons on Windows. The general format for the path is:

• Oracle Solaris, Linux, and OS X:

  :your-path

  Example: :/home/avh/classes:/usr/local/java/classes

• Windows:

  ;your-path

  Example: ;C:\users\dac\classes;C:\tools\java\classes

As a special convenience, a class path element that contains a base name with an asterisk (*) is considered equivalent to specifying a list of all the files in the directory with the extension .jar or .JAR.

For example, if directory mydir contains a.jar and b.JAR, then the class path element mydir/* is expanded to a.jar:b.JAR, except that the order of JAR files is unspecified. All JAR files in the specified directory, including hidden ones, are included in the list. A class path entry that consists of an asterisk (*) expands to a list of all the JAR files in the current directory. The CLASSPATH environment variable, where defined, is similarly expanded. Any class path wildcard expansion occurs before the Java Virtual Machine (JVM) is started. A Java program never sees unexpanded wild cards except by querying the environment, for example, by calling System.getenv("CLASSPATH").

-bootclasspath path

Specifies the path from which to load bootstrap classes.