gcj - Unix, Linux Command



gcj - Ahead-of-time compiler for the Java language


gcj [-Idir...] [-d dir...]
[--CLASSPATH=path] [--classpath=path]
[-foption...] [--encoding=name]
[--main=classname] [-Dname[=value]...]
[-C] [--resource resource-name] [-d directory]
sourcefile ...


The gccmakedep program calls ’gcc -M’ to output makefile rules describing the dependencies of each sourcefile, so that make(1) knows which object files must be recompiled when a dependency has changed.

By default, gccmakedep places its output in the file named makefile if it exists, otherwise Makefile. An alternate makefile may be specified with the -f option. It first searches the makefile for a line beginning with


or one provided with the -s option, as a delimiter for the dependency output. If it finds it, it will delete everything following this up to the end of the makefile and put the output after this line. If it doesn’t find it, the program will append the string to the makefile and place the output after that.


Normally, gccmakedep will be used in a makefile target so that typing ’make depend’ will bring the dependencies up to date for the makefile. For example,
    SRCS = file1.c file2.c ...
    CFLAGS = -O -DHACK -I../foobar -xyz
            gccmakedep -- $(CFLAGS) -- $(SRCS)


The program will ignore any option that it does not understand, so you may use the same arguments that you would for gcc(1), including -D and -U options to define and undefine symbols and -I to set the include path.
-a Append the dependencies to the file instead of replacing existing dependencies.
  Filename. This allows you to specify an alternate makefile in which gccmakedep can place its output. Specifying \(lq-\(rq as the file name (that is, -f-) sends the output to standard output instead of modifying an existing file.
  Starting string delimiter. This option permits you to specify a different string for gccmakedep to look for in the makefile. The default is \(lq# DO NOT DELETE\(rq.
-- options --
  If gccmakedep encounters a double hyphen (--) in the argument list, then any unrecognized arguments following it will be silently ignored. A second double hyphen terminates this special treatment. In this way, gccmakedep can be made to safely ignore esoteric compiler arguments that might normally be found in a CFLAGS make macro (see the EXAMPLE section above). -D, -I, and -U options appearing between the pair of double hyphens are still processed normally.


gcj compiles java code into native code instead of bytecode.

Consider the class file HelloWorld.java.
import java.lang.String;
public class HelloWorld
    public static void main(String[] args)
        System.out.println("Hello World...!");

Compile the above .java file using gcj
$ gcj -o HelloWorld --main=HelloWorld HelloWorld.java

Above command will create a executable file HelloWorld

Run the executable as below
$ ./HelloWorld
Hello World...!

In the absence of -o option the an executable file a.out will be created. In java is it common to have multiple classes with main method. So it is required to tell the linker the which main method to be used when program starts. This is done using --main=ClassName

Generating bytecode
$ gcj -C --main=HelloWorld HelloWorld.java
Above command will create class file HelloWorld.class