java Programming in Linux with gcj (basic)

Listing 1. HelloWorld.java

public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, World!");
}
}

The simple Java source code in Listing 1 can be compiled into Java bytecode with gcj -C HelloWorld.java and interpreted using gij HelloWorld. The same source code can be compiled into a native executable using gcj --main=HelloWorld -o HelloWorld HelloWorld.java and executed using ./HelloWorld. This article avoids including import and other trivial statements in Java code listings; see Resources for the full source files.

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## make executable
$ gcj -C HelloWorld.java
$ gij HelloWorld # to test if it works
$ gcj --main=HelloWorld -o HelloWorld HelloWorld.java
$ ./HelloWorld # to run it and test

## make executable jar (same way with in Windows)
$ gcj -c HelloWorld.class          # compile Hello.class to Hello.o
$ jar cvf hi.jar HelloWorld.class  # create a jar
## You got to include "manefest" file containing the class name of the "main()" method as:Main-class: your.package.Class_NAME.without_dot_class
# modify the "MANIFEST.MF", adding at the end: Main-class: HelloWorld # Note: 1) there is a space after ':'. 2) there is NO empty line before the 'Main-class' line.


## make executable with jar
$ gcj -c HelloWorld.class          # compile Hello.class to Hello.o
$ jar cvf hi.jar HelloWorld.class  # create a jar
$ gcj -c hi.jar                    # compile hi.jar to hi.o
$ gcj --main=HelloWorld -o hi hi.o # link hi.o to hi; gcj accept all reasonable input files, such as .java files, .class files and .o files, even .jar files. Super!!!
$ ./hi                             # run hi
Hello, World!