This simple application will consist of two classes:

We'll package both classes together into a single Smalltalk/X package named jv:demos/helloworld_1.

Before we start, we have to initialize STX:LIBJAVA. For details, refer to Section 1.3, “Initializing Java”, for now, just execute in workspace:

JavaVM boot.

Once the STX:LIBJAVA is booted, create a Java class. In a class browser, select Class → New → Java Class. In the browser's code pane, a template of Java class definition appears. In our case, the new class's source code may look like:

Once you accept the code, the Java class is compiled and loaded into a running system. Now you should be able to use it from a workspace. Open one and evaluate:

helloworld := JAVA jv demos helloworld_1 core HelloWorld new.
helloworld greet.

The first line instantiates the HelloWorld class from Smalltalk. You may alternatively instantiate it as follows:

helloworld := (Java classForName:'jv. demos.helloworld_1.core.HelloWorld') new.

The second line invokes the greet() method. You may also invoke the greet(String) method as simply as:

helloworld greet: 'Haya'.

Now let's define an application startup class:

StandaloneStartup subclass:#HelloWorldStartup
        instanceVariableNames:''
        classVariableNames:''
        poolDictionaries:''
        category:'Hello World'

And it's #main: method - this is the application entry point:

main:argv
    | helloworld |
    JavaVM booted ifFalse:[
        JavaVM boot.
    ].
    helloworld := JAVA jv demos helloworld_1 core HelloWorld new.
    helloworld greet.
    Smalltalk isStandAloneApp ifTrue:[
        Smalltalk exit: 0
    ].

Don't forget to move class HelloWorldStartup to package jv:demos/helloworld_1 (menu Class → Move → To Package).

The initialal code has been developed so now it's time to commit it to Mercurial repository. If you're not familiar with Mercurial under Smalltalk/X, you may want to read stx:libscm User Guide. In the following text, let's assume the Mercurial repository for the package is located at /home/user/SmalltalkXProjects/jv/demos/helloworld_1 (or C:\Users\user\SmalltalkXProjects\jv\demos\helloworld_1 on Windows)

To commit the package, switch browser to package mode (menu View → Package) and commit (menu Package → Mercurial+ → Checkin...).

Commiting package from Smalltalk/x class browser

If the menu item Mercurial+ does not show the text "(default)" then something is wrong with the Mercurial setup - check stx:libscm User Guide.

Once the commit dialog appears, fill in the commit message and click to Commit button.

Commit dialog to commit a package

Now the code has been commited to the repository. Let's check it from command line:

$ cd /home/user/SmalltalkXProjects/jv/demos/helloworld_1
$ hg log
changeset:   0:2fc9b3286e10
tag:         tip
user:        Jan Vrany <jan.vrany@fit.cvut.cz>
date:        Sun Jun 14 08:14:54 2015 +0100
summary:     First shot on a cool "Hello World!" app

$

Before loading the package into freshly started Smalltalk/X IDE you have to manually update Mercurial working copy to desired revision. When a package is commited from Smalltalk/X, the working copy in Smalltalk/X package path is not updated to the commited revision^[2]. So you have to update the working copy by hand:

$ cd /home/user/SmalltalkXProjects/jv/demos/helloworld_1
$ hg up
17 files updated, 0 files merged, 0 files removed, 0 files unresolved
$

Now the working copy should be updated to just-commited revision. To load the package back into freshly started Smalltalk/X IDE, load the package as usual:

Smalltalk loadPackage: 'jv:demos/helloworld_1'.

If there's no error while loading (there should not be), you may want to try whether it works as expected. Evaluate:

HelloWorldStartup main

You should see text "Hello world!" in Transcript window. You should be able to see jv.demos.helloworld_1.core.HelloWorld class in a system browser window. Now you can change classes further and once done with it, commit and load it back using the same process.