HolonJ

 HolonJForth

 UsingHolonJ
    Testing/Console
    Testing/Jmon
    Debugging
    Apps&Applets
    Access
    Style

You can create Java applications and applets in HolonJ. Here are some observations.

Minimal Application

An application is a class with a main method.

class: Hello

: main   ( String [] args -- )
    ." hello world"   ;

Application with a window

If an object of the class is created, the method <init> is called for initializing. At the very least <init> initializes the super object. 

class: MyApp extends Frame

i: MyApp.<init>   ( -- )
     " My window"  initsuper ()  ;

: main   ( String [] args -- )
     MyApp m  new m ()
     300 300 m setSize
     m showWindow   ;

If an identifier contains a dot, only the part of the identifier following the dot is used in the class file. Thus HolonJ sees "MyApp.<init>", Java sees "<init>".

Minimal Applet

An applet is a class that extends the class Applet and runs in a browser. The browser loads the applet, creates an object and calls the init method of the applet.

class: MyApplet extends Applet

i: MyApplet.<init>   ( -- )
    initsuper ()  ;

i: MyApplet.init   ( -- )    ;

Useful Applet

Running as a thread, no user input

class: MyApplet  extends Applet   implements Runnable

Thread Clock

i: MyApplet.start   ( -- )    
      this new Thread ( runnable -- ) is Clock
      Clock startThread ;

i: MyApplet.paint ( Graphics g -- ) 
    TimeString 40 100 g drawString ;

i: MyApplet.run   ( -- )  
     begin this repaint 1000. sleep again  ;

i: MyApplet.stop   ( -- )    
      Clock stopThread ;

Games, User action

class: MyApplet  extends Applet  implements MouseListerner

\ callback function
i: paint   ( Graphics g -- )   ;

i: mouseReleased ( mouseEvent e -- )   ;

i: mousePressed ( mouseEvent e -- )   ;

i: mouseClicked ( mouseEvent e -- )   ;

i: mouseEntered ( mouseEvent e -- )  ;

i: mouseExited ( mouseEvent e -- )   ;

Running the Applet as an Application

The applet can run as an application, if we provide a context with a window. The java interpreter does not provide a full applet context (e.g. no sound), but it serves well for the initial tests.

i: InFrame   ( -- )
    Frame f  " Testing my applet in a frame" new f ( string -- )
    this f addComponent drop 
    this this addMouselistener 
    300 300 f setSize  f showWindow   ;

: main ( string [] args -- )
     MyApplet m new m ()
     m InFrame ;

The window close button is not active. Close the window with Ctrl+C in the console window. Or add a window adapter class as in Calculator.