org.jcsp.awt
Class ActiveApplet

java.lang.Object
  java.awt.Component
      java.awt.Container
          java.awt.Panel
              java.applet.Applet
                  org.jcsp.awt.ActiveApplet

All Implemented Interfaces:

ImageObserver, MenuContainer, Serializable, Accessible, CSProcess

public class ActiveApplet
extends Applet
implements CSProcess

java.applet.Applet with a channel interface, specialising in the operation of CSProcess networks as applets.

Shortcut to the Constructor and Method Summaries.

Description

ActiveApplet is an extension of Applet to simplify the management of an associated CSProcess. There are three areas of provision:

• controlling the execution of the associated process;
• a channel interface to and from the underlying Panel;
• some methods to help accessing applet parameters.

These mechanisms are described in the next three sections.

Applet Processes

In an application, a network of processes can be executed simply by invoking run on the defining (Parallel) process from the main thread of control. We cannot do this from the applet init or start methods since the browser would freeze until the process network terminated. Instead, the process network must be started asynchronously with the applet thread. This can be achieved by using a ProcessManager.

We could do this by directly extending the Applet class and overriding its start, stop and destroy methods suitably - however, the necessary logic has already been built into this class. All the user needs to do is override the init method to contruct the desired CSProcess and register it with this ActiveApplet (by means of the setProcess method).

For example:

 import org.jcsp.awt.*;
 
 public class Flasher extends ActiveApplet {
 
   public void init () {
     setProcess (new FlasherNetwork (500, this));
   }
 
 }
 

In the above, FlasherNetwork is the CSProcess that will be run by the ActiveApplet. The 500 parameter defines the period (in milliseconds) of its flashing and should really be a parameter of the applet itself. The reason for passing the reference to this into the FlasherNetwork process is explained in the description of its implementation in the next section.

Default ActiveApplet stop/start/destroy Behaviour

The default behaviours of the start, stop and destroy methods implemented by this ActiveApplet are as follows.

When the HTML browser invokes start for the first time, the CSProcess (registered by the setProcess method) will be set running in its own thread of control. As the browser subsequently invokes stop and start methods, events will be posted to channels which may be optionally registered with the Applet.

When the browser invokes destroy, an event will be posted to the optionally registered channel. If this is not present or does not cause network termination the process network will be forcefully destroyed.

Sun's Java Plug-in

Most of the problems arising from the default ActiveApplet controls are avoided by taking note of the following:

Use of this ActiveApplet class is recommended only for browsers on systems that have installed Sun's Java Plug-in.

This has the robust behaviour of invoking a destroy immediately following a stop whenever we leave a web page containing a Plug-in controlled applet. It re-launches the applet from scratch whenever we return. Whilst this removes the option of allowing applets continued execution during visits to other pages (but see the cheat), it does relieve various deadlock problems that may otherwise strike our browser.

Note: to use the Java Plug-in, HTML pages containing applets must be transformed using the Java Plug-in HTML Converter. This renders the HTML somewhat more complex than it was before conversion, but the results are worthwhile. A browser visiting such a page without the Plug-in installed is invited to install it - a link is offered to make this easy.

User-Defined Applet stop/start/destroy Behaviours

The applet stop, start and destroy methods can, of course, be overridden by the user to interact in some user-chosen way with the process associated with the ActveApplet. However, the proper way to interact with a process is to communicate with it over a channel and support for this is provided without the user having to override anything.

The methods setStopStartChannel and setDestroyChannels let us connect special channels to the ActveApplet process:

If a stopStart channel has been set, an ActiveApplet.STOP (respectively ActiveApplet.START) will be written to this channel whenever the browser invokes a stop (respectively start) method. As before, the first invocation of start just starts the running of the associated process (i.e. ActiveApplet.START messages are only sent on second and subsequent starts). This replaces the default start and stop mechanisms described earlier.

If a pair of destroy/destroyAck channels have been set, an ActiveApplet.DESTROY will be written to the destroy channel when the browser invokes its destroy method. The browser will wait for up to 10 seconds (by default) for the applet process to respond with a message on destroyAck, before proceeding to execute the default destroy mechanisms. The timeout period can be specified (or disabled) when the channels are set.

These channels should be set up either as an explicit part of the init method (and passed to the user process as a constructor or mutator parameter) or by the user process constructor itself (to which this ActveApplet would have had to have been passed). It is important that these channels are in place before the user process starts running (otherwise the default mechanism may be triggered if the user quits the ActveApplet web page or the browser too quickly).

It is crucial, of course, that these communications are accepted by the user process associated with the ActveApplet. Using a channel configured with an overwriting buffer (of capacity one) will ensure this. Note that this overwriting cannot cause the loss of any significant information to the user process.

The stop/start and destroy operations are implemented via separately set channels so that the designer may make separate decisions on whether to use each of them.

Freezing a process network (e.g. in response to a STOP is usually easy to arrange - just pinch the data-flow at a crucial point to achieve a temporary deadlock. When the START message arrives, just let go.

Note: if the Java Plug-in is not being used, it is strongly recommended to set and operate this stopStart channel (rather than rely on the default suspend operations).

Note: if the Java Plug-in is being used, user-defined behaviour for the stop/start operations are not needed. Any stop is quickly followed by a destroy (for which the default ActveApplet response will release any locked resource). Second invocations of start never take place.

The destroy/destroyAck channels enable the process network to tidy up any created resources (e.g. to make invisible and dispose of any widgets spawned off the web page) before termination. Correctly terminating a process network (e.g. in response to a destroy) is usually harder to arrange safely - so it may be better to leave this to the default mechanism (which will follow the destroyAck signal). However, secure CSP algorithms, at least for 1-1 channels, are known (e.g. the graceful termination protocol) and support for this may be provided in later versions of this library.

Note: if the destroy/destroyAck channels have been set, the default suspend mechanism (if not already overridden by setting a stopStart channel) will be suppressed. This is because the browser invokes the stop method immediately before invoking the destroy. If we did not do this, the suspended network would not be able to respond to the destroy channel.

The ActveApplet as an ActivePanel

An ActveApplet extends a java.applet.Applet which extends a java.awt.Panel. Most activeApplets will just use this panel as a container for other active GUI processes that form part of their ActiveApplet network. However, if there is a need for run-time configuration of the underlying panel and/or reaction to GUI events occurring on the panel, the ActveApplet can itself be used as a process in that network. Fot this case, an ActveApplet has a channel interface (which, together with the browser control channels, extends that offered by an ActivePanel):

The event channels should be connected to one or more application-specific server processes (instead of registering a passive object as a Listener to this component).

All channels are optional. The configure channel is connected by invoking the setConfigureChannel method. Event channels can be added to notify the occurrence of any type of Event the component generates (by calling the appropriate addXXXEventChannel method before the process is run). Messages can be sent down the configure channel at any time to configure the component. See the table below for details.

All channels are managed by independent internal handler processes. It is, therefore, safe for a serial application process both to service an event channel and configure the component -- no deadlock can occur.

IMPORTANT: it is essential that event channels from this process are always serviced -- otherwise the Java Event Thread will be blocked and the GUI will stop responding. A simple way to guarantee this is to use channels configured with overwriting buffers. For example:

   final One2OneChannel myMouseEvent =
     Channel.one2one (new OverWriteOldestBuffer (n));
 
   activeApplet.addMouseEventChannel (myMouseEvent);
 

This will ensure that the Java Event Thread will never be blocked. Slow or inattentive readers may miss rapidly generated events, but the n most recent events will always be available.

Channel Protocols

Input Channels
destroyAck	int	See the setDestroyChannels methods.
configure	ActiveApplet.Configure	Invoke the user-defined Configure.configure method on the applet.
Output Channels
stopStart	int	See the setStopStartChannel method.
destroy	int	See the setDestroyChannels methods.
containerEvent	ContainerEvent	See the addContainerEventChannel method.
componentEvent	ComponentEvent	See the addComponentEventChannel method.
focusEvent	FocusEvent	See the addFocusEventChannel method.
keyEvent	KeyEvent	See the addKeyEventChannel method.
mouseEvent	MouseEvent	See the addMouseEventChannel method.
mouseMotionEvent	MouseEvent	See the addMouseMotionEventChannel method.

Example

This example continues the Flasher example introduced earlier. FlasherNetwork consists of two processes: one is the ActiveApplet (supplied as a parameter to its constructor) and the other is a user-written FlasherControl. Here is the network diagram:

FlasherControl responds to mouse entry and exit events on the applet area (delivered as messages down the mouseEvent channel). When the mouse is outside the applet, the applet is painted black. When the mouse is inside the applet, FlasherControl paints the applet a random colour every period milliseconds (where period is the other parameter to its constructor). The applet colour is controlled by sending it a message down the appletConfigure channel.

Here is the code to set up this process:

 import org.jcsp.lang.*;
 import org.jcsp.awt.*;
 
 public class FlasherNetwork implements CSProcess {
 
   final private long period;
   final private ActiveApplet activeApplet;
 
   public FlasherNetwork (final long period,
                          final ActiveApplet activeApplet) {
     this.period = period;
     this.activeApplet = activeApplet;
   }
 
   public void run () {
 
     final One2OneChannel mouseEvent = Channel.one2one ();
     final One2OneChannel appletConfigure = Channel.one2one ();
 
     activeApplet.addMouseEventChannel (mouseEvent.out ());
     activeApplet.setConfigureChannel (appletConfigure.in ());
 
     new Parallel (
       new CSProcess[] {
         activeApplet,
         new FlasherControl (period, mouseEvent.in (), appletConfigure.out ())
       }
     ).run ();
 
   }
 
 }
 

FlasherControl demonstrates three basic JCSP techniques:

• ALTing between guards (a channel communication and a timeout);
• ALTing with pre-conditions (the mouse must be present in the applet for the flashing - controlled by the timeout - to take place);
• construction and use of general configuration objects for an Active GUI process (including the double-buffering needed for security when reusing these objects - see the note in ActiveApplet.Configure).

For completeness, here is its definition:

 import org.jcsp.lang.*;
 import org.jcsp.awt.*;
 import java.awt.*;
 import java.awt.event.*;
 import java.util.*;
 
 public class FlasherControl implements CSProcess {
 
   final private long period;
   final private AltingChannelInput mouseEvent;
   final private ChannelOutput appletConfigure;
 
   public FlasherControl (final long period,
                          final AltingChannelInput mouseEvent,
                          final ChannelOutput appletConfigure) {
     this.period = period;
     this.mouseEvent = mouseEvent;
     this.appletConfigure = appletConfigure;
   }
 
   private class AppletColour implements ActiveApplet.Configure {
     private Color colour = Color.lightGray;
     public void setColour (Color colour) {
       this.colour = colour;
     }
     public void configure (java.applet.Applet applet) {
       applet.setBackground (colour);
     }
   }
 
   public void run () {
 
     final Random random = new Random ();
     final CSTimer tim = new CSTimer ();
 
     final Alternative alt = new Alternative (new Guard[] {mouseEvent, tim});
     final boolean[] preCondition = {true, false};
     final int MOUSE = 0;
     final int TIMER = 1;
 
     final AppletColour[] appletColour = {new AppletColour (), new AppletColour ()};
     final AppletColour panelBlack = new AppletColour ();
     panelBlack.setColour (Color.black);
 
     appletConfigure.write (panelBlack);
 
     int index = 0;
     AppletColour appletCol = appletColour[index];
     appletCol.setColour (new Color (random.nextInt ()));
 
     long timeout = tim.read ();
     boolean mousePresent = false;
     boolean running = true;
 
     while (running) {
 
       switch (alt.priSelect (preCondition)) {
 
         case MOUSE:
           switch (((MouseEvent) mouseEvent.read ()).getID ()) {
             case MouseEvent.MOUSE_ENTERED:
               if (! mousePresent) {
                 mousePresent = true;
                 timeout = tim.read () + period;
                 tim.setAlarm (timeout);
                 appletConfigure.write (appletCol);
                 preCondition[TIMER] = true;
               }
             break;
             case MouseEvent.MOUSE_EXITED:
               if (mousePresent) {
                 mousePresent = false;
                 appletConfigure.write (panelBlack);
                 preCondition[TIMER] = false;
               }
             break;
           }
         break;
 
         case TIMER:
           timeout += period;
           tim.setAlarm (timeout);
           index = 1 - index;
           appletCol = appletColour[index];
           appletCol.setColour (new Color (random.nextInt ()));
           appletConfigure.write (appletCol);
         break;
 
       }
 
     }
 
   }
 
 }
 

Accessing Applet Parameters

ActveApplet provides a set of methods for simplifying the acquisition of parameters from the HTML source code. These methods are not specific for JCSP - they are useful for any applets.

All methods getAppletXXX have the same form, where XXX is one of Java's primitive types (int, boolean, byte, short, long, float and double). Each returns an XXX value, parsed from the applet parameter named in the method's first parameter. A standby value must be supplied in case the named applet parameter does not exist or parse correctly. The number returning methods must supply min and max values against which the applet supplied value will be checked - values below min being truncated to min and values above max to max.

For example, Flasher should really acquire its period value as an applet parameter:

 import org.jcsp.lang.*;
 import org.jcsp.awt.*;
 import java.awt.*;
 
 public class Flasher extends ActiveApplet {
 
   public static final int minPeriod = 300;       // milliseconds
   public static final int maxPeriod = 1000;      // milliseconds
   public static final int defaultPeriod = 500;   // milliseconds
 
   public void init () {
 
     final int period =
       getAppletInt ("period", minPeriod, maxPeriod, defaultPeriod);
 
     setProcess (new FlasherNetwork (period, this));
 
   }
 
 }
 

Now, if no applet parameter "period" is present, the defaultPeriod is chosen. Same if the parameter was present but doesn't parse. Otherwise, values below minPeriod are rounded up to minPeriod, values above maxPeriod are rounded down to maxPeriod and good values are just accepted.

Author:

P.D. Austin and P.H. Welch

See Also:

Applet, Panel, ContainerEvent, ComponentEvent, FocusEvent, KeyEvent, MouseEvent, OverWriteOldestBuffer, Serialized Form

Nested Class Summary

static interface

ActiveApplet.Configure This enables general configuration of this component.

Nested classes/interfaces inherited from class java.applet.Applet

Applet.AccessibleApplet

Nested classes/interfaces inherited from class java.awt.Panel

Panel.AccessibleAWTPanel

Nested classes/interfaces inherited from class java.awt.Container

Container.AccessibleAWTContainer

Nested classes/interfaces inherited from class java.awt.Component

Component.AccessibleAWTComponent, Component.BltBufferStrategy, Component.FlipBufferStrategy

Field Summary

static int	DEFAULT_TIMEOUT_ACK This is the default time (in milliseconds) that the browser will wait for the applet process to acknowledge (on destroyAck) a DESTROY message (sent down destroy).
static int	DESTROY This value is sent down a destroy channel when the browser invokes a destroy - see the user-defined destroy response.
static int	START This value is sent down a stopStart channel on second and subsequent browser invocations of start - see the user-defined stop/start response.
static int	STOP This value is sent down a stopStart channel when the browser invokes a stop - see the user-defined stop/start response.

Fields inherited from class java.awt.Component

BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT

Fields inherited from interface java.awt.image.ImageObserver

ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH

Constructor Summary

ActiveApplet()

Method Summary

void	addComponentEventChannel(ChannelOutput componentEvent) Add a new channel to this component that will be used to notify that a ComponentEvent has occurred.
void	addContainerEventChannel(ChannelOutput containerEvent) Add a new channel to this component that will be used to notify that a ContainerEvent has occurred.
void	addFocusEventChannel(ChannelOutput focusEvent) Add a new channel to this component that will be used to notify that a FocusEvent has occurred.
void	addKeyEventChannel(ChannelOutput keyEvent) Add a new channel to this component that will be used to notify that a KeyEvent has occurred.
void	addMouseEventChannel(ChannelOutput mouseEvent) Add a new channel to this component that will be used to notify that a MouseEvent has occurred.
void	addMouseMotionEventChannel(ChannelOutput mouseMotionEvent) Add a new channel to this component that will be used to notify that a MouseMotionEvent has occurred.
void	destroy() Called by the browser when the ActiveApplet needs to be destroyed.
boolean	getAppletBoolean(String parameter, boolean standby) This looks for the named parameter in the HTML applet source code and attempts to parse it into a boolean.
byte	getAppletByte(String parameter, byte min, byte max, byte standby) This looks for the named parameter in the HTML applet source code and attempts to parse it into a byte.
double	getAppletDouble(String parameter, double min, double max, double standby) This looks for the named parameter in the HTML applet source code and attempts to parse it into a double.
float	getAppletFloat(String parameter, float min, float max, float standby) This looks for the named parameter in the HTML applet source code and attempts to parse it into a float.
int	getAppletInt(String parameter, int min, int max, int standby) This looks for the named parameter in the HTML applet source code and attempts to parse it into an int.
long	getAppletLong(String parameter, long min, long max, long standby) This looks for the named parameter in the HTML applet source code and attempts to parse it into a long.
short	getAppletShort(String parameter, short min, short max, short standby) This looks for the named parameter in the HTML applet source code and attempts to parse it into a short.
void	run() The main body of this process.
void	setConfigureChannel(ChannelInput configure) Sets the configuration channel for this ActiveApplet.
void	setDestroyChannels(ChannelOutputInt destroy, AltingChannelInputInt destroyAck) This sets destroy/destroyAck channels to allow a user-defined destroy response.
void	setDestroyChannels(ChannelOutputInt destroy, AltingChannelInputInt destroyAck, int timeoutAck) This sets destroy/destroyAck channels to allow a user-defined destroy response.
void	setProcess(CSProcess process) This must be called during the init() method for this ActiveApplet.
void	setStopStartChannel(ChannelOutputInt stopStart) This sets a stopStart channel to allow a user-defined stop/start response.
void	start() Called by the browser when the ActiveApplet is first started and each time its web page is revisited.
void	stop() Called by the browser when the web page containing this ActiveApplet is replaced by another page or just before this ActiveApplet is to be destroyed.

Methods inherited from class java.applet.Applet

getAccessibleContext, getAppletContext, getAppletInfo, getAudioClip, getAudioClip, getCodeBase, getDocumentBase, getImage, getImage, getLocale, getParameter, getParameterInfo, init, isActive, newAudioClip, play, play, resize, resize, setStub, showStatus

Methods inherited from class java.awt.Panel

addNotify

Methods inherited from class java.awt.Container

add, add, add, add, add, addContainerListener, addImpl, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, countComponents, deliverEvent, doLayout, findComponentAt, findComponentAt, getAlignmentX, getAlignmentY, getComponent, getComponentAt, getComponentAt, getComponentCount, getComponents, getComponentZOrder, getContainerListeners, getFocusTraversalKeys, getFocusTraversalPolicy, getInsets, getLayout, getListeners, getMaximumSize, getMinimumSize, getMousePosition, getPreferredSize, insets, invalidate, isAncestorOf, isFocusCycleRoot, isFocusCycleRoot, isFocusTraversalPolicyProvider, isFocusTraversalPolicySet, layout, list, list, locate, minimumSize, paint, paintComponents, paramString, preferredSize, print, printComponents, processContainerEvent, processEvent, remove, remove, removeAll, removeContainerListener, removeNotify, setComponentZOrder, setFocusCycleRoot, setFocusTraversalKeys, setFocusTraversalPolicy, setFocusTraversalPolicyProvider, setFont, setLayout, transferFocusBackward, transferFocusDownCycle, update, validate, validateTree

Methods inherited from class java.awt.Component

action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addMouseWheelListener, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, createVolatileImage, createVolatileImage, disable, disableEvents, dispatchEvent, enable, enable, enableEvents, enableInputMethods, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, getBackground, getBounds, getBounds, getColorModel, getComponentListeners, getComponentOrientation, getCursor, getDropTarget, getFocusCycleRootAncestor, getFocusListeners, getFocusTraversalKeysEnabled, getFont, getFontMetrics, getForeground, getGraphics, getGraphicsConfiguration, getHeight, getHierarchyBoundsListeners, getHierarchyListeners, getIgnoreRepaint, getInputContext, getInputMethodListeners, getInputMethodRequests, getKeyListeners, getLocation, getLocation, getLocationOnScreen, getMouseListeners, getMouseMotionListeners, getMousePosition, getMouseWheelListeners, getName, getParent, getPeer, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getSize, getToolkit, getTreeLock, getWidth, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, isBackgroundSet, isCursorSet, isDisplayable, isDoubleBuffered, isEnabled, isFocusable, isFocusOwner, isFocusTraversable, isFontSet, isForegroundSet, isLightweight, isMaximumSizeSet, isMinimumSizeSet, isOpaque, isPreferredSizeSet, isShowing, isValid, isVisible, keyDown, keyUp, list, list, list, location, lostFocus, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, postEvent, prepareImage, prepareImage, printAll, processComponentEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, processMouseWheelEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeMouseWheelListener, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, reshape, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFocusable, setFocusTraversalKeysEnabled, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusUpCycle

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

STOP

public static final int STOP

This value is sent down a stopStart channel when the browser invokes a stop - see the user-defined stop/start response.

See Also:

Constant Field Values

START

public static final int START

This value is sent down a stopStart channel on second and subsequent browser invocations of start - see the user-defined stop/start response.

See Also:

Constant Field Values

DESTROY

public static final int DESTROY

This value is sent down a destroy channel when the browser invokes a destroy - see the user-defined destroy response.

See Also:

Constant Field Values

DEFAULT_TIMEOUT_ACK

public static final int DEFAULT_TIMEOUT_ACK

This is the default time (in milliseconds) that the browser will wait for the applet process to acknowledge (on destroyAck) a DESTROY message (sent down destroy). The default value is 10000 (i.e. 10 seconds). See the user-defined destroy response.

See Also:

Constant Field Values

Constructor Detail

ActiveApplet

public ActiveApplet()

Method Detail

setProcess

public void setProcess(CSProcess process)

This must be called during the init() method for this ActiveApplet. It defines the process that is to be managed.

Parameters:

process - the process defining the applet behaviour.

setStopStartChannel

public void setStopStartChannel(ChannelOutputInt stopStart)

This sets a stopStart channel to allow a user-defined stop/start response. If the channel passed is null, no action will be taken.

Parameters:

stopStart - the channel controlling the stop/start behaviour of the applet.

setDestroyChannels

public void setDestroyChannels(ChannelOutputInt destroy,
                               AltingChannelInputInt destroyAck)

This sets destroy/destroyAck channels to allow a user-defined destroy response. If either channel passed is null, no action will be taken. A default timeout delay (10000 milliseconds) for the applet process to acknowledge the destroy signal is set.

Parameters:

destroy - the channel to which a DESTROY will be written.

destroyAck - the acknowledgement channel associated with destroy.

setDestroyChannels

public void setDestroyChannels(ChannelOutputInt destroy,
                               AltingChannelInputInt destroyAck,
                               int timeoutAck)

This sets destroy/destroyAck channels to allow a user-defined destroy response. If either channel passed is null, no action will be taken. The timeout delay for the applet process to acknowledge the destroy signal is set by timeoutAck. If this is set negative, no timeout will be set - i.e. the browser will wait indefinitely (which may cause a problem if the applet process is mis-programmed).

Parameters:

destroy - the channel to which a DESTROY will be written.

destroyAck - the acknowledgement channel associated with destroy.

timeoutAck - the timeout (in milliseconds) allowed for the acknowledgement - if negative, no timeout will be set.

start

public void start()

Called by the browser when the ActiveApplet is first started and each time its web page is revisited. See above for the default and user-definable behaviours obtainable from this method.

Overrides:

start in class Applet

stop

public void stop()

Called by the browser when the web page containing this ActiveApplet is replaced by another page or just before this ActiveApplet is to be destroyed. See above for the default and user-definable behaviours obtainable from this method.

Overrides:

stop in class Applet

destroy

public void destroy()

Called by the browser when the ActiveApplet needs to be destroyed. See above for the default and user-definable behaviours obtainable from this method.

Overrides:

destroy in class Applet

getAppletInt

public int getAppletInt(String parameter,
                        int min,
                        int max,
                        int standby)

This looks for the named parameter in the HTML applet source code and attempts to parse it into an int. If all is well, the value is checked that it lies between min and max inclusive and then returned. If the parameter is not present or doesn't parse, the standby value is returned. If the checks fail, the value is truncated to either min or max (depending on the direction of the error) and returned.

Parameters:

parameter - the applet parameter name.

min - the minimum acceptable parameter value.

max - the maximum acceptable parameter value.

standby - the value to retun in case the applet parameter is bad.

Returns:

either the value of the named parameter or standby.

getAppletBoolean

public boolean getAppletBoolean(String parameter,
                                boolean standby)

This looks for the named parameter in the HTML applet source code and attempts to parse it into a boolean. If the parameter is not present or doesn't parse, the standby value is returned.

Parameters:

parameter - the applet parameter name.

standby - the value to retun in case the applet parameter is bad.

Returns:

either the value of the named parameter or standby.

getAppletByte

public byte getAppletByte(String parameter,
                          byte min,
                          byte max,
                          byte standby)

This looks for the named parameter in the HTML applet source code and attempts to parse it into a byte. If all is well, the value is checked that it lies between min and max inclusive and then returned. If the parameter is not present or doesn't parse, the standby value is returned. If the checks fail, the value is truncated to either min or max (depending on the direction of the error) and returned.

Parameters:

parameter - the applet parameter name.

min - the minimum acceptable parameter value.

max - the maximum acceptable parameter value.

standby - the value to retun in case the applet parameter is bad.

Returns:

either the value of the named parameter or standby.

getAppletShort

public short getAppletShort(String parameter,
                            short min,
                            short max,
                            short standby)

This looks for the named parameter in the HTML applet source code and attempts to parse it into a short. If all is well, the value is checked that it lies between min and max inclusive and then returned. If the parameter is not present or doesn't parse, the standby value is returned. If the checks fail, the value is truncated to either min or max (depending on the direction of the error) and returned.

Parameters:

parameter - the applet parameter name.

min - the minimum acceptable parameter value.

max - the maximum acceptable parameter value.

standby - the value to retun in case the applet parameter is bad.

Returns:

either the value of the named parameter or standby.

getAppletLong

public long getAppletLong(String parameter,
                          long min,
                          long max,
                          long standby)

This looks for the named parameter in the HTML applet source code and attempts to parse it into a long. If all is well, the value is checked that it lies between min and max inclusive and then returned. If the parameter is not present or doesn't parse, the standby value is returned. If the checks fail, the value is truncated to either min or max (depending on the direction of the error) and returned.

Parameters:

parameter - the applet parameter name.

min - the minimum acceptable parameter value.

max - the maximum acceptable parameter value.

standby - the value to retun in case the applet parameter is bad.

Returns:

either the value of the named parameter or standby.

getAppletFloat

public float getAppletFloat(String parameter,
                            float min,
                            float max,
                            float standby)

This looks for the named parameter in the HTML applet source code and attempts to parse it into a float. If all is well, the value is checked that it lies between min and max inclusive and then returned. If the parameter is not present or doesn't parse, the standby value is returned. If the checks fail, the value is truncated to either min or max (depending on the direction of the error) and returned.

Parameters:

parameter - the applet parameter name.

min - the minimum acceptable parameter value.

max - the maximum acceptable parameter value.

standby - the value to retun in case the applet parameter is bad.

Returns:

either the value of the named parameter or standby.

getAppletDouble

public double getAppletDouble(String parameter,
                              double min,
                              double max,
                              double standby)

This looks for the named parameter in the HTML applet source code and attempts to parse it into a double. If all is well, the value is checked that it lies between min and max inclusive and then returned. If the parameter is not present or doesn't parse, the standby value is returned. If the checks fail, the value is truncated to either min or max (depending on the direction of the error) and returned.

Parameters:

parameter - the applet parameter name.

min - the minimum acceptable parameter value.

max - the maximum acceptable parameter value.

standby - the value to retun in case the applet parameter is bad.

Returns:

either the value of the named parameter or standby.

setConfigureChannel

public void setConfigureChannel(ChannelInput configure)

Sets the configuration channel for this ActiveApplet.

Parameters:

configure - the channel for configuration events. If the channel passed is null, no action will be taken.

addContainerEventChannel

public void addContainerEventChannel(ChannelOutput containerEvent)

Add a new channel to this component that will be used to notify that a ContainerEvent has occurred. This should be used instead of registering a ContainerListener with the component. It is possible to add more than one Channel by calling this method multiple times. If the channel passed is null, no action will be taken.

NOTE: This method must be called before this process is run.

Parameters:

containerEvent - the channel down which to send ContainerEvents.

addComponentEventChannel

public void addComponentEventChannel(ChannelOutput componentEvent)

Add a new channel to this component that will be used to notify that a ComponentEvent has occurred. This should be used instead of registering a ComponentListener with the component. It is possible to add more than one Channel by calling this method multiple times. If the channel passed is null, no action will be taken.

NOTE: This method must be called before this process is run.

Parameters:

componentEvent - the channel down which to send ComponentEvents.

addFocusEventChannel

public void addFocusEventChannel(ChannelOutput focusEvent)

Add a new channel to this component that will be used to notify that a FocusEvent has occurred. This should be used instead of registering a FocusListener with the component. It is possible to add more than one Channel by calling this method multiple times. If the channel passed is null, no action will be taken.

NOTE: This method must be called before this process is run.

Parameters:

focusEvent - the channel down which to send FocusEvents.

addKeyEventChannel

public void addKeyEventChannel(ChannelOutput keyEvent)

Add a new channel to this component that will be used to notify that a KeyEvent has occurred. This should be used instead of registering a KeyListener with the component. It is possible to add more than one Channel by calling this method multiple times. If the channel passed is null, no action will be taken.

NOTE: This method must be called before this process is run.

Parameters:

keyEvent - the channel down which to send KeyEvents.

addMouseEventChannel

public void addMouseEventChannel(ChannelOutput mouseEvent)

Add a new channel to this component that will be used to notify that a MouseEvent has occurred. This should be used instead of registering a MouseListener with the component. It is possible to add more than one Channel by calling this method multiple times. If the channel passed is null, no action will be taken.

NOTE: This method must be called before this process is run.

Parameters:

mouseEvent - the channel down which to send MouseEvents.

addMouseMotionEventChannel

public void addMouseMotionEventChannel(ChannelOutput mouseMotionEvent)

Add a new channel to this component that will be used to notify that a MouseMotionEvent has occurred. This should be used instead of registering a MouseMotionListener with the component. It is possible to add more than one Channel by calling this method multiple times. If the channel passed is null, no action will be taken.

NOTE: This method must be called before this process is run.

Parameters:

mouseMotionEvent - the channel down which to send MouseMotionEvents.

run

public void run()

The main body of this process.

Specified by:

run in interface CSProcess