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Copyright © 2006 Sun Microsystems, Inc. All rights reserved.

javax.microedition.midlet
Class MIDlet

java.lang.Object
  |
  +--javax.microedition.midlet.MIDlet

public abstract class MIDlet

extends Object

A MIDLet is a MID Profile application. The application must extend this class to allow the application management software to control the MIDlet and to be able to retrieve properties from the application descriptor and notify and request state changes. The methods of this class allow the application management software to create, start, pause, and destroy a MIDlet. A MIDlet is a set of classes designed to be run and controlled by the application management software via this interface. The states allow the application management software to manage the activities of multiple MIDlets within a runtime environment. It can select which MIDlets are active at a given time by starting and pausing them individually. The application management software maintains the state of the MIDlet and invokes methods on the MIDlet to change states. The MIDlet implements these methods to update its internal activities and resource usage as directed by the application management software. The MIDlet can initiate some state changes itself and notifies the application management software of those state changes by invoking the appropriate methods.

Note: The methods on this interface signal state changes. The state change is not considered complete until the state change method has returned. It is intended that these methods return quickly.

Constructor Summary

protected

MIDlet() Protected constructor for subclasses.

Method Summary

protected abstract void	destroyApp(boolean unconditional) Signals the MIDlet to terminate and enter the Destroyed state.
String	getAppProperty(String key) Provides a MIDlet with a mechanism to retrieve named properties from the application management software.
void	notifyDestroyed() Used by an MIDlet to notify the application management software that it has entered into the Destroyed state.
void	notifyPaused() Notifies the application management software that the MIDlet does not want to be active and has entered the Paused state.
protected abstract void	pauseApp() Signals the MIDlet to stop and enter the Paused state.
void	resumeRequest() Provides a MIDlet with a mechanism to indicate that it is interested in entering the Active state.
protected abstract void	startApp() Signals the MIDlet that it has entered the Active state.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MIDlet

protected MIDlet()

Protected constructor for subclasses.

Method Detail

startApp

protected abstract void startApp()
                          throws MIDletStateChangeException

Signals the MIDlet that it has entered the Active state. In the Active state the MIDlet may hold resources. The method will only be called when the MIDlet is in the Paused state.

Two kinds of failures can prevent the service from starting, transient and non-transient. For transient failures the MIDletStateChangeException exception should be thrown. For non-transient failures the notifyDestroyed method should be called.

If a Runtime exception occurs during startApp the MIDlet will be destroyed immediately. Its destroyApp will be called allowing the MIDlet to cleanup.

Throws:

MIDletStateChangeException - is thrown if the MIDlet cannot start now but might be able to start at a later time.

pauseApp

protected abstract void pauseApp()

Signals the MIDlet to stop and enter the Paused state. In the Paused state the MIDlet must release shared resources and become quiescent. This method will only be called called when the MIDlet is in the Active state.

If a Runtime exception occurs during pauseApp the MIDlet will be destroyed immediately. Its destroyApp will be called allowing the MIDlet to cleanup.

destroyApp

protected abstract void destroyApp(boolean unconditional)
                            throws MIDletStateChangeException

Signals the MIDlet to terminate and enter the Destroyed state. In the destroyed state the MIDlet must release all resources and save any persistent state. This method may be called from the Paused or Active states.

MIDlets should perform any operations required before being terminated, such as releasing resources or saving preferences or state.

NOTE: The MIDlet can request that it not enter the Destroyed state by throwing an MIDletStateChangeException. This is only a valid response if the unconditional flag is set to false. If it is true the MIDlet is assumed to be in the Destroyed state regardless of how this method terminates. If it is not an unconditional request, the MIDlet can signify that it wishes to stay in its current state by throwing the MIDletStateChangeException. This request may be honored and the destroy() method called again at a later time.

If a Runtime exception occurs during destroyApp then they are ignored and the MIDlet is put into the Destroyed state.

Parameters:

unconditional - If true when this method is called, the MIDlet must cleanup and release all resources. If false the MIDlet may throw MIDletStateChangeException to indicate it does not want to be destroyed at this time.

Throws:

MIDletStateChangeException - is thrown if the MIDlet wishes to continue to execute (Not enter the Destroyed state). This exception is ignored if unconditional is equal to true.

notifyDestroyed

public final void notifyDestroyed()

Used by an MIDlet to notify the application management software that it has entered into the Destroyed state. The application management software will not call the MIDlet's destroyApp method, and all resources held by the MIDlet will be considered eligible for reclamation. The MIDlet must have performed the same operations (clean up, releasing of resources etc.) it would have if the MIDlet.destroyApp() had been called.

notifyPaused

public final void notifyPaused()

Notifies the application management software that the MIDlet does not want to be active and has entered the Paused state. Invoking this method will have no effect if the MIDlet is destroyed, or if it has not yet been started.

It may be invoked by the MIDlet when it is in the Active state.

If a MIDlet calls notifyPaused(), in the future its startApp() method may be called make it active again, or its destroyApp() method may be called to request it to destroy itself.

getAppProperty

public final String getAppProperty(String key)

Provides a MIDlet with a mechanism to retrieve named properties from the application management software. The properties are retrieved from the combination of the application descriptor file and the manifest. If an attributes in the descriptor has the same name as an attribute in the manifest the value from the descriptor is used and the value from the manifest is ignored.

Parameters:

key - the name of the property

Returns:

A string with the value of the property. null is returned if no value is available for the key.

Throws:

NullPointerException - is thrown if key is null.

resumeRequest

public final void resumeRequest()

Provides a MIDlet with a mechanism to indicate that it is interested in entering the Active state. Calls to this method can be used by the application management software to determine which applications to move to the Active state.

When the application management software decides to activate this application it will call the startApp method.

The application is generally in the Paused state when this is called. Even in the paused state the application may handle asynchronous events such as timers or callbacks.