// $Id: ArgoSingletonModule.java,v 1.5 2004/08/08 08:24:39 mvw Exp $
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package org.argouml.application.api;

/**  An interface which identifies an ArgoUML plug-in which behaves
 *   as a singleton, but may be swapped with another plugin singleton
 *   of the same type.  Only one singleton module can be considered
 *   active at the same time.
 *   
 *   @author Will Howery
 *   @author Thierry Lach
 *   @since  0.9.4
 */
public interface ArgoSingletonModule extends ArgoModule {

    /** Allows verification that the current singleton can be
     *  activated.  This is useful for determining menu entry
     *  availability, among other things.
     *  @return true if the singleton can be activated
     *          false otherwise.
     */
    public boolean canActivateSingleton();

    /** Allows verification that the current singleton can be
     *  deactivated.  This is useful for determining menu entry
     *  availability, among other things.
     *  @return true if the singleton can be deactivated
                false otherwise.
     */
    public boolean canDeactivateSingleton();

    /** Callback by which the active singleton is notified that it
     *  is being deactivated.  This is called prior to calling
     *  activateSingleton() on the new singleton.
     *
     *  After the call to deactivateSingleton() and
     *  before the call to activateSingleton(), the previously
     *  active singleton is considered to be the active singleton
     *  even though it is not marked as active.
     */
    public void deactivateSingleton();

    /** Callback by which the singleton being activated is notified that it
     *  is being activated.  This is called after calling
     *  deactivateSingleton() on the previous singleton.
     */
    public void activateSingleton();

    /**
     * TODO: Document this.
     * @return class which identifies the singleton
     */
    public Class getSingletonType();

} /* end interface ArgoSingletonModule */