src/java.desktop/share/classes/javax/imageio/metadata/IIOMetadataController.java

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package javax.imageio.metadata;

/**
 * An interface to be implemented by objects that can determine the
 * settings of an {@code IIOMetadata} object, either by putting
 * up a GUI to obtain values from a user, or by other means.  This
 * interface merely specifies a generic {@code activate} method
 * that invokes the controller, without regard for how the controller
 * obtains values (<i>i.e.</i>, whether the controller puts up a GUI
 * or merely computes a set of values is irrelevant to this
 * interface).
 *
 * <p> Within the {@code activate} method, a controller obtains
 * initial values by querying the {@code IIOMetadata} object's
 * settings, either using the XML DOM tree or a plug-in specific
 * interface, modifies values by whatever means, then modifies the
 * {@code IIOMetadata} object's settings, using either the
 * {@code setFromTree} or {@code mergeTree} methods, or a
 * plug-in specific interface.  In general, applications may expect
 * that when the {@code activate} method returns
 * {@code true}, the {@code IIOMetadata} object is ready for
 * use in a write operation.
 *
 * <p> Vendors may choose to provide GUIs for the
 * {@code IIOMetadata} subclasses they define for a particular
 * plug-in.  These can be set up as default controllers in the
 * corresponding {@code IIOMetadata} subclasses.
 *
 * <p> Alternatively, an algorithmic process such as a database lookup
 * or the parsing of a command line could be used as a controller, in
 * which case the {@code activate} method would simply look up or
 * compute the settings, call methods on {@code IIOMetadata} to
 * set its state, and return {@code true}.
 *
 * @see IIOMetadata#setController
 * @see IIOMetadata#getController
 * @see IIOMetadata#getDefaultController
 * @see IIOMetadata#hasController
 * @see IIOMetadata#activateController
 *
 */
public interface IIOMetadataController {

    /**
     * Activates the controller.  If {@code true} is returned,
     * all settings in the {@code IIOMetadata} object should be
     * ready for use in a write operation.  If {@code false} is
     * returned, no settings in the {@code IIOMetadata} object
     * will be disturbed (<i>i.e.</i>, the user canceled the
     * operation).
     *
     * @param metadata the {@code IIOMetadata} object to be modified.
     *
     * @return {@code true} if the {@code IIOMetadata} has been
     * modified, {@code false} otherwise.
     *
     * @throws IllegalArgumentException if {@code metadata} is
     * {@code null} or is not an instance of the correct class.
     */
    boolean activate(IIOMetadata metadata);
}