import java.util.Collection;
import java.util.EventListener;
-import javax.annotation.Nonnull;
+import org.eclipse.jdt.annotation.NonNull;
import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidate;
/**
- * Interface implemented by classes interested in receiving notifications about
- * data tree changes. It provides a cursor-based view of the change.
+ * Interface implemented by classes interested in receiving notifications about data tree changes. It provides
+ * a cursor-based view of the change.
*/
public interface DOMDataTreeChangeListener extends EventListener {
/**
- * Invoked when there was data change for the supplied path, which was used
- * to register this listener.
+ * Invoked when there was data change for the supplied path, which was used to register this listener.
*
* <p>
- * This method may be also invoked during registration of the listener if
- * there is any pre-existing data in the conceptual data tree for supplied
- * path. This initial event will contain all pre-existing data as created.
+ * This method may be also invoked during registration of the listener if there is any pre-existing data
+ * in the conceptual data tree for supplied path. This initial event will contain all pre-existing data as created.
*
* <p>
- * A data change event may be triggered spuriously, e.g. such that data before
- * and after compare as equal. Implementations of this interface are expected
- * to recover from such events. Event producers are expected to exert reasonable
- * effort to suppress such events.
- * In other words, it is completely acceptable to observe
- * a {@link org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidateNode},
- * which reports a {@link org.opendaylight.yangtools.yang.data.api.schema.tree.ModificationType}
- * other than UNMODIFIED, while the before- and after- data items compare as
- * equal.
+ * Note: If there is no pre-existing data, the method {@link #onInitialData} will be invoked.
+ *
+ * <p>
+ * A data change event may be triggered spuriously, e.g. such that data before and after compare as equal.
+ * Implementations of this interface are expected to recover from such events. Event producers are expected to exert
+ * reasonable effort to suppress such events. In other words, it is completely acceptable to observe
+ * a {@link org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidateNode}, which reports
+ * a {@link org.opendaylight.yangtools.yang.data.api.schema.tree.ModificationType} other than UNMODIFIED, while
+ * the before- and after- data items compare as equal.
*
* @param changes Collection of change events, may not be null or empty.
+ * @throws NullPointerException if {@code changes} is null
+ */
+ void onDataTreeChanged(@NonNull Collection<DataTreeCandidate> changes);
+
+ /**
+ * Invoked only once during registration of the listener if there was no data in the conceptual data tree
+ * for the supplied path, which was used to register this listener, and after this
+ * {@link #onDataTreeChanged(Collection)} would always be invoked for data changes.
+ *
+ * <p>
+ * Default implementation does nothing and is appropriate for users who do not care about ascertaining
+ * initial stat.
*/
- void onDataTreeChanged(@Nonnull Collection<DataTreeCandidate> changes);
+ default void onInitialData() {
+ //no-op
+ }
}