Cache featuresOfTargets lists in GraphFeatureUpdateListeners.

This is called potentially very often, so it can become costly.

src/main/java/org/mastodon/feature/update/GraphFeatureUpdateListeners.java

@@ -1,10 +1,11 @@
 package org.mastodon.feature.update;
 
+import java.util.ArrayList;
 import java.util.List;
-import java.util.stream.Collectors;
 
 import org.mastodon.feature.Feature;
 import org.mastodon.feature.FeatureModel;
+import org.mastodon.feature.FeatureModel.FeatureModelListener;
 import org.mastodon.graph.Edge;
 import org.mastodon.graph.Vertex;
 import org.mastodon.properties.PropertyChangeListener;
@@ -27,7 +28,7 @@ public static < V extends Vertex< E >, E extends Edge< V > > PropertyChangeListe
 		return new MyVertexPropertyChangeListener<>( featureModel, vertexClass, edgeClass );
 	}
 
-	private static final class MyVertexPropertyChangeListener< V extends Vertex< E >, E extends Edge< V > > implements PropertyChangeListener< V >
+	private static final class MyVertexPropertyChangeListener< V extends Vertex< E >, E extends Edge< V > > implements PropertyChangeListener< V >, FeatureModelListener
 	{
 
 		private final FeatureModel featureModel;
@@ -36,33 +37,47 @@ private static final class MyVertexPropertyChangeListener< V extends Vertex< E >
 
 		private final Class< E > edgeClass;
 
+		private final List< Feature< E > > edgeFeatures;
+
+		private final List< Feature< V > > vertexFeatures;
+
 		public MyVertexPropertyChangeListener( final FeatureModel featureModel, final Class< V > vertexClass, final Class< E > edgeClass )
 		{
 			this.featureModel = featureModel;
 			this.vertexClass = vertexClass;
 			this.edgeClass = edgeClass;
+			this.edgeFeatures = new ArrayList<>();
+			this.vertexFeatures = new ArrayList<>();
+			featureModelChanged();
+			featureModel.listeners().add( this );
 		}
 
 		@Override
 		public void propertyChanged( final V v )
 		{
-			featuresOfTarget( featureModel, vertexClass ).forEach( f -> f.invalidate( v ) );
-			for ( final Feature< E > f : featuresOfTarget( featureModel, edgeClass ) )
+			vertexFeatures.forEach( f -> f.invalidate( v ) );
+			for ( final Feature< E > f : edgeFeatures )
 				v.edges().forEach( e -> f.invalidate( e ) );
 		}
-	}
 
-	// TODO: Revise! This is called potentially very often, so it can become costly.
-	//   Instead, MyVertexPropertyChangeListener should cache featuresOfTargets lists.
-	//   It should register a FeatureModelListener with the FeatureModel and update
-	//   the cached featuresOfTarget lists (only) when notified of changes.
-	private static < O > List< Feature< O > > featuresOfTarget( final FeatureModel featureModel, final Class< O > targetClass )
-	{
-		final List< ? > f = featureModel.getFeatureSpecs().stream()
-				.filter( fs -> fs.getTargetClass().equals( targetClass ) )
-				.map( fs -> featureModel.getFeature( fs ) ).collect( Collectors.toList() );
+		@Override
+		public void featureModelChanged()
+		{
+			featuresOfTarget( featureModel, vertexClass, vertexFeatures );
+			featuresOfTarget( featureModel, edgeClass, edgeFeatures );
+		}
+
 		@SuppressWarnings( "unchecked" )
-		final List< Feature< O > > typed = ( List< Feature< O > > ) f;
-		return typed;
+		private static < O > void featuresOfTarget(
+				final FeatureModel featureModel,
+				final Class< O > targetClass,
+				final List< Feature< O > > featureList )
+		{
+			featureList.clear();
+			featureModel.getFeatureSpecs()
+					.stream()
+					.filter( fs -> fs.getTargetClass().equals( targetClass ) )
+					.map( fs -> featureList.add( ( Feature< O > ) fs ) );
+		}
 	}
 }