Reduce memory overhead caused by default collection sizes

There are various collections that are usually not used at all or with
only a small number of items. Allocating the default sizes for such
collections wastes quite some memory: HashSet and HashMap allocate for
16 items by default, ArrayList for 10 items and IdentityHashMap for 32.

Reduces BasicElementView memory use from 429706 to 419682 bytes and the
memory use in BeverageBuddy with an edit dialog open from 290239 to
244149 bytes.

flow-data/src/main/java/com/vaadin/flow/data/binder/Binder.java

@@ -38,7 +38,6 @@
 import java.util.stream.Stream;
 
 import com.googlecode.gentyref.GenericTypeReflector;
-
 import com.vaadin.external.org.slf4j.Logger;
 import com.vaadin.external.org.slf4j.LoggerFactory;
 import com.vaadin.flow.component.Component;
@@ -786,7 +785,9 @@ public Binding<BEAN, TARGET> bind(ValueProvider<BEAN, TARGET> getter,
             getBinder().fireStatusChangeEvent(false);
 
             bound = true;
-            getBinder().incompleteBindings.remove(getField());
+            if (getBinder().incompleteBindings != null) {
+                getBinder().incompleteBindings.remove(getField());
+            }
 
             return binding;
         }
@@ -823,7 +824,10 @@ public Binding<BEAN, TARGET> bind(String propertyName) {
                 getBinder().boundProperties.put(propertyName, binding);
                 return binding;
             } finally {
-                getBinder().incompleteMemberFieldBindings.remove(getField());
+                if (getBinder().incompleteMemberFieldBindings != null) {
+                    getBinder().incompleteMemberFieldBindings
+                            .remove(getField());
+                }
             }
         }
 
@@ -1302,17 +1306,18 @@ void setIdentity() {
      */
     private final Map<String, Binding<BEAN, ?>> boundProperties = new HashMap<>();
 
-    private final Map<HasValue<?, ?>, BindingBuilder<BEAN, ?>> incompleteMemberFieldBindings = new IdentityHashMap<>();
+    private Map<HasValue<?, ?>, BindingBuilder<BEAN, ?>> incompleteMemberFieldBindings;
 
     private BEAN bean;
 
     private final Collection<Binding<BEAN, ?>> bindings = new ArrayList<>();
 
-    private final Map<HasValue<?, ?>, BindingBuilder<BEAN, ?>> incompleteBindings = new IdentityHashMap<>();
+    private Map<HasValue<?, ?>, BindingBuilder<BEAN, ?>> incompleteBindings;
 
     private final List<Validator<? super BEAN>> validators = new ArrayList<>();
 
-    private final Map<HasValue<?, ?>, ConverterDelegate<?>> initialConverters = new IdentityHashMap<>();
+    private final Map<HasValue<?, ?>, ConverterDelegate<?>> initialConverters = new IdentityHashMap<>(
+            4);
 
     private HashMap<Class<?>, List<SerializableConsumer<?>>> listeners = new HashMap<>();
 
@@ -1496,6 +1501,9 @@ public <FIELDVALUE> BindingBuilder<BEAN, FIELDVALUE> forField(
      */
     public <FIELDVALUE> BindingBuilder<BEAN, FIELDVALUE> forMemberField(
             HasValue<?, FIELDVALUE> field) {
+        if (incompleteMemberFieldBindings == null) {
+            incompleteMemberFieldBindings = new IdentityHashMap<>(8);
+        }
         incompleteMemberFieldBindings.put(field, null);
         return forField(field);
     }
@@ -2177,8 +2185,8 @@ public Registration addStatusChangeListener(StatusChangeListener listener) {
      */
     protected <T> Registration addListener(Class<T> eventType,
             SerializableConsumer<T> method) {
-        List<SerializableConsumer<?>> list = listeners.computeIfAbsent(eventType,
-                key -> new ArrayList<>());
+        List<SerializableConsumer<?>> list = listeners
+                .computeIfAbsent(eventType, key -> new ArrayList<>());
         list.add(method);
         return () -> list.remove(method);
     }
@@ -2188,8 +2196,8 @@ protected <T> Registration addListener(Class<T> eventType,
      * <p>
      * Added listener is notified every time whenever any bound field value is
      * changed, i.e. the UI component value was changed, passed all the
-     * conversions and validations then propagated to the bound bean field. The same
-     * functionality can be achieved by adding a
+     * conversions and validations then propagated to the bound bean field. The
+     * same functionality can be achieved by adding a
      * {@link ValueChangeListener} to all fields in the {@link Binder}.
      * <p>
      * The listener is added to all fields regardless of whether the method is
@@ -2229,9 +2237,13 @@ protected <FIELDVALUE, TARGET> BindingBuilder<BEAN, TARGET> createBinding(
             BindingValidationStatusHandler handler) {
         BindingBuilder<BEAN, TARGET> newBinding = doCreateBinding(field,
                 converter, handler);
-        if (incompleteMemberFieldBindings.containsKey(field)) {
+        if (incompleteMemberFieldBindings != null
+                && incompleteMemberFieldBindings.containsKey(field)) {
             incompleteMemberFieldBindings.put(field, newBinding);
         }
+        if (incompleteBindings == null) {
+            incompleteBindings = new IdentityHashMap<>(8);
+        }
         incompleteBindings.put(field, newBinding);
         return newBinding;
     }
@@ -2468,14 +2480,15 @@ private <FIELDVALUE> Converter<FIELDVALUE, FIELDVALUE> createNullRepresentationA
      *             if this binder has incomplete bindings
      */
     private void checkBindingsCompleted(String methodName) {
-        if (!incompleteMemberFieldBindings.isEmpty()) {
+        if (!(incompleteMemberFieldBindings == null
+                || incompleteMemberFieldBindings.isEmpty())) {
             throw new IllegalStateException(
                     "All bindings created with forMemberField must "
                             + "be completed with bindInstanceFields before calling "
                             + methodName);
         }
 
-        if (!incompleteBindings.isEmpty()) {
+        if (!(incompleteBindings == null || incompleteBindings.isEmpty())) {
             throw new IllegalStateException(
                     "All bindings created with forField must be completed before calling "
                             + methodName);
@@ -2540,7 +2553,8 @@ public void bindInstanceFields(Object objectWithMemberFields) {
                                 memberField, property, type)))
                 .reduce(0, this::accumulate, Integer::sum);
         if (numberOfBoundFields == 0 && bindings.isEmpty()
-                && incompleteBindings.isEmpty()) {
+                && (incompleteBindings == null
+                        || incompleteBindings.isEmpty())) {
             // Throwing here for incomplete bindings would be wrong as they
             // may be completed after this call. If they are not, setBean and
             // other methods will throw for those cases
@@ -2568,6 +2582,9 @@ private int accumulate(int count, boolean value) {
 
     private BindingBuilder<BEAN, ?> getIncompleteMemberFieldBinding(
             Field memberField, Object objectWithMemberFields) {
+        if (incompleteMemberFieldBindings == null) {
+            return null;
+        }
         return incompleteMemberFieldBindings
                 .get(getMemberFieldValue(memberField, objectWithMemberFields));
     }

flow-server/src/main/java/com/vaadin/flow/component/ComponentEventBus.java

@@ -69,7 +69,8 @@ public ListenerWrapper(ComponentEventListener<T> listener) {
     }
 
     // Package private to enable testing only
-    HashMap<Class<? extends ComponentEvent<?>>, ArrayList<ListenerWrapper<?>>> componentEventData = new HashMap<>();
+    HashMap<Class<? extends ComponentEvent<?>>, ArrayList<ListenerWrapper<?>>> componentEventData = new HashMap<>(
+            2);
 
     private Component component;
 

flow-server/src/main/java/com/vaadin/flow/internal/nodefeature/ElementListenerMap.java

@@ -129,9 +129,17 @@ public DomListenerRegistration addEventData(String eventData) {
             }
 
             if (eventDataExpressions == null) {
-                eventDataExpressions = new HashSet<>();
+                eventDataExpressions = Collections.singleton(eventData);
+            } else {
+                if (eventDataExpressions.size() == 1) {
+                    Set<String> oldExpressions = eventDataExpressions;
+                    // Don't use no-args or Collection constructors that
+                    // allocate for 16 entries
+                    eventDataExpressions = new HashSet<>(4);
+                    eventDataExpressions.addAll(oldExpressions);
+                }
+                eventDataExpressions.add(eventData);
             }
-            eventDataExpressions.add(eventData);
 
             listenerMap.updateEventSettings(type);
 
@@ -233,14 +241,22 @@ public DomListenerRegistration add(String eventType,
         assert eventType != null;
         assert listener != null;
 
-        if (listeners == null) {
-            listeners = new HashMap<>();
-        }
-
         if (!contains(eventType)) {
-            assert !listeners.containsKey(eventType);
+            assert listeners == null || !listeners.containsKey(eventType);
+
+            ArrayList<DomEventListenerWrapper> listenerList = new ArrayList<>(
+                    1);
+
+            if (listeners == null) {
+                listeners = Collections.singletonMap(eventType, listenerList);
+            } else {
+                if (listeners.size() == 1 && !(listeners instanceof HashMap)) {
+                    listeners = new HashMap<>(listeners);
+                }
+
+                listeners.put(eventType, listenerList);
+            }
 
-            listeners.put(eventType, new ArrayList<>());
         }
 
         DomEventListenerWrapper listenerWrapper = new DomEventListenerWrapper(
@@ -337,10 +353,10 @@ private void removeListener(String eventType,
 
             // No more listeners of this type?
             if (listenerList.isEmpty()) {
-                listeners.remove(eventType);
-
-                if (listeners.isEmpty()) {
+                if (listeners.size() == 1 && listeners.containsKey(eventType)) {
                     listeners = null;
+                } else {
+                    listeners.remove(eventType);
                 }
 
                 // Remove from the set that is synchronized with the client

flow-server/src/main/java/com/vaadin/flow/internal/nodefeature/ElementPropertyMap.java

@@ -85,8 +85,9 @@ public Runnable deferredUpdateFromClient(String key, Serializable value) {
              */
             if (updateFromClientFilter != null
                     && !updateFromClientFilter.test(key)) {
-                getLogger().warn("Ignoring model update for {}. "
-                        + "For security reasons, the property must have a two-way binding in the template, be annotated with @{} in the model, or be defined as synchronized.",
+                getLogger().warn(
+                        "Ignoring model update for {}. "
+                                + "For security reasons, the property must have a two-way binding in the template, be annotated with @{} in the model, or be defined as synchronized.",
                         key, AllowClientUpdates.class.getSimpleName());
                 return () -> {
                     // nop
@@ -134,11 +135,18 @@ public Registration addPropertyChangeListener(String name,
             PropertyChangeListener listener) {
         assert hasElement();
 
+        List<PropertyChangeListener> propertyListeners;
         if (listeners == null) {
-            listeners = new HashMap<>();
+            propertyListeners = new ArrayList<>(1);
+            listeners = Collections.singletonMap(name, propertyListeners);
+        } else {
+            if (listeners.size() == 1 && !(listeners instanceof HashMap)) {
+                listeners = new HashMap<>(listeners);
+            }
+            propertyListeners = listeners.computeIfAbsent(name,
+                    key -> new ArrayList<>(1));
         }
-        List<PropertyChangeListener> propertyListeners = listeners
-                .computeIfAbsent(name, key -> new ArrayList<>());
+
         propertyListeners.add(listener);
         return () -> propertyListeners.remove(listener);
     }

flow-server/src/main/java/com/vaadin/flow/internal/nodefeature/NodeList.java

@@ -170,7 +170,7 @@ protected int size() {
 
     private void ensureValues() {
         if (values == null) {
-            values = new ArrayList<>();
+            values = new ArrayList<>(1);
         }
     }
 
@@ -329,7 +329,7 @@ public void collectChanges(Consumer<NodeChange> collector) {
 
         if (isRemoveAllCalled && !hasRemoveAll) {
             changes = Stream
-                    .concat(Stream.of(new ListClearChange<T>(this)),
+                    .concat(Stream.of(new ListClearChange<>(this)),
                             allChanges.stream())
                     .filter(this::acceptChange).collect(Collectors.toList());
         } else {
@@ -398,7 +398,7 @@ protected void clear() {
         }
 
         isRemoveAllCalled = true;
-        addChange(new ListClearChange<T>(this));
+        addChange(new ListClearChange<>(this));
     }
 
     /**