Use interface instead of implementation (#10073)

25 files changed, 76 insertions, 72 deletions

diff --git a/server/src/main/java/com/vaadin/data/Binder.java b/server/src/main/java/com/vaadin/data/Binder.java
index 0ec15c2345..b57e76571d 100644
--- a/server/src/main/java/com/vaadin/data/Binder.java
+++ b/server/src/main/java/com/vaadin/data/Binder.java
@@ -423,9 +423,11 @@ public class Binder<BEAN> implements Serializable {
                 TARGET nullRepresentation) {
             return withConverter(
                     fieldValue -> Objects.equals(fieldValue, nullRepresentation)
-                            ? null : fieldValue,
+                            ? null
+                            : fieldValue,
                     modelValue -> Objects.isNull(modelValue)
-                            ? nullRepresentation : modelValue);
+                            ? nullRepresentation
+                            : modelValue);
         }
 
         /**
@@ -2157,7 +2159,8 @@ public class Binder<BEAN> implements Serializable {
         Converter<FIELDVALUE, FIELDVALUE> nullRepresentationConverter = Converter
                 .from(fieldValue -> fieldValue,
                         modelValue -> Objects.isNull(modelValue)
-                                ? field.getEmptyValue() : modelValue,
+                                ? field.getEmptyValue()
+                                : modelValue,
                         exception -> exception.getMessage());
         ConverterDelegate<FIELDVALUE> converter = new ConverterDelegate<>(
                 nullRepresentationConverter);
@@ -2382,7 +2385,7 @@ public class Binder<BEAN> implements Serializable {
      * @return list of all fields in the class considering hierarchy
      */
     private List<Field> getFieldsInDeclareOrder(Class<?> searchClass) {
-        ArrayList<Field> memberFieldInOrder = new ArrayList<>();
+        List<Field> memberFieldInOrder = new ArrayList<>();
 
         while (searchClass != null) {
             memberFieldInOrder
diff --git a/server/src/main/java/com/vaadin/event/dd/TargetDetailsImpl.java b/server/src/main/java/com/vaadin/event/dd/TargetDetailsImpl.java
index 3ede6a20e0..0453337c5d 100644
--- a/server/src/main/java/com/vaadin/event/dd/TargetDetailsImpl.java
+++ b/server/src/main/java/com/vaadin/event/dd/TargetDetailsImpl.java
@@ -32,7 +32,7 @@ import com.vaadin.ui.dnd.event.DropEvent;
 @SuppressWarnings("serial")
 public class TargetDetailsImpl implements TargetDetails {
 
-    private HashMap<String, Object> data = new HashMap<>();
+    private Map<String, Object> data = new HashMap<>();
     private DropTarget dropTarget;
 
     protected TargetDetailsImpl(Map<String, Object> rawDropData) {
diff --git a/server/src/main/java/com/vaadin/server/KeyMapper.java b/server/src/main/java/com/vaadin/server/KeyMapper.java
index d20eb7c605..08d36458d3 100644
--- a/server/src/main/java/com/vaadin/server/KeyMapper.java
+++ b/server/src/main/java/com/vaadin/server/KeyMapper.java
@@ -34,9 +34,9 @@ public class KeyMapper<V> implements DataKeyMapper<V>, Serializable {
 
     private int lastKey = 0;
 
-    private final HashMap<Object, String> objectIdKeyMap = new HashMap<>();
+    private final Map<Object, String> objectIdKeyMap = new HashMap<>();
 
-    private final HashMap<String, V> keyObjectMap = new HashMap<>();
+    private final Map<String, V> keyObjectMap = new HashMap<>();
 
     private ValueProvider<V, Object> identifierGetter;
 
diff --git a/server/src/main/java/com/vaadin/server/LegacyCommunicationManager.java b/server/src/main/java/com/vaadin/server/LegacyCommunicationManager.java
index 4524442531..bb8d8cd4d5 100644
--- a/server/src/main/java/com/vaadin/server/LegacyCommunicationManager.java
+++ b/server/src/main/java/com/vaadin/server/LegacyCommunicationManager.java
@@ -59,7 +59,7 @@ import elemental.json.JsonValue;
 public class LegacyCommunicationManager implements Serializable {
 
     // TODO Refactor (#11410)
-    private final HashMap<Integer, ClientCache> uiToClientCache = new HashMap<>();
+    private final Map<Integer, ClientCache> uiToClientCache = new HashMap<>();
 
     /**
      * The session this communication manager is used for
@@ -323,7 +323,7 @@ public class LegacyCommunicationManager implements Serializable {
         }
     }
 
-    private final HashMap<Class<? extends ClientConnector>, Integer> typeToKey = new HashMap<>();
+    private final Map<Class<? extends ClientConnector>, Integer> typeToKey = new HashMap<>();
     private int nextTypeKey = 0;
 
     /**
diff --git a/server/src/main/java/com/vaadin/server/VaadinService.java b/server/src/main/java/com/vaadin/server/VaadinService.java
index ba54ad014f..f4e1972c3e 100644
--- a/server/src/main/java/com/vaadin/server/VaadinService.java
+++ b/server/src/main/java/com/vaadin/server/VaadinService.java
@@ -115,7 +115,8 @@ public abstract class VaadinService implements Serializable {
     private static final String REQUEST_START_TIME_ATTRIBUTE = "requestStartTime";
 
     /**
-     * Should never be used directly, always use {@link #getDeploymentConfiguration()}
+     * Should never be used directly, always use
+     * {@link #getDeploymentConfiguration()}
      */
     private final DeploymentConfiguration deploymentConfiguration;
 
@@ -265,7 +266,7 @@ public abstract class VaadinService implements Serializable {
      */
     protected List<RequestHandler> createRequestHandlers()
             throws ServiceException {
-        ArrayList<RequestHandler> handlers = new ArrayList<>();
+        List<RequestHandler> handlers = new ArrayList<>();
         handlers.add(new SessionRequestHandler());
         handlers.add(new PublishedFileHandler());
         handlers.add(new HeartbeatHandler());
@@ -375,8 +376,7 @@ public abstract class VaadinService implements Serializable {
 
     /**
      * Gets the deployment configuration. Should be overridden (or otherwise
-     * intercepted) if the no-arg constructor is used in order to prevent
-     * NPEs.
+     * intercepted) if the no-arg constructor is used in order to prevent NPEs.
      *
      * @return the deployment configuration
      */
@@ -530,7 +530,7 @@ public abstract class VaadinService implements Serializable {
             if (session.getState() == State.OPEN) {
                 closeSession(session);
             }
-            ArrayList<UI> uis = new ArrayList<>(session.getUIs());
+            List<UI> uis = new ArrayList<>(session.getUIs());
             for (final UI ui : uis) {
                 ui.accessSynchronously(() -> {
                     /*
@@ -1126,8 +1126,7 @@ public abstract class VaadinService implements Serializable {
         // Stores all attributes (security key, reference to this context
         // instance) so they can be added to the new session
         Set<String> attributeNames = oldSession.getAttributeNames();
-        HashMap<String, Object> attrs = new HashMap<>(
-                attributeNames.size() * 2);
+        Map<String, Object> attrs = new HashMap<>(attributeNames.size() * 2);
         for (String name : attributeNames) {
             Object value = oldSession.getAttribute(name);
             if (value instanceof VaadinSession) {
@@ -1266,7 +1265,7 @@ public abstract class VaadinService implements Serializable {
      * @param session
      */
     private void removeClosedUIs(final VaadinSession session) {
-        ArrayList<UI> uis = new ArrayList<>(session.getUIs());
+        List<UI> uis = new ArrayList<>(session.getUIs());
         for (final UI ui : uis) {
             if (ui.isClosing()) {
                 ui.accessSynchronously(() -> {
diff --git a/server/src/main/java/com/vaadin/server/communication/ServerRpcHandler.java b/server/src/main/java/com/vaadin/server/communication/ServerRpcHandler.java
index f2caf5631c..38c7e4db5f 100644
--- a/server/src/main/java/com/vaadin/server/communication/ServerRpcHandler.java
+++ b/server/src/main/java/com/vaadin/server/communication/ServerRpcHandler.java
@@ -501,8 +501,7 @@ public class ServerRpcHandler implements Serializable {
             ConnectorTracker connectorTracker, JsonArray invocationsJson,
             int lastSyncIdSeenByClient) {
         int invocationCount = invocationsJson.length();
-        ArrayList<MethodInvocation> invocations = new ArrayList<>(
-                invocationCount);
+        List<MethodInvocation> invocations = new ArrayList<>(invocationCount);
 
         MethodInvocation previousInvocation = null;
         // parse JSON to MethodInvocations
diff --git a/server/src/main/java/com/vaadin/server/communication/SessionRequestHandler.java b/server/src/main/java/com/vaadin/server/communication/SessionRequestHandler.java
index 3700e67c36..18c1135dee 100644
--- a/server/src/main/java/com/vaadin/server/communication/SessionRequestHandler.java
+++ b/server/src/main/java/com/vaadin/server/communication/SessionRequestHandler.java
@@ -17,6 +17,7 @@ package com.vaadin.server.communication;
 
 import java.io.IOException;
 import java.util.ArrayList;
+import java.util.List;
 
 import com.vaadin.server.RequestHandler;
 import com.vaadin.server.VaadinRequest;
@@ -52,7 +53,7 @@ public class SessionRequestHandler implements RequestHandler {
             VaadinResponse response) throws IOException {
         // Use a copy to avoid ConcurrentModificationException
         session.lock();
-        ArrayList<RequestHandler> requestHandlers;
+        List<RequestHandler> requestHandlers;
         try {
             requestHandlers = new ArrayList<>(session.getRequestHandlers());
         } finally {
diff --git a/server/src/main/java/com/vaadin/server/communication/UidlWriter.java b/server/src/main/java/com/vaadin/server/communication/UidlWriter.java
index 92b6e8e8bd..cdcb587b01 100644
--- a/server/src/main/java/com/vaadin/server/communication/UidlWriter.java
+++ b/server/src/main/java/com/vaadin/server/communication/UidlWriter.java
@@ -89,7 +89,7 @@ public class UidlWriter implements Serializable {
         getLogger().log(Level.FINE, "* Creating response to client");
 
         while (true) {
-            ArrayList<ClientConnector> connectorsToProcess = new ArrayList<>();
+            List<ClientConnector> connectorsToProcess = new ArrayList<>();
             for (ClientConnector c : uiConnectorTracker
                     .getDirtyVisibleConnectors()) {
                 if (!processedConnectors.contains(c)) {
@@ -138,7 +138,8 @@ public class UidlWriter implements Serializable {
 
             int syncId = service.getDeploymentConfiguration()
                     .isSyncIdCheckEnabled()
-                            ? uiConnectorTracker.getCurrentSyncId() : -1;
+                            ? uiConnectorTracker.getCurrentSyncId()
+                            : -1;
             writer.write("\"" + ApplicationConstants.SERVER_SYNC_ID + "\": "
                     + syncId + ", ");
             if (repaintAll) {
diff --git a/server/src/main/java/com/vaadin/server/widgetsetutils/ClassPathExplorer.java b/server/src/main/java/com/vaadin/server/widgetsetutils/ClassPathExplorer.java
index f93803de99..65e3413122 100644
--- a/server/src/main/java/com/vaadin/server/widgetsetutils/ClassPathExplorer.java
+++ b/server/src/main/java/com/vaadin/server/widgetsetutils/ClassPathExplorer.java
@@ -58,8 +58,8 @@ public class ClassPathExplorer {
     /**
      * File filter that only accepts directories.
      */
-    private static final FileFilter DIRECTORIES_ONLY = (File f) ->
-            f.exists() && f.isDirectory();
+    private static final FileFilter DIRECTORIES_ONLY = (File f) -> f.exists()
+            && f.isDirectory();
 
     /**
      * Contains information about widgetsets and themes found on the classpath
@@ -525,7 +525,7 @@ public class ClassPathExplorer {
     public static URL getWidgetsetSourceDirectory(String widgetsetFileName) {
         if (debug) {
             debug("classpathLocations values:");
-            ArrayList<String> locations = new ArrayList<>(
+            List<String> locations = new ArrayList<>(
                     classpathLocations.keySet());
             for (String location : locations) {
                 debug(String.valueOf(classpathLocations.get(location)));
diff --git a/server/src/main/java/com/vaadin/ui/AbstractComponent.java b/server/src/main/java/com/vaadin/ui/AbstractComponent.java
index f74f2141da..2c9c40e668 100644
--- a/server/src/main/java/com/vaadin/ui/AbstractComponent.java
+++ b/server/src/main/java/com/vaadin/ui/AbstractComponent.java
@@ -427,7 +427,7 @@ public abstract class AbstractComponent extends AbstractClientConnector
             return false;
         }
         return !(getParent() instanceof SelectiveRenderer)
-            || ((SelectiveRenderer) getParent()).isRendered(this);
+                || ((SelectiveRenderer) getParent()).isRendered(this);
     }
 
     /*
@@ -1251,7 +1251,7 @@ public abstract class AbstractComponent extends AbstractClientConnector
      *         implementation
      */
     protected Collection<String> getCustomAttributes() {
-        ArrayList<String> l = new ArrayList<>(Arrays.asList(customAttributes));
+        List<String> l = new ArrayList<>(Arrays.asList(customAttributes));
         if (this instanceof Focusable) {
             l.add("tab-index");
             l.add("tabindex");
@@ -1259,10 +1259,10 @@ public abstract class AbstractComponent extends AbstractClientConnector
         return l;
     }
 
-    private static final String[] customAttributes = { "width",
-            "height", "debug-id", "error", "width-auto", "height-auto",
-            "width-full", "height-full", "size-auto", "size-full", "immediate",
-            "locale", "read-only", "_id" };
+    private static final String[] customAttributes = { "width", "height",
+            "debug-id", "error", "width-auto", "height-auto", "width-full",
+            "height-full", "size-auto", "size-full", "immediate", "locale",
+            "read-only", "_id" };
 
     /*
      * (non-Javadoc)
@@ -1288,9 +1288,11 @@ public abstract class AbstractComponent extends AbstractClientConnector
         writeSize(attr, def);
         // handle component error
         String errorMsg = getComponentError() != null
-                ? getComponentError().getFormattedHtmlMessage() : null;
+                ? getComponentError().getFormattedHtmlMessage()
+                : null;
         String defErrorMsg = def.getComponentError() != null
-                ? def.getComponentError().getFormattedHtmlMessage() : null;
+                ? def.getComponentError().getFormattedHtmlMessage()
+                : null;
         if (!SharedUtil.equals(errorMsg, defErrorMsg)) {
             attr.put("error", errorMsg);
         }
diff --git a/server/src/main/java/com/vaadin/ui/AbstractMedia.java b/server/src/main/java/com/vaadin/ui/AbstractMedia.java
index 800f5dca31..b83f25acc4 100644
--- a/server/src/main/java/com/vaadin/ui/AbstractMedia.java
+++ b/server/src/main/java/com/vaadin/ui/AbstractMedia.java
@@ -153,7 +153,7 @@ public abstract class AbstractMedia extends AbstractComponent {
      * @return The sources pointed to in this media.
      */
     public List<Resource> getSources() {
-        ArrayList<Resource> sources = new ArrayList<>();
+        List<Resource> sources = new ArrayList<>();
         for (URLReference ref : getState(false).sources) {
             sources.add(((ResourceReference) ref).getResource());
         }
diff --git a/server/src/main/java/com/vaadin/ui/ConnectorTracker.java b/server/src/main/java/com/vaadin/ui/ConnectorTracker.java
index 1bd9f81892..7b6002008d 100644
--- a/server/src/main/java/com/vaadin/ui/ConnectorTracker.java
+++ b/server/src/main/java/com/vaadin/ui/ConnectorTracker.java
@@ -67,7 +67,7 @@ import elemental.json.JsonObject;
  */
 public class ConnectorTracker implements Serializable {
 
-    private final HashMap<String, ClientConnector> connectorIdToConnector = new HashMap<>();
+    private final Map<String, ClientConnector> connectorIdToConnector = new HashMap<>();
     private final Set<ClientConnector> dirtyConnectors = new HashSet<>();
     private final Set<ClientConnector> uninitializedConnectors = new HashSet<>();
 
@@ -729,12 +729,11 @@ public class ConnectorTracker implements Serializable {
     }
 
     /* Special serialization to JsonObjects which are not serializable */
-    private void writeObject(ObjectOutputStream out)
-            throws IOException {
+    private void writeObject(ObjectOutputStream out) throws IOException {
         out.defaultWriteObject();
         // Convert JsonObjects in diff state to String representation as
         // JsonObject is not serializable
-        HashMap<ClientConnector, String> stringDiffStates = new HashMap<>(
+        Map<ClientConnector, String> stringDiffStates = new HashMap<>(
                 diffStates.size() * 2);
         for (ClientConnector key : diffStates.keySet()) {
             stringDiffStates.put(key, diffStates.get(key).toString());
@@ -751,7 +750,7 @@ public class ConnectorTracker implements Serializable {
         // JsonObject is not serializable
         diffStates = new HashMap<>();
         @SuppressWarnings("unchecked")
-        HashMap<ClientConnector, String> stringDiffStates = (HashMap<ClientConnector, String>) in
+        Map<ClientConnector, String> stringDiffStates = (HashMap<ClientConnector, String>) in
                 .readObject();
         diffStates = new HashMap<>(stringDiffStates.size() * 2);
         for (ClientConnector key : stringDiffStates.keySet()) {
diff --git a/server/src/main/java/com/vaadin/ui/CustomLayout.java b/server/src/main/java/com/vaadin/ui/CustomLayout.java
index d44a02f52e..76107d7992 100644
--- a/server/src/main/java/com/vaadin/ui/CustomLayout.java
+++ b/server/src/main/java/com/vaadin/ui/CustomLayout.java
@@ -73,7 +73,7 @@ public class CustomLayout extends AbstractLayout implements LegacyComponent {
     /**
      * Custom layout slots containing the components.
      */
-    private final HashMap<String, Component> slots = new HashMap<>();
+    private final Map<String, Component> slots = new HashMap<>();
 
     /**
      * Default constructor only used by subclasses. Subclasses are responsible
diff --git a/server/src/main/java/com/vaadin/ui/Flash.java b/server/src/main/java/com/vaadin/ui/Flash.java
index ced6d0bbad..affda1a372 100644
--- a/server/src/main/java/com/vaadin/ui/Flash.java
+++ b/server/src/main/java/com/vaadin/ui/Flash.java
@@ -18,6 +18,7 @@ package com.vaadin.ui;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import org.jsoup.nodes.Element;
@@ -238,7 +239,7 @@ public class Flash extends AbstractEmbedded {
         super.writeDesign(design, designContext);
 
         // Parameters, in alphabetic order
-        ArrayList<String> paramNames = new ArrayList<>();
+        List<String> paramNames = new ArrayList<>();
         for (String param : getParameterNames()) {
             paramNames.add(param);
         }
diff --git a/server/src/main/java/com/vaadin/ui/LoginForm.java b/server/src/main/java/com/vaadin/ui/LoginForm.java
index 01f64665bd..771e353f3e 100644
--- a/server/src/main/java/com/vaadin/ui/LoginForm.java
+++ b/server/src/main/java/com/vaadin/ui/LoginForm.java
@@ -345,7 +345,7 @@ public class LoginForm extends AbstractSingleComponentContainer {
      * URL in the method or the password manager will not be triggered.
      */
     private void login() {
-        HashMap<String, String> params = new HashMap<>();
+        Map<String, String> params = new HashMap<>();
         params.put("username", getUsernameField().getValue());
         params.put("password", getPasswordField().getValue());
         LoginEvent event = new LoginEvent(LoginForm.this, params);
diff --git a/server/src/main/java/com/vaadin/ui/TabSheet.java b/server/src/main/java/com/vaadin/ui/TabSheet.java
index ac3a22eb41..8cbd41ccc2 100644
--- a/server/src/main/java/com/vaadin/ui/TabSheet.java
+++ b/server/src/main/java/com/vaadin/ui/TabSheet.java
@@ -110,7 +110,7 @@ public class TabSheet extends AbstractComponentContainer
     /**
      * Map containing information related to the tabs (caption, icon etc).
      */
-    private final HashMap<Component, Tab> tabs = new HashMap<>();
+    private final Map<Component, Tab> tabs = new HashMap<>();
 
     /**
      * Selected tab content component.
@@ -1323,7 +1323,6 @@ public class TabSheet extends AbstractComponentContainer
                 tabState.componentErrorLevel = null;
             }
 
-
             markAsDirty();
         }
 
diff --git a/server/src/main/java/com/vaadin/ui/UI.java b/server/src/main/java/com/vaadin/ui/UI.java
index e8b9198111..5c89c7f040 100644
--- a/server/src/main/java/com/vaadin/ui/UI.java
+++ b/server/src/main/java/com/vaadin/ui/UI.java
@@ -457,7 +457,7 @@ public abstract class UI extends AbstractSingleComponentContainer
     public Iterator<Component> iterator() {
         // TODO could directly create some kind of combined iterator instead of
         // creating a new ArrayList
-        ArrayList<Component> components = new ArrayList<>();
+        List<Component> components = new ArrayList<>();
 
         if (getContent() != null) {
             components.add(getContent());
diff --git a/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java b/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java
index 5b5887316c..357a9fbdf3 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java
@@ -449,7 +449,7 @@ public class DesignAttributeHandler implements Serializable {
         }
 
         private Collection<String> getAttributes() {
-            ArrayList<String> attributes = new ArrayList<>();
+            List<String> attributes = new ArrayList<>();
             attributes.addAll(accessMethods.keySet());
             return attributes;
         }
diff --git a/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java b/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java
index dfd7033430..aedd33618e 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java
@@ -248,7 +248,7 @@ public class FieldBinder implements Serializable {
      */
     protected static List<java.lang.reflect.Field> getFields(
             Class<?> searchClass) {
-        ArrayList<java.lang.reflect.Field> memberFields = new ArrayList<>();
+        List<java.lang.reflect.Field> memberFields = new ArrayList<>();
 
         memberFields.addAll(Arrays.asList(searchClass.getDeclaredFields()));
         return memberFields;
diff --git a/server/src/main/java/com/vaadin/ui/declarative/converters/DesignShortcutActionConverter.java b/server/src/main/java/com/vaadin/ui/declarative/converters/DesignShortcutActionConverter.java
index 63f509c9ce..a1c283fae0 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/converters/DesignShortcutActionConverter.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/converters/DesignShortcutActionConverter.java
@@ -40,7 +40,7 @@ public class DesignShortcutActionConverter
     private final Map<String, Integer> presentationMap;
 
     public DesignShortcutActionConverter() {
-        HashMap<Integer, String> codes = new HashMap<>();
+        Map<Integer, String> codes = new HashMap<>();
         // map modifiers
         codes.put(ModifierKey.ALT, "alt");
         codes.put(ModifierKey.CTRL, "ctrl");
@@ -112,7 +112,7 @@ public class DesignShortcutActionConverter
 
         keyCodeMap = Collections.unmodifiableMap(codes);
 
-        HashMap<String, Integer> presentations = new HashMap<>();
+        Map<String, Integer> presentations = new HashMap<>();
         for (Entry<Integer, String> entry : keyCodeMap.entrySet()) {
             presentations.put(entry.getValue(), entry.getKey());
         }
diff --git a/server/src/test/java/com/vaadin/server/JSONSerializerTest.java b/server/src/test/java/com/vaadin/server/JSONSerializerTest.java
index ec5ba8bfc8..250d6831f4 100644
--- a/server/src/test/java/com/vaadin/server/JSONSerializerTest.java
+++ b/server/src/test/java/com/vaadin/server/JSONSerializerTest.java
@@ -40,8 +40,8 @@ import elemental.json.JsonValue;
  *
  */
 public class JSONSerializerTest {
-    HashMap<String, AbstractSplitPanelState> stringToStateMap;
-    HashMap<AbstractSplitPanelState, String> stateToStringMap;
+    Map<String, AbstractSplitPanelState> stringToStateMap;
+    Map<AbstractSplitPanelState, String> stateToStringMap;
 
     @Test
     public void testStringToBeanMapSerialization() throws Exception {
diff --git a/server/src/test/java/com/vaadin/tests/design/DeclarativeTestBaseBase.java b/server/src/test/java/com/vaadin/tests/design/DeclarativeTestBaseBase.java
index 609ec6d620..323238266e 100644
--- a/server/src/test/java/com/vaadin/tests/design/DeclarativeTestBaseBase.java
+++ b/server/src/test/java/com/vaadin/tests/design/DeclarativeTestBaseBase.java
@@ -268,7 +268,7 @@ public abstract class DeclarativeTestBaseBase<T extends Component> {
      */
     private String elementToHtml(Element producedElem, StringBuilder sb) {
         HashSet<String> booleanAttributes = new HashSet<>();
-        ArrayList<String> names = new ArrayList<>();
+        List<String> names = new ArrayList<>();
         for (Attribute a : producedElem.attributes().asList()) {
             names.add(a.getKey());
             if (a instanceof BooleanAttribute) {
diff --git a/server/src/test/java/com/vaadin/tests/server/ClassesSerializableTest.java b/server/src/test/java/com/vaadin/tests/server/ClassesSerializableTest.java
index 085c0ec348..c42a11e31d 100644
--- a/server/src/test/java/com/vaadin/tests/server/ClassesSerializableTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/ClassesSerializableTest.java
@@ -101,9 +101,8 @@ public class ClassesSerializableTest {
             "com\\.vaadin\\.themes\\.valoutil\\.BodyStyleName", //
             "com\\.vaadin\\.server\\.communication\\.JSR356WebsocketInitializer.*", //
             "com\\.vaadin\\.screenshotbrowser\\.ScreenshotBrowser.*", //
-            "com\\.vaadin\\.osgi.*",//
-            "com\\.vaadin\\.server\\.osgi.*"
-    };
+            "com\\.vaadin\\.osgi.*", //
+            "com\\.vaadin\\.server\\.osgi.*" };
 
     /**
      * Tests that all the relevant classes and interfaces under
@@ -120,9 +119,9 @@ public class ClassesSerializableTest {
             classes.addAll(findServerClasses(location));
         }
 
-        ArrayList<Field> nonSerializableFunctionFields = new ArrayList<>();
+        List<Field> nonSerializableFunctionFields = new ArrayList<>();
 
-        ArrayList<Class<?>> nonSerializableClasses = new ArrayList<>();
+        List<Class<?>> nonSerializableClasses = new ArrayList<>();
         for (String className : classes) {
             Class<?> cls = Class.forName(className);
             // Don't add classes that have a @Ignore annotation on the class
@@ -209,7 +208,7 @@ public class ClassesSerializableTest {
     }
 
     private void failSerializableFields(
-            ArrayList<Field> nonSerializableFunctionFields) {
+            List<Field> nonSerializableFunctionFields) {
         String nonSerializableString = nonSerializableFunctionFields.stream()
                 .map(field -> String.format("%s.%s",
                         field.getDeclaringClass().getName(), field.getName()))
@@ -220,7 +219,7 @@ public class ClassesSerializableTest {
     }
 
     private void failSerializableClasses(
-            ArrayList<Class<?>> nonSerializableClasses) {
+            List<Class<?>> nonSerializableClasses) {
         String nonSerializableString = "";
         Iterator<Class<?>> it = nonSerializableClasses.iterator();
         while (it.hasNext()) {
diff --git a/server/src/test/java/com/vaadin/tests/server/KeyMapperTest.java b/server/src/test/java/com/vaadin/tests/server/KeyMapperTest.java
index 47a81aa8e4..b404ac2386 100644
--- a/server/src/test/java/com/vaadin/tests/server/KeyMapperTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/KeyMapperTest.java
@@ -1,16 +1,18 @@
 package com.vaadin.tests.server;
 
-import com.vaadin.server.KeyMapper;
-import org.junit.Test;
-
-import java.lang.reflect.Field;
-import java.util.HashMap;
-
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotSame;
 import static org.junit.Assert.assertSame;
 import static org.junit.Assert.fail;
 
+import java.lang.reflect.Field;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.Test;
+
+import com.vaadin.server.KeyMapper;
+
 public class KeyMapperTest {
 
     @Test
@@ -104,8 +106,8 @@ public class KeyMapperTest {
             f1.setAccessible(true);
             f2.setAccessible(true);
 
-            HashMap<?, ?> h1 = (HashMap<?, ?>) f1.get(mapper);
-            HashMap<?, ?> h2 = (HashMap<?, ?>) f2.get(mapper);
+            Map<?, ?> h1 = (HashMap<?, ?>) f1.get(mapper);
+            Map<?, ?> h2 = (HashMap<?, ?>) f2.get(mapper);
 
             assertEquals(i, h1.size());
             assertEquals(i, h2.size());
diff --git a/server/src/test/java/com/vaadin/tests/server/component/datefield/ResolutionTest.java b/server/src/test/java/com/vaadin/tests/server/component/datefield/ResolutionTest.java
index 0db8fbe86f..c2e453271a 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/datefield/ResolutionTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/datefield/ResolutionTest.java
@@ -1,6 +1,7 @@
 package com.vaadin.tests.server.component.datefield;
 
 import java.util.ArrayList;
+import java.util.List;
 
 import org.junit.Test;
 
@@ -13,7 +14,7 @@ public class ResolutionTest {
     public void testResolutionHigherOrEqualToYear() {
         Iterable<DateResolution> higherOrEqual = DateResolution
                 .getResolutionsHigherOrEqualTo(DateResolution.YEAR);
-        ArrayList<DateResolution> expected = new ArrayList<>();
+        List<DateResolution> expected = new ArrayList<>();
         expected.add(DateResolution.YEAR);
         TestUtil.assertIterableEquals(expected, higherOrEqual);
     }
@@ -22,22 +23,20 @@ public class ResolutionTest {
     public void testResolutionHigherOrEqualToDay() {
         Iterable<DateResolution> higherOrEqual = DateResolution
                 .getResolutionsHigherOrEqualTo(DateResolution.DAY);
-        ArrayList<DateResolution> expected = new ArrayList<>();
+        List<DateResolution> expected = new ArrayList<>();
         expected.add(DateResolution.DAY);
         expected.add(DateResolution.MONTH);
         expected.add(DateResolution.YEAR);
         TestUtil.assertIterableEquals(expected, higherOrEqual);
-
     }
 
     @Test
     public void testResolutionLowerThanYear() {
         Iterable<DateResolution> higherOrEqual = DateResolution
                 .getResolutionsLowerThan(DateResolution.YEAR);
-        ArrayList<DateResolution> expected = new ArrayList<>();
+        List<DateResolution> expected = new ArrayList<>();
         expected.add(DateResolution.MONTH);
         expected.add(DateResolution.DAY);
         TestUtil.assertIterableEquals(expected, higherOrEqual);
-
     }
 }