Use interface not Implementation, as method parameter

client/src/main/java/com/vaadin/client/JavaScriptConnectorHelper.java

 import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
         return false;
     }
 
-    protected void showInitProblem(ArrayList<String> attemptedNames) {
+    protected void showInitProblem(List<String> attemptedNames) {
         // Default does nothing
     }
 

client/src/main/java/com/vaadin/client/ui/JavaScriptComponentConnector.java

  */
 package com.vaadin.client.ui;
 
+import java.util.List;
+
 import com.google.gwt.user.client.ui.Widget;
 import com.vaadin.client.JavaScriptConnectorHelper;
 import com.vaadin.client.communication.HasJavaScriptConnectorHelper;
             this) {
         @Override
         protected void showInitProblem(
-                java.util.ArrayList<String> attemptedNames) {
+                List<String> attemptedNames) {
             getWidget().showNoInitFound(attemptedNames);
         }
     };

client/src/main/java/com/vaadin/client/ui/JavaScriptWidget.java

  */
 package com.vaadin.client.ui;
 
-import java.util.ArrayList;
+import java.util.List;
 
 import com.google.gwt.dom.client.Document;
 import com.google.gwt.user.client.ui.Widget;
 public class JavaScriptWidget extends Widget {
 
     /**
-     * Creats a JavaScriptWidget based on a <div> element
+     * Creates a JavaScriptWidget based on a <div> element
      */
     public JavaScriptWidget() {
         this("div");
         setElement(Document.get().createElement(tagName));
     }
 
-    public void showNoInitFound(ArrayList<String> attemptedNames) {
+    public void showNoInitFound(List<String> attemptedNames) {
         String message = "Could not initialize JavaScriptConnector because no JavaScript init function was found. Make sure one of these functions are defined: <ul>";
         for (String name : attemptedNames) {
             message += "<li>" + name + "</li>";

client/src/main/java/com/vaadin/client/ui/VUI.java

 
 package com.vaadin.client.ui;
 
-import java.util.ArrayList;
+import java.util.List;
 
 import com.google.gwt.core.client.Scheduler.ScheduledCommand;
 import com.google.gwt.dom.client.Element;
         connection.flushActiveConnector();
     }
 
-    private native static void loadAppIdListFromDOM(ArrayList<String> list)
+    private native static void loadAppIdListFromDOM(List<String> list)
     /*-{
          var j;
          for(j in $wnd.vaadin.vaadinConfigurations) {

client/src/main/java/com/vaadin/client/ui/VWindow.java

         fireOrderEvent(list);
     }
 
-    private static void fireOrderEvent(ArrayList<VWindow> windows) {
+    private static void fireOrderEvent(List<VWindow> windows) {
         WINDOW_ORDER_HANDLER
                 .fireEvent(new WindowOrderEvent(new ArrayList<>(windows)));
     }

client/src/main/java/com/vaadin/client/ui/window/WindowOrderEvent.java

  */
 package com.vaadin.client.ui.window;
 
-import java.util.ArrayList;
+import java.util.List;
 
 import com.google.gwt.event.shared.GwtEvent;
 import com.vaadin.client.ui.VWindow;
 
     private static final Type<WindowOrderHandler> TYPE = new Type<>();
 
-    private final ArrayList<VWindow> windows;
+    private final List<VWindow> windows;
 
     /**
      * Creates a new event with the given order.
      * @param windows
      *            The new order position for the VWindow
      */
-    public WindowOrderEvent(ArrayList<VWindow> windows) {
+    public WindowOrderEvent(List<VWindow> windows) {
         this.windows = windows;
     }
 

server/src/main/java/com/vaadin/ui/UI.java

 
         @Override
         public void windowOrderChanged(
-                HashMap<Integer, Connector> windowOrders) {
+                Map<Integer, Connector> windowOrders) {
             Map<Integer, Window> orders = new LinkedHashMap<>();
             for (Entry<Integer, Connector> entry : windowOrders.entrySet()) {
                 if (entry.getValue() instanceof Window) {

shared/src/main/java/com/vaadin/shared/ui/WindowOrderRpc.java

  */
 package com.vaadin.shared.ui;
 
-import java.util.HashMap;
+import java.util.Map;
 
 import com.vaadin.shared.Connector;
 import com.vaadin.shared.communication.ServerRpc;
      * @param windowOrders
      *            new windows order
      */
-    void windowOrderChanged(HashMap<Integer, Connector> windowOrders);
+    void windowOrderChanged(Map<Integer, Connector> windowOrders);
 }