diff --git a/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/desktop/DesktopTaskListView.java b/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/desktop/DesktopTaskListView.java
index 69fac21..81ac60a 100644
--- a/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/desktop/DesktopTaskListView.java
+++ b/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/desktop/DesktopTaskListView.java
@@ -22,7 +22,7 @@
 import com.google.gwt.user.cellview.client.DataGrid;
 import com.google.gwt.user.cellview.client.HasKeyboardSelectionPolicy.KeyboardSelectionPolicy;
 import com.google.gwt.user.cellview.client.TextColumn;
-import com.google.gwt.user.client.ui.ResizeComposite;
+import com.google.gwt.user.client.ui.RequiresResizeComposite;
 import com.google.gwt.view.client.NoSelectionModel;
 import com.google.gwt.view.client.SelectionChangeEvent;
 import com.google.gwt.view.client.SelectionModel;
@@ -33,7 +33,7 @@
 /**
  * View used to display the list of Tasks.
  */
-public class DesktopTaskListView extends ResizeComposite implements TaskListView {
+public class DesktopTaskListView extends RequiresResizeComposite<DataGrid<?>> implements TaskListView {
 
   /**
    * Displays the list of tasks.
diff --git a/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/desktop/MobileWebAppShellDesktop.java b/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/desktop/MobileWebAppShellDesktop.java
index 117dfec..f8e8842 100644
--- a/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/desktop/MobileWebAppShellDesktop.java
+++ b/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/desktop/MobileWebAppShellDesktop.java
@@ -49,7 +49,7 @@
 import com.google.gwt.user.client.ui.IsWidget;
 import com.google.gwt.user.client.ui.Label;
 import com.google.gwt.user.client.ui.PopupPanel;
-import com.google.gwt.user.client.ui.ResizeComposite;
+import com.google.gwt.user.client.ui.RequiresResizeComposite;
 import com.google.gwt.user.client.ui.VerticalPanel;
 import com.google.gwt.user.client.ui.Widget;
 import com.google.gwt.view.client.SelectionChangeEvent;
@@ -63,7 +63,7 @@
 /**
  * Desktop version of the UI shell.
  */
-public class MobileWebAppShellDesktop extends ResizeComposite implements MobileWebAppShell {
+public class MobileWebAppShellDesktop extends RequiresResizeComposite<DockLayoutPanel> implements MobileWebAppShell {
 
   /**
    * CSS override used for the main menu.
@@ -71,7 +71,7 @@
   interface MainMenuStyle extends CellList.Style {
   }
 
-  interface MobileWebAppShellDesktopUiBinder extends UiBinder<Widget, MobileWebAppShellDesktop> {
+  interface MobileWebAppShellDesktopUiBinder extends UiBinder<DockLayoutPanel, MobileWebAppShellDesktop> {
   }
 
   /**
@@ -147,7 +147,6 @@
 
   /**
    * Construct a new {@link MobileWebAppShellDesktop}.
-   * @param clientFactory the {@link ClientFactory} of shared resources
    */
   public MobileWebAppShellDesktop(EventBus bus, final PlaceController placeController,
       TaskListView taskListView, TaskEditView taskEditView, TaskReadView taskReadView) {
diff --git a/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/mobile/MobileWebAppShellMobile.java b/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/mobile/MobileWebAppShellMobile.java
index 1521ba6..41e11e0 100644
--- a/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/mobile/MobileWebAppShellMobile.java
+++ b/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/mobile/MobileWebAppShellMobile.java
@@ -36,15 +36,15 @@
 import com.google.gwt.user.client.ui.DeckLayoutPanel;
 import com.google.gwt.user.client.ui.IsWidget;
 import com.google.gwt.user.client.ui.LayoutPanel;
-import com.google.gwt.user.client.ui.ResizeComposite;
+import com.google.gwt.user.client.ui.RequiresResizeComposite;
 import com.google.gwt.user.client.ui.Widget;
 
 /**
  * Mobile version of the UI shell.
  */
-public class MobileWebAppShellMobile extends ResizeComposite implements MobileWebAppShell {
+public class MobileWebAppShellMobile extends RequiresResizeComposite<LayoutPanel> implements MobileWebAppShell {
 
-  interface MobileWebAppShellMobileUiBinder extends UiBinder<Widget, MobileWebAppShellMobile> {
+  interface MobileWebAppShellMobileUiBinder extends UiBinder<LayoutPanel, MobileWebAppShellMobile> {
   }
 
   private static MobileWebAppShellMobileUiBinder uiBinder =
diff --git a/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/tablet/MobileWebAppShellTablet.java b/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/tablet/MobileWebAppShellTablet.java
index e98b290..9ede378 100644
--- a/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/tablet/MobileWebAppShellTablet.java
+++ b/samples/mobilewebapp/src/main/java/com/google/gwt/sample/mobilewebapp/client/tablet/MobileWebAppShellTablet.java
@@ -34,7 +34,7 @@
 import com.google.gwt.user.client.ui.DockLayoutPanel;
 import com.google.gwt.user.client.ui.IsWidget;
 import com.google.gwt.user.client.ui.Label;
-import com.google.gwt.user.client.ui.ResizeComposite;
+import com.google.gwt.user.client.ui.RequiresResizeComposite;
 import com.google.gwt.user.client.ui.SimplePanel;
 import com.google.gwt.user.client.ui.Widget;
 
@@ -43,9 +43,9 @@
  * 
  * TODO(rjrjr): this thing needs a presenter. Not an activity. A presenter.
  */
-public class MobileWebAppShellTablet extends ResizeComposite implements MobileWebAppShell {
+public class MobileWebAppShellTablet extends RequiresResizeComposite<DockLayoutPanel> implements MobileWebAppShell {
 
-  interface MobileWebAppShellTabletUiBinder extends UiBinder<Widget, MobileWebAppShellTablet> {
+  interface MobileWebAppShellTabletUiBinder extends UiBinder<DockLayoutPanel, MobileWebAppShellTablet> {
   }
 
   private static MobileWebAppShellTabletUiBinder uiBinder =
diff --git a/tools/api-checker/config/gwt23_24userApi.conf b/tools/api-checker/config/gwt23_24userApi.conf
index 595e1e1..741d26a 100644
--- a/tools/api-checker/config/gwt23_24userApi.conf
+++ b/tools/api-checker/config/gwt23_24userApi.conf
@@ -157,3 +157,11 @@
 com.google.gwt.user.client.ui.Image::prefetch(Ljava/lang/String;) OVERLOADED_METHOD_CALL
 com.google.gwt.user.client.ui.Image::setUrl(Ljava/lang/String;) OVERLOADED_METHOD_CALL
 com.google.gwt.user.client.ui.Image::setUrlAndVisibleRect(Ljava/lang/String;IIII) OVERLOADED_METHOD_CALL
+
+# Change StackLayoutPanel and TabLayoutPanel to get new superclass
+com.google.gwt.user.client.ui.StackLayoutPanel::getWidget() OVERRIDABLE_METHOD_RETURN_TYPE_CHANGE  from class com.google.gwt.user.client.ui.Widget to class com.google.gwt.user.client.ui.LayoutPanel
+com.google.gwt.user.client.ui.StackLayoutPanel::initWidget(Lcom/google/gwt/user/client/ui/Widget;) MISSING
+com.google.gwt.user.client.ui.StackLayoutPanel::setWidget(Lcom/google/gwt/user/client/ui/Widget;) MISSING
+com.google.gwt.user.client.ui.TabLayoutPanel::getWidget() OVERRIDABLE_METHOD_RETURN_TYPE_CHANGE  from class com.google.gwt.user.client.ui.Widget to class com.google.gwt.user.client.ui.LayoutPanel
+com.google.gwt.user.client.ui.TabLayoutPanel::initWidget(Lcom/google/gwt/user/client/ui/Widget;) MISSING
+com.google.gwt.user.client.ui.TabLayoutPanel::setWidget(Lcom/google/gwt/user/client/ui/Widget;) MISSING
diff --git a/user/src/com/google/gwt/user/client/ui/AbstractComposite.java b/user/src/com/google/gwt/user/client/ui/AbstractComposite.java
new file mode 100644
index 0000000..2195ac4
--- /dev/null
+++ b/user/src/com/google/gwt/user/client/ui/AbstractComposite.java
@@ -0,0 +1,134 @@
+/*
+ * Copyright 2011 Google Inc.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.gwt.user.client.ui;
+
+import com.google.gwt.event.logical.shared.AttachEvent;
+import com.google.gwt.user.client.DOM;
+import com.google.gwt.user.client.Event;
+
+/**
+ * A type of widget that can wrap another widget, hiding the wrapped widget's
+ * methods. When added to a panel, a composite behaves exactly as if the widget
+ * it wraps had been added.
+ * <p>
+ * The composite is useful for creating a single widget out of an aggregate of
+ * multiple other widgets contained in a single panel.
+ * 
+ * @see Composite
+ * 
+ * @param <W> the type of IsWidget this composite wraps
+ */
+public class AbstractComposite<W extends IsWidget> extends Widget {
+
+  private W isWidget;
+
+  @Override
+  public boolean isAttached() {
+    if (isWidget != null) {
+      return isWidget.asWidget().isAttached();
+    }
+    return false;
+  }
+
+  @Override
+  public void onBrowserEvent(Event event) {
+    // Fire any handler added to the composite itself.
+    super.onBrowserEvent(event);
+
+    // Delegate events to the widget.
+    getWidget().asWidget().onBrowserEvent(event);
+  }
+
+  /**
+   * Provides subclasses access to the widget that defines this composite.
+   * 
+   * @return the widget
+   */
+  protected W getWidget() {
+    return isWidget;
+  }
+
+  /**
+   * Sets the widget to be wrapped by the composite. The wrapped widget must be
+   * set before calling any {@link Widget} methods on this object, or adding it
+   * to a panel. This method may only be called once for a given composite.
+   * <p>
+   * The widget returned by the wrapped object's {@link IsWidget#asWidget()} method
+   * must be stable. If it changes, the results are unpredictable.
+   * 
+   * @param isWidget the widget to be wrapped
+   */
+  protected void initWidget(W isWidget) {
+    // Validate. Make sure the widget is not being set twice.
+    if (this.isWidget != null) {
+      throw new IllegalStateException("initWidget() may only be called once.");
+    }
+
+    // TODO rjrjr: avoids breaking some mocked unit tests, should fix the tests instead
+    Widget newChild = isWidget instanceof Widget ? (Widget) isWidget : isWidget.asWidget();
+
+    // Detach the new child.
+    newChild.removeFromParent();
+
+    // Use the contained widget's element as the composite's element,
+    // effectively merging them within the DOM.
+    setElement(newChild.getElement());
+
+    // Logical attach.
+    this.isWidget = isWidget;
+
+    // Adopt.
+    newChild.setParent(this);
+  }
+
+  /**
+   * 
+   */
+  @Override
+  protected void onAttach() {
+    Widget asWidget = getWidget().asWidget();
+
+    if (!isOrWasAttached()) {
+      asWidget.sinkEvents(eventsToSink);
+      eventsToSink = -1;
+    }
+
+    asWidget.onAttach();
+
+    // Clobber the widget's call to setEventListener(), causing all events to
+    // be routed to this composite, which will delegate back to the widget by
+    // default (note: it's not necessary to clear this in onDetach(), because
+    // the widget's onDetach will do so).
+    DOM.setEventListener(getElement(), this);
+
+    // Call onLoad() directly, because we're not calling super.onAttach().
+    onLoad();
+    AttachEvent.fire(this, true);
+  }
+
+  @Override
+  protected void onDetach() {
+    try {
+      onUnload();
+      AttachEvent.fire(this, false);
+    } finally {
+      // We don't want an exception in user code to keep us from calling the
+      // super implementation (or event listeners won't get cleaned up and
+      // the attached flag will be wrong).
+      getWidget().asWidget().onDetach();
+    }
+  }
+}
\ No newline at end of file
diff --git a/user/src/com/google/gwt/user/client/ui/Composite.java b/user/src/com/google/gwt/user/client/ui/Composite.java
index c90cc4e..3fdf5fa 100644
--- a/user/src/com/google/gwt/user/client/ui/Composite.java
+++ b/user/src/com/google/gwt/user/client/ui/Composite.java
@@ -15,115 +15,25 @@
  */
 package com.google.gwt.user.client.ui;
 
-import com.google.gwt.event.logical.shared.AttachEvent;
-import com.google.gwt.user.client.DOM;
-import com.google.gwt.user.client.Event;
-
 /**
- * A type of widget that can wrap another widget, hiding the wrapped widget's
- * methods. When added to a panel, a composite behaves exactly as if the widget
- * it wraps had been added.
- * 
- * <p>
- * The composite is useful for creating a single widget out of an aggregate of
- * multiple other widgets contained in a single panel.
- * </p>
- * 
- * <p>
+ * Simple extension of {@link AbstractComposite} that doesn't require type
+ * parameters. This originally was the only implementation of Composite, before
+ * {@link AbstractComposite} was introduced to allow strong typing and deferred
+ * construction.
+ *
  * <h3>Example</h3>
  * {@example com.google.gwt.examples.CompositeExample}
  * </p>
  */
-public abstract class Composite extends Widget {
-
-  private Widget widget;
-
-  @Override
-  public boolean isAttached() {
-    if (widget != null) {
-      return widget.isAttached();
-    }
-    return false;
-  }
-
-  @Override
-  public void onBrowserEvent(Event event) {
-    // Fire any handler added to the composite itself.
-    super.onBrowserEvent(event);
-
-    // Delegate events to the widget.
-    widget.onBrowserEvent(event);
-  }
-
+public abstract class Composite extends AbstractComposite<Widget> {
+  
   /**
-   * Provides subclasses access to the topmost widget that defines this
-   * composite.
-   * 
-   * @return the widget
+   * Provided for compatibility with legacy unit tests that mocked
+   * this specific method.
    */
-  protected Widget getWidget() {
-    return widget;
-  }
-
-  /**
-   * Sets the widget to be wrapped by the composite. The wrapped widget must be
-   * set before calling any {@link Widget} methods on this object, or adding it
-   * to a panel. This method may only be called once for a given composite.
-   * 
-   * @param widget the widget to be wrapped
-   */
-  protected void initWidget(Widget widget) {
-    // Validate. Make sure the widget is not being set twice.
-    if (this.widget != null) {
-      throw new IllegalStateException("Composite.initWidget() may only be "
-          + "called once.");
-    }
-
-    // Detach the new child.
-    widget.removeFromParent();
-
-    // Use the contained widget's element as the composite's element,
-    // effectively merging them within the DOM.
-    setElement(widget.getElement());
-
-    // Logical attach.
-    this.widget = widget;
-
-    // Adopt.
-    widget.setParent(this);
-  }
-
-  @Override
-  protected void onAttach() {
-    if (!isOrWasAttached()) {
-      widget.sinkEvents(eventsToSink);
-      eventsToSink = -1;
-    }
-
-    widget.onAttach();
-
-    // Clobber the widget's call to setEventListener(), causing all events to
-    // be routed to this composite, which will delegate back to the widget by
-    // default (note: it's not necessary to clear this in onDetach(), because
-    // the widget's onDetach will do so).
-    DOM.setEventListener(getElement(), this);
-
-    // Call onLoad() directly, because we're not calling super.onAttach().
-    onLoad();
-    AttachEvent.fire(this, true);
-  }
-
-  @Override
-  protected void onDetach() {
-    try {
-      onUnload();
-      AttachEvent.fire(this, false);
-    } finally {
-      // We don't want an exception in user code to keep us from calling the
-      // super implementation (or event listeners won't get cleaned up and
-      // the attached flag will be wrong).
-      widget.onDetach();
-    }
+  @Deprecated
+  protected void initWidget(Widget widget) { 
+    super.initWidget(widget);
   }
 
   /**
diff --git a/user/src/com/google/gwt/user/client/ui/RequiresResizeComposite.java b/user/src/com/google/gwt/user/client/ui/RequiresResizeComposite.java
new file mode 100644
index 0000000..d1a1003
--- /dev/null
+++ b/user/src/com/google/gwt/user/client/ui/RequiresResizeComposite.java
@@ -0,0 +1,31 @@
+/*
+ * Copyright 2011 Google Inc.
+ * 
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ * 
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.gwt.user.client.ui;
+
+/**
+ * A {@link AbstractComposite} implementation that implements {@link RequiresResize}
+ * and automatically delegates that interface's methods to its wrapped widget,
+ * which must itself implement {@link RequiresResize}.
+ * 
+ * @param <W> the type of widget wrapped
+ */
+public abstract class RequiresResizeComposite<W extends Widget & RequiresResize> extends
+    AbstractComposite<W> implements RequiresResize {
+
+  public void onResize() {
+    getWidget().onResize();
+  }
+}
diff --git a/user/src/com/google/gwt/user/client/ui/ResizeComposite.java b/user/src/com/google/gwt/user/client/ui/ResizeComposite.java
index 7d0bab3..1d2bc1d 100644
--- a/user/src/com/google/gwt/user/client/ui/ResizeComposite.java
+++ b/user/src/com/google/gwt/user/client/ui/ResizeComposite.java
@@ -19,7 +19,9 @@
  * A {@link Composite} implementation that implements {@link RequiresResize} and
  * automatically delegates that interface's methods to its wrapped widget, which
  * must itself implement {@link RequiresResize}.
+ * @deprecated Use {@link RequiresResizeComposite}
  */
+@Deprecated
 public abstract class ResizeComposite extends Composite implements
     RequiresResize {
 
diff --git a/user/src/com/google/gwt/user/client/ui/StackLayoutPanel.java b/user/src/com/google/gwt/user/client/ui/StackLayoutPanel.java
index e567de9..f5fe823 100644
--- a/user/src/com/google/gwt/user/client/ui/StackLayoutPanel.java
+++ b/user/src/com/google/gwt/user/client/ui/StackLayoutPanel.java
@@ -95,7 +95,7 @@
  * &lt;/g:StackLayoutPanel>
  * </pre>
  */
-public class StackLayoutPanel extends ResizeComposite implements HasWidgets,
+public class StackLayoutPanel extends RequiresResizeComposite<LayoutPanel> implements HasWidgets,
     ProvidesResize, IndexedPanel.ForIsWidget, AnimatedLayout,
     HasBeforeSelectionHandlers<Integer>, HasSelectionHandlers<Integer> {
 
diff --git a/user/src/com/google/gwt/user/client/ui/TabLayoutPanel.java b/user/src/com/google/gwt/user/client/ui/TabLayoutPanel.java
index 0c90414..365f8ee 100644
--- a/user/src/com/google/gwt/user/client/ui/TabLayoutPanel.java
+++ b/user/src/com/google/gwt/user/client/ui/TabLayoutPanel.java
@@ -94,7 +94,7 @@
  * &lt;/g:TabLayoutPanel>
  * </pre>
  */
-public class TabLayoutPanel extends ResizeComposite implements HasWidgets,
+public class TabLayoutPanel extends RequiresResizeComposite<LayoutPanel> implements HasWidgets,
     ProvidesResize, IndexedPanel.ForIsWidget, AnimatedLayout,
     HasBeforeSelectionHandlers<Integer>, HasSelectionHandlers<Integer> {