Make DragSourceExtension and DragTargetExtension generic (#8628)

* Make DragSourceExtension and DropTargetExtension generic (#8440)

* Apply generalization of drag and drop extensions in #8440

* Override javadocs to be more specific

8 files changed, 150 insertions, 75 deletions

diff --git a/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java b/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java
index 6f094ce9e2..47abea4eae 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragEndEvent.java
@@ -23,28 +23,31 @@ import com.vaadin.shared.ui.dnd.EffectAllowed;
 import com.vaadin.ui.Component;
 
 /**
- * Server side dragend event. Fired when an HTML5 dragend happens.
+ * Server side dragend event. Fired when an HTML5 dragend happens on the client.
  *
+ * @param <T>
+ *         Type of the component that was dragged.
  * @see DragSourceExtension#addDragEndListener(DragEndListener)
  */
-public class DragEndEvent extends Component.Event {
+public class DragEndEvent<T extends Component> extends Component.Event {
     private final Map<String, String> data;
     private final EffectAllowed effectAllowed;
 
     /**
-     * Creates a new server side dragend event.
+     * Creates a server side dragend event.
      *
      * @param source
-     *         Draggable component.
+     *         Component that was dragged.
      * @param types
-     *         List of data types from {@code DataTransfer.types}.
+     *         List of data types from {@code DataTransfer.types} object.
      * @param data
-     *         Map of all data from {@code DataTransfer}.
+     *         Map containing all types and corresponding data from the {@code
+     *         DataTransfer} object.
      * @param effectAllowed
-     *         Parameter from {@code DataTransfer.effectAllowed}.
+     *         Allowed effects from {@code DataTransfer.effectAllowed} object.
      */
-    public DragEndEvent(Component source, List<String> types,
-            Map<String, String> data, EffectAllowed effectAllowed) {
+    public DragEndEvent(T source, List<String> types, Map<String, String> data,
+            EffectAllowed effectAllowed) {
         super(source);
 
         // Create a linked map that preserves the order of types
@@ -74,4 +77,15 @@ public class DragEndEvent extends Component.Event {
     public EffectAllowed getEffectAllowed() {
         return effectAllowed;
     }
+
+    /**
+     * Returns the drag source component where the dragend event occurred.
+     *
+     * @return Component which was dragged.
+     */
+    @Override
+    @SuppressWarnings("unchecked")
+    public T getComponent() {
+        return (T) super.getComponent();
+    }
 }
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragEndListener.java b/server/src/main/java/com/vaadin/event/dnd/DragEndListener.java
index 00a020353d..7b35bcab1d 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragEndListener.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragEndListener.java
@@ -18,23 +18,27 @@ package com.vaadin.event.dnd;
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
+import com.vaadin.ui.Component;
 
 /**
  * Interface to be implemented when creating a dragend listener on a drag
  * source for HTML5 drag and drop.
  *
+ * @param <T>
+ *         Type of draggable component.
  * @see DragSourceExtension#addDragEndListener(DragEndListener)
  */
 @FunctionalInterface
-public interface DragEndListener extends ConnectorEventListener {
+public interface DragEndListener<T extends Component> extends
+        ConnectorEventListener {
     static final Method DRAGEND_METHOD = DragEndListener.class
             .getDeclaredMethods()[0];
 
     /**
-     * Called when a server side dragend event is fired.
+     * Called when dragend event is fired.
      *
      * @param event
-     *         The dragend event that is fired.
+     *         Server side dragend event.
      */
-    void dragEnd(DragEndEvent event);
+    void dragEnd(DragEndEvent<T> event);
 }
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragSourceExtension.java b/server/src/main/java/com/vaadin/event/dnd/DragSourceExtension.java
index d90e1bd8b8..78f606c05a 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragSourceExtension.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragSourceExtension.java
@@ -20,7 +20,6 @@ import java.util.LinkedHashMap;
 import java.util.Map;
 import java.util.Objects;
 
-import com.vaadin.server.AbstractClientConnector;
 import com.vaadin.server.AbstractExtension;
 import com.vaadin.shared.Registration;
 import com.vaadin.shared.ui.dnd.DragSourceRpc;
@@ -29,41 +28,40 @@ import com.vaadin.shared.ui.dnd.EffectAllowed;
 import com.vaadin.ui.AbstractComponent;
 
 /**
- * Extension to add drag source functionality to a component for using HTML5
- * drag and drop.
+ * Extension to make a component drag source for HTML5 drag and drop
+ * functionality.
+ *
+ * @param <T>
+ *         Type of the component to be extended.
  */
-public class DragSourceExtension extends AbstractExtension {
+public class DragSourceExtension<T extends AbstractComponent> extends
+        AbstractExtension {
 
     /**
-     * Constructor for {@link DragSourceExtension}
+     * Extends {@code target} component and makes it a drag source.
+     *
+     * @param target
+     *         Component to be extended.
      */
-    public DragSourceExtension() {
+    public DragSourceExtension(T target) {
         registerRpc(new DragSourceRpc() {
             @Override
             public void dragStart() {
-                DragStartEvent event = new DragStartEvent(
-                        (AbstractComponent) getParent(), getState(false).types,
-                        getState(false).data, getState(false).effectAllowed);
+                DragStartEvent<T> event = new DragStartEvent<>(target,
+                        getState(false).types, getState(false).data,
+                        getState(false).effectAllowed);
                 fireEvent(event);
             }
 
             @Override
             public void dragEnd() {
-                DragEndEvent event = new DragEndEvent(
-                        (AbstractComponent) getParent(), getState(false).types,
-                        getState(false).data, getState(false).effectAllowed);
+                DragEndEvent<T> event = new DragEndEvent<>(target,
+                        getState(false).types, getState(false).data,
+                        getState(false).effectAllowed);
                 fireEvent(event);
             }
         });
-    }
 
-    /**
-     * Makes {@code target} component a drag source.
-     *
-     * @param target
-     *         Component to be extended.
-     */
-    public void extend(AbstractComponent target) {
         super.extend(target);
     }
 
@@ -194,7 +192,7 @@ public class DragSourceExtension extends AbstractExtension {
      *         Listener to handle dragstart event.
      * @return Handle to be used to remove this listener.
      */
-    public Registration addDragStartListener(DragStartListener listener) {
+    public Registration addDragStartListener(DragStartListener<T> listener) {
         return addListener(DragSourceState.EVENT_DRAGSTART,
                 DragStartEvent.class, listener,
                 DragStartListener.DRAGSTART_METHOD);
@@ -209,7 +207,7 @@ public class DragSourceExtension extends AbstractExtension {
      *         Listener to handle dragend event.
      * @return Handle to be used to remove this listener.
      */
-    public Registration addDragEndListener(DragEndListener listener) {
+    public Registration addDragEndListener(DragEndListener<T> listener) {
         return addListener(DragSourceState.EVENT_DRAGEND, DragEndEvent.class,
                 listener, DragEndListener.DRAGEND_METHOD);
     }
@@ -223,4 +221,15 @@ public class DragSourceExtension extends AbstractExtension {
     protected DragSourceState getState(boolean markAsDirty) {
         return (DragSourceState) super.getState(markAsDirty);
     }
+
+    /**
+     * Returns the component this extension is attached to.
+     *
+     * @return Extended component.
+     */
+    @Override
+    @SuppressWarnings("unchecked")
+    public T getParent() {
+        return (T) super.getParent();
+    }
 }
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java b/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java
index 591a0e61a7..de6a1a79f4 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragStartEvent.java
@@ -23,27 +23,31 @@ import com.vaadin.shared.ui.dnd.EffectAllowed;
 import com.vaadin.ui.Component;
 
 /**
- * Server side dragstart event. Fired when an HTML5 dragstart happens.
+ * Server side dragstart event. Fired when an HTML5 dragstart happens on the
+ * client.
  *
+ * @param <T>
+ *         Type of the component that is dragged.
  * @see DragSourceExtension#addDragStartListener(DragStartListener)
  */
-public class DragStartEvent extends Component.Event {
+public class DragStartEvent<T extends Component> extends Component.Event {
     private final Map<String, String> data;
     private final EffectAllowed effectAllowed;
 
     /**
-     * Creates a new server side dragend event.
+     * Creates a server side dragstart event.
      *
      * @param source
-     *         Draggable component.
+     *         Component that is dragged.
      * @param types
-     *         List of data types from {@code DataTransfer.types}.
+     *         List of data types from {@code DataTransfer.types} object.
      * @param data
-     *         Map of all data from {@code DataTransfer}.
+     *         Map containing all types and corresponding data from the {@code
+     *         DataTransfer} object.
      * @param effectAllowed
-     *         Parameter from {@code DataTransfer.effectAllowed}.
+     *         Allowed effects from {@code DataTransfer.effectAllowed} object.
      */
-    public DragStartEvent(Component source, List<String> types,
+    public DragStartEvent(T source, List<String> types,
             Map<String, String> data, EffectAllowed effectAllowed) {
         super(source);
 
@@ -74,4 +78,15 @@ public class DragStartEvent extends Component.Event {
     public EffectAllowed getEffectAllowed() {
         return effectAllowed;
     }
+
+    /**
+     * Returns the drag source component where the dragstart event occurred.
+     *
+     * @return Component which is dragged.
+     */
+    @Override
+    @SuppressWarnings("unchecked")
+    public T getComponent() {
+        return (T) super.getComponent();
+    }
 }
diff --git a/server/src/main/java/com/vaadin/event/dnd/DragStartListener.java b/server/src/main/java/com/vaadin/event/dnd/DragStartListener.java
index 8d691dee6b..a9536144d9 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DragStartListener.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DragStartListener.java
@@ -18,23 +18,27 @@ package com.vaadin.event.dnd;
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
+import com.vaadin.ui.Component;
 
 /**
  * Interface to be implemented when creating a dragstart listener on a drag
  * source for HTML5 drag and drop.
  *
+ * @param <T>
+ *         Type of draggable component.
  * @see DragSourceExtension#addDragStartListener(DragStartListener)
  */
 @FunctionalInterface
-public interface DragStartListener extends ConnectorEventListener {
+public interface DragStartListener<T extends Component> extends
+        ConnectorEventListener {
     static final Method DRAGSTART_METHOD = DragStartListener.class
             .getDeclaredMethods()[0];
 
     /**
-     * Called when a server side dragstart event is fired.
+     * Called when dragstart event is fired.
      *
      * @param event
-     *         The dragstart event that is fired.
+     *         Server side dragstart event.
      */
-    void dragStart(DragStartEvent event);
+    void dragStart(DragStartEvent<T> event);
 }
diff --git a/server/src/main/java/com/vaadin/event/dnd/DropEvent.java b/server/src/main/java/com/vaadin/event/dnd/DropEvent.java
index 382b93bc55..5257a06367 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropEvent.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DropEvent.java
@@ -25,26 +25,29 @@ import com.vaadin.ui.Component;
 /**
  * Server side drop event. Fired when an HTML5 drop happens.
  *
+ * @param <T>
+ *         Type of the drop target component.
  * @see DropTargetExtension#addDropListener(DropListener)
  */
-public class DropEvent extends Component.Event {
+public class DropEvent<T extends Component> extends Component.Event {
     private final Map<String, String> data;
     private final DropEffect dropEffect;
 
     /**
-     * Creates a new server side drop event.
+     * Creates a server side drop event.
      *
      * @param source
-     *         Drop target component.
+     *         Component that is dragged.
      * @param types
-     *         List of data types from {@code DataTransfer.types}.
+     *         List of data types from {@code DataTransfer.types} object.
      * @param data
-     *         Map of all data from {@code DataTransfer}.
+     *         Map containing all types and corresponding data from the {@code
+     *         DataTransfer} object.
      * @param dropEffect
-     *         Parameter from {@code DataTransfer.dropEffect}.
+     *         Drop effect from {@code DataTransfer.dropEffect} object.
      */
-    public DropEvent(Component source, List<String> types,
-            Map<String, String> data, DropEffect dropEffect) {
+    public DropEvent(T source, List<String> types, Map<String, String> data,
+            DropEffect dropEffect) {
         super(source);
 
         // Create a linked map that preserves the order of types
@@ -74,4 +77,15 @@ public class DropEvent extends Component.Event {
     public DropEffect getDropEffect() {
         return dropEffect;
     }
+
+    /**
+     * Returns the drop target component where the drop event occurred.
+     *
+     * @return Component on which a drag source was dropped.
+     */
+    @Override
+    @SuppressWarnings("unchecked")
+    public T getComponent() {
+        return (T) super.getComponent();
+    }
 }
diff --git a/server/src/main/java/com/vaadin/event/dnd/DropListener.java b/server/src/main/java/com/vaadin/event/dnd/DropListener.java
index 8cb96d1852..41c1bfc6ff 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropListener.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DropListener.java
@@ -18,21 +18,27 @@ package com.vaadin.event.dnd;
 import java.lang.reflect.Method;
 
 import com.vaadin.event.ConnectorEventListener;
+import com.vaadin.ui.Component;
 
 /**
  * Interface to be implemented when creating a drop listener on a drop target
- * for HTML5 drag and drop. See {@link DropTargetExtension#addDropListener(DropListener)}.
+ * for HTML5 drag and drop.
+ *
+ * @param <T>
+ *         Type of the drop target component.
+ * @see DropTargetExtension#addDropListener(DropListener)
  */
 @FunctionalInterface
-public interface DropListener extends ConnectorEventListener {
+public interface DropListener<T extends Component> extends
+        ConnectorEventListener {
     static final Method DROP_METHOD = DropListener.class
             .getDeclaredMethods()[0];
 
     /**
-     * Called when a server side drop event is fired.
+     * Called when drop event is fired.
      *
      * @param event
-     *         The drop event that is fired.
+     *         Server side drop event.
      */
-    void drop(DropEvent event);
+    void drop(DropEvent<T> event);
 }
diff --git a/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java b/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java
index 20819ec70f..4fdd606eb5 100644
--- a/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java
+++ b/server/src/main/java/com/vaadin/event/dnd/DropTargetExtension.java
@@ -17,7 +17,6 @@ package com.vaadin.event.dnd;
 
 import java.util.Objects;
 
-import com.vaadin.server.AbstractClientConnector;
 import com.vaadin.server.AbstractExtension;
 import com.vaadin.shared.Registration;
 import com.vaadin.shared.ui.dnd.DropEffect;
@@ -28,28 +27,27 @@ import com.vaadin.ui.AbstractComponent;
 /**
  * Extension to add drop target functionality to a widget for using HTML5 drag
  * and drop.
+ *
+ * @param <T>
+ *         Type of the component to be extended.
  */
-public class DropTargetExtension extends AbstractExtension {
+public class DropTargetExtension<T extends AbstractComponent> extends
+        AbstractExtension {
 
     /**
-     * Constructor for {@link DropTargetExtension}.
+     * Extends {@code target} component and makes it a drop target.
+     *
+     * @param target
+     *         Component to be extended.
      */
-    public DropTargetExtension() {
+    public DropTargetExtension(T target) {
         registerRpc((DropTargetRpc) (types, data, dropEffect) -> {
-            DropEvent event = new DropEvent((AbstractComponent) getParent(),
-                    types, data, dropEffect);
+            DropEvent<T> event = new DropEvent<>(target, types, data,
+                    dropEffect);
 
             fireEvent(event);
         });
-    }
 
-    /**
-     * Makes {@code target} component a drop target.
-     *
-     * @param target
-     *         Component to be extended.
-     */
-    public void extend(AbstractComponent target) {
         super.extend(target);
     }
 
@@ -129,7 +127,7 @@ public class DropTargetExtension extends AbstractExtension {
      *         Listener to handle drop event.
      * @return Handle to be used to remove this listener.
      */
-    public Registration addDropListener(DropListener listener) {
+    public Registration addDropListener(DropListener<T> listener) {
         return addListener(DropEvent.class, listener, DropListener.DROP_METHOD);
     }
 
@@ -142,4 +140,15 @@ public class DropTargetExtension extends AbstractExtension {
     protected DropTargetState getState(boolean markAsDirty) {
         return (DropTargetState) super.getState(markAsDirty);
     }
+
+    /**
+     * Returns the component this extension is attached to.
+     *
+     * @return Extended component.
+     */
+    @Override
+    @SuppressWarnings("unchecked")
+    public T getParent() {
+        return (T) super.getParent();
+    }
 }