Add empty default methods to LookupListener interface

platform/lang-api/src/com/intellij/codeInsight/lookup/LookupListener.java

-/*
- * Copyright 2000-2009 JetBrains s.r.o.
- *
- * 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.
- */
+// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 
 package com.intellij.codeInsight.lookup;
 
 import java.util.EventListener;
 
+/**
+ * Listener to receive notifications for events in lookup.
+ *
+ * @see Lookup#addLookupListener(LookupListener)
+ */
 public interface LookupListener extends EventListener {
   /*
    * Note: this event comes inside the command that performs inserting of text into the editor.
    */
-  void itemSelected(LookupEvent event);
+  default void itemSelected(LookupEvent event) {
+  }
 
-  void lookupCanceled(LookupEvent event);
+  default void lookupCanceled(LookupEvent event) {
+  }
 
-  void currentItemChanged(LookupEvent event);
-}
\ No newline at end of file
+  default void currentItemChanged(LookupEvent event) {
+  }
+}

platform/lang-impl/src/com/intellij/codeInsight/lookup/LookupAdapter.java

-/*
- * Copyright 2000-2009 JetBrains s.r.o.
- *
- * 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.
- */
+// Copyright 2000-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
 
 package com.intellij.codeInsight.lookup;
 
+/**
+ * @deprecated Use LookupListener directly
+ */
 public abstract class LookupAdapter implements LookupListener{
   @Override
   public void itemSelected(LookupEvent event){