LUCENE-1754: just use EMPTY_DOCIDSET.iterator() instead of new EmptyDocIdSetIterator

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@798102 13f79535-47bb-0310-9956-ffa450edef68

contrib/miscellaneous/src/java/org/apache/lucene/misc/ChainedFilter.java

@@ -54,13 +54,12 @@ package org.apache.lucene.misc;
  * <http://www.apache.org/>.
  */
 
-import org.apache.lucene.index.IndexReader;
-import org.apache.lucene.search.Filter;
-
 import java.io.IOException;
+
+import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.search.DocIdSet;
 import org.apache.lucene.search.DocIdSetIterator;
-import org.apache.lucene.search.EmptyDocIdSetIterator;
+import org.apache.lucene.search.Filter;
 import org.apache.lucene.util.OpenBitSet;
 import org.apache.lucene.util.OpenBitSetDISI;
 import org.apache.lucene.util.SortedVIntList;
@@ -150,11 +149,11 @@ public class ChainedFilter extends Filter
     throws IOException {
         DocIdSet docIdSet = filter.getDocIdSet(reader);
         if (docIdSet == null) {
-          return EmptyDocIdSetIterator.getInstance();
+          return DocIdSet.EMPTY_DOCIDSET.iterator();
         } else {
           DocIdSetIterator iter = docIdSet.iterator();
           if (iter == null) {
-            return EmptyDocIdSetIterator.getInstance();
+            return DocIdSet.EMPTY_DOCIDSET.iterator();
           } else {
             return iter;
           }
@@ -275,11 +274,11 @@ public class ChainedFilter extends Filter
       } else {
         DocIdSetIterator disi;
         if (dis == null) {
-          disi = EmptyDocIdSetIterator.getInstance();
+          disi = DocIdSet.EMPTY_DOCIDSET.iterator();
         } else {
           disi = dis.iterator();
           if (disi == null) {
-            disi = EmptyDocIdSetIterator.getInstance();            
+            disi = DocIdSet.EMPTY_DOCIDSET.iterator();            
           }
         }
 

src/java/org/apache/lucene/search/ConstantScoreQuery.java

@@ -115,11 +115,11 @@ public class ConstantScoreQuery extends Query {
       theScore = w.getValue();
       DocIdSet docIdSet = filter.getDocIdSet(reader);
       if (docIdSet == null) {
-        docIdSetIterator = EmptyDocIdSetIterator.getInstance();
+        docIdSetIterator = DocIdSet.EMPTY_DOCIDSET.iterator();
       } else {
         DocIdSetIterator iter = docIdSet.iterator();
         if (iter == null) {
-          docIdSetIterator = EmptyDocIdSetIterator.getInstance();
+          docIdSetIterator = DocIdSet.EMPTY_DOCIDSET.iterator();
         } else {
           docIdSetIterator = iter;
         }

src/java/org/apache/lucene/search/DocIdSet.java

@@ -28,7 +28,18 @@ public abstract class DocIdSet {
 
   /** An empty {@code DocIdSet} instance for easy use (this is currently
    * implemented using a {@link SortedVIntList}). */
-  public static final DocIdSet EMPTY_DOCIDSET = new SortedVIntList(new int[0]);
+  public static final DocIdSet EMPTY_DOCIDSET = new SortedVIntList(new int[0]) {
+    
+    private final DocIdSetIterator iterator = new DocIdSetIterator() {
+      public int advance(int target) throws IOException { return NO_MORE_DOCS; }
+      public int docID() { return NO_MORE_DOCS; }
+      public int nextDoc() throws IOException { return NO_MORE_DOCS; }
+    };
+    
+    public DocIdSetIterator iterator() {
+      return iterator;
+    }
+  };
     
   /** Provides a {@link DocIdSetIterator} to access the set.
    * This may (but is not required to) return null if there

src/java/org/apache/lucene/search/EmptyDocIdSetIterator.java

@@ -1,42 +0,0 @@
-package org.apache.lucene.search;
-
-/**
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You 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.
- */
-
-import java.io.IOException;
-
-/**
- * An empty implementation for {@link DocIdSetIterator}. This can be used by
- * classes which receive a null {@link DocIdSet} from
- * {@link Filter#getDocIdSet(org.apache.lucene.index.IndexReader)}.
- */
-public final class EmptyDocIdSetIterator extends DocIdSetIterator {
-
-  private static final DocIdSetIterator instance = new EmptyDocIdSetIterator();
-  
-  public static DocIdSetIterator getInstance() { return instance; }
-  
-  // to prevent instantiation
-  private EmptyDocIdSetIterator() { }
-  
-  public int advance(int target) throws IOException { return NO_MORE_DOCS; }
-  
-  public int docID() { return NO_MORE_DOCS; }
-  
-  public int nextDoc() throws IOException { return NO_MORE_DOCS; }
-  
-}

src/java/org/apache/lucene/search/FilteredQuery.java

@@ -83,9 +83,9 @@ extends Query {
         }
         Filter f = FilteredQuery.this.filter;
         DocIdSet docIdSet = f.getDocIdSet(ir);
-        DocIdSetIterator docIdSetIterator = docIdSet == null ? EmptyDocIdSetIterator.getInstance() : docIdSet.iterator();
+        DocIdSetIterator docIdSetIterator = docIdSet == null ? DocIdSet.EMPTY_DOCIDSET.iterator() : docIdSet.iterator();
         if (docIdSetIterator == null) {
-          docIdSetIterator = EmptyDocIdSetIterator.getInstance();
+          docIdSetIterator = DocIdSet.EMPTY_DOCIDSET.iterator();
         }
         if (docIdSetIterator.advance(i) == i) {
           return inner;