diff options
3 files changed, 143 insertions, 0 deletions
diff --git a/src/main/java/com/amazon/carbonado/cursor/EmptyCursor.java b/src/main/java/com/amazon/carbonado/cursor/EmptyCursor.java index e0649cd..d851f0e 100644 --- a/src/main/java/com/amazon/carbonado/cursor/EmptyCursor.java +++ b/src/main/java/com/amazon/carbonado/cursor/EmptyCursor.java @@ -29,6 +29,7 @@ import com.amazon.carbonado.Cursor; * Special cursor implementation that is empty.
*
* @author Brian S O'Neill
+ * @see SingletonCursor
*/
public class EmptyCursor<S> implements Cursor<S> {
private static final Cursor EMPTY_CURSOR = new EmptyCursor();
diff --git a/src/main/java/com/amazon/carbonado/cursor/SingletonCursor.java b/src/main/java/com/amazon/carbonado/cursor/SingletonCursor.java new file mode 100644 index 0000000..55b6cb6 --- /dev/null +++ b/src/main/java/com/amazon/carbonado/cursor/SingletonCursor.java @@ -0,0 +1,103 @@ +/*
+ * Copyright 2006 Amazon Technologies, Inc. or its affiliates.
+ * Amazon, Amazon.com and Carbonado are trademarks or registered trademarks
+ * of Amazon Technologies, Inc. or its affiliates. All rights reserved.
+ *
+ * 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.amazon.carbonado.cursor;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+import com.amazon.carbonado.Cursor;
+
+/**
+ * Special cursor implementation that returns only one element.
+ *
+ * @author Brian S O'Neill
+ * @see EmptyCursor
+ */
+public class SingletonCursor<S> implements Cursor<S> {
+ private volatile S mObject;
+
+ /**
+ * @param object single object to return from cursor, must not be null
+ * @throws IllegalArgumentException if object is null
+ */
+ public SingletonCursor(S object) {
+ if (object == null) {
+ throw new IllegalArgumentException();
+ }
+ mObject = object;
+ }
+
+ public void close() {
+ mObject = null;
+ }
+
+ public boolean hasNext() {
+ return mObject != null;
+ }
+
+ public S next() {
+ S object = mObject;
+ mObject = null;
+ if (object == null) {
+ throw new NoSuchElementException();
+ }
+ return object;
+ }
+
+ public int skipNext(int amount) {
+ if (amount <= 0) {
+ if (amount < 0) {
+ throw new IllegalArgumentException("Cannot skip negative amount: " + amount);
+ }
+ return 0;
+ }
+ S object = mObject;
+ mObject = null;
+ return object == null ? 0 : 1;
+ }
+
+ public int copyInto(Collection<? super S> c) {
+ S object = mObject;
+ mObject = null;
+ if (object == null) {
+ return 0;
+ }
+ int originalSize = c.size();
+ c.add(object);
+ return originalSize + 1;
+ }
+
+ public int copyInto(Collection<? super S> c, int limit) {
+ return limit <= 0 ? 0 : copyInto(c);
+ }
+
+ public List<S> toList() {
+ List<S> list = new ArrayList<S>(1);
+ copyInto(list);
+ return list;
+ }
+
+ public List<S> toList(int limit) {
+ List<S> list = new ArrayList<S>(1);
+ copyInto(list, limit);
+ return list;
+ }
+}
diff --git a/src/test/java/com/amazon/carbonado/cursor/TestCursors.java b/src/test/java/com/amazon/carbonado/cursor/TestCursors.java index f063a59..fa5d8a7 100644 --- a/src/test/java/com/amazon/carbonado/cursor/TestCursors.java +++ b/src/test/java/com/amazon/carbonado/cursor/TestCursors.java @@ -20,6 +20,8 @@ package com.amazon.carbonado.cursor; import java.util.Arrays;
import java.util.Comparator;
+import java.util.List;
+import java.util.NoSuchElementException;
import junit.framework.TestCase;
import junit.framework.TestSuite;
@@ -53,6 +55,43 @@ public class TestCursors extends TestCase { protected void tearDown() {
}
+ public void testSingleton() throws Exception {
+ try {
+ new SingletonCursor<Object>(null);
+ fail();
+ } catch (IllegalArgumentException e) {
+ }
+
+ Cursor<String> cursor = new SingletonCursor<String>("hello");
+
+ assertTrue(cursor.hasNext());
+ assertEquals("hello", cursor.next());
+ assertFalse(cursor.hasNext());
+ try {
+ cursor.next();
+ fail();
+ } catch (NoSuchElementException e) {
+ }
+
+ assertEquals(0, cursor.skipNext(1));
+
+ cursor = new SingletonCursor<String>("world");
+ List<String> list = cursor.toList(0);
+ assertEquals(0, list.size());
+ list = cursor.toList(10);
+ assertEquals(1, list.size());
+ assertEquals("world", list.get(0));
+
+ cursor = new SingletonCursor<String>("world");
+ cursor.close();
+ assertFalse(cursor.hasNext());
+
+ cursor = new SingletonCursor<String>("world");
+ assertEquals(1, cursor.skipNext(2));
+ assertEquals(0, cursor.skipNext(1));
+ assertFalse(cursor.hasNext());
+ }
+
public void testUnion() throws Exception {
Cursor<Element> left, right, union;
|