Added SingletonCursor.

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;