1 files changed, 110 insertions, 0 deletions
diff --git a/src/main/java/com/amazon/carbonado/cursor/ViewCursor.java b/src/main/java/com/amazon/carbonado/cursor/ViewCursor.java
new file mode 100644
index 0000000..01b02c3
--- /dev/null
+++ b/src/main/java/com/amazon/carbonado/cursor/ViewCursor.java
@@ -0,0 +1,110 @@
+/*
+ * Copyright 2007 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.NoSuchElementException;
+
+import com.amazon.carbonado.Cursor;
+import com.amazon.carbonado.FetchException;
+
+/**
+ * Wraps another cursor and only produces a range of elements. The range might
+ * be smaller if the source cursor doesn't have enough elements.
+ *
+ * @author Brian S O'Neill
+ * @since 1.2
+ */
+public class ViewCursor<S> extends AbstractCursor<S> {
+    private final Cursor<S> mSource;
+
+    private volatile long mFrom;
+    private volatile long mRemaining;
+
+    /**
+     * @param from zero-based element to start from, inclusive
+     * @param to zero-based element to end at, exclusive
+     * @throws IllegalArgumentException if source is null, from is negative or
+     * if from is more than to
+     */
+    public ViewCursor(Cursor<S> source, long from, long to) {
+        if (source == null) {
+            throw new IllegalArgumentException("Source is null");
+        }
+        if (from < 0) {
+            throw new IllegalArgumentException("From is negative: " + from);
+        }
+        mSource = source;
+        mFrom = from;
+        mRemaining = to - from;
+        if (mRemaining <= 0) {
+            if (mRemaining < 0) {
+                throw new IllegalArgumentException("From is more than to: " + from + " > " + to);
+            }
+            // Don't bother skipping.
+            mFrom = 0;
+        }
+    }
+
+    public void close() throws FetchException {
+        mSource.close();
+    }
+
+    public boolean hasNext() throws FetchException {
+        if (mFrom > 0) {
+            while (mFrom > Integer.MAX_VALUE) {
+                mFrom -= mSource.skipNext(Integer.MAX_VALUE);
+            }
+            mSource.skipNext((int) mFrom);
+            mFrom = 0;
+        }
+        if (mSource.hasNext()) {
+            if (mRemaining > 0) {
+                return true;
+            }
+            mSource.close();
+        }
+        return false;
+    }
+
+    public S next() throws FetchException {
+        if (!hasNext()) {
+            throw new NoSuchElementException();
+        }
+        S next = mSource.next();
+        if (--mRemaining <= 0) {
+            mSource.close();
+        }
+        return next;
+    }
+
+    @Override
+    public int skipNext(int amount) throws FetchException {
+        if (!hasNext()) {
+            return 0;
+        }
+        if (amount > mRemaining) {
+            amount = (int) mRemaining;
+        }
+        amount = mSource.skipNext(amount);
+        if ((mRemaining -= amount) <= 0) {
+            mSource.close();
+        }
+        return amount;
+    }
+}