From 10d42c88a173ad79d629e91b7481d6d62922070c Mon Sep 17 00:00:00 2001
From: "Brian S. O'Neill" <bronee@gmail.com>
Date: Mon, 21 May 2007 00:12:37 +0000
Subject: Added ViewCursor class.
---
.../com/amazon/carbonado/cursor/ViewCursor.java | 110 +++++++++++++++++++++
1 file changed, 110 insertions(+)
create mode 100644 src/main/java/com/amazon/carbonado/cursor/ViewCursor.java
(limited to 'src/main/java/com/amazon/carbonado/cursor')
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;
+ }
+}
--
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