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/*
* Copyright 2006-2012 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.Comparator;
import java.util.NoSuchElementException;
import com.amazon.carbonado.FetchException;
import com.amazon.carbonado.Cursor;
/**
* Wraps two Cursors and performs a <i>symmetric set difference</i>
* operation. In boolean logic, this is an <i>exclusive or</i> operation.
*
* <p>Both cursors must return results in the same order. Ordering is preserved
* by the difference.
*
* @author Brian S O'Neill
* @see UnionCursor
* @see IntersectionCursor
* @see DifferenceCursor
*/
public class SymmetricDifferenceCursor<S> extends AbstractCursor<S> {
private final Cursor<S> mLeftCursor;
private final Cursor<S> mRightCursor;
private final Comparator<S> mOrder;
private S mNextLeft;
private S mNextRight;
private int mCompareResult;
/**
* @param left cursor to wrap
* @param right cursor to wrap
* @param order describes sort ordering of wrapped cursors, which must be
* a total ordering
*/
public SymmetricDifferenceCursor(Cursor<S> left, Cursor<S> right, Comparator<S> order) {
if (left == null || right == null || order == null) {
throw new IllegalArgumentException();
}
mLeftCursor = left;
mRightCursor = right;
mOrder = order;
}
public void close() throws FetchException {
mLeftCursor.close();
mRightCursor.close();
mNextLeft = null;
mNextRight = null;
}
public boolean hasNext() throws FetchException {
try {
return compareNext() != 0;
} catch (FetchException e) {
try {
close();
} catch (Exception e2) {
// Don't care.
}
throw e;
}
}
/**
* Returns 0 if no next element available, {@literal <0} if next element is
* from left source cursor, and {@literal >0} if next element is from right
* source cursor.
*/
public int compareNext() throws FetchException {
if (mCompareResult != 0) {
return mCompareResult;
}
try {
while (true) {
if (mNextLeft == null && mLeftCursor.hasNext()) {
mNextLeft = mLeftCursor.next();
}
if (mNextRight == null && mRightCursor.hasNext()) {
mNextRight = mRightCursor.next();
}
if (mNextLeft == null) {
return mNextRight != null ? 1 : 0;
}
if (mNextRight == null) {
return -1;
}
if ((mCompareResult = mOrder.compare(mNextLeft, mNextRight)) == 0) {
mNextLeft = null;
mNextRight = null;
} else {
return mCompareResult;
}
}
} catch (NoSuchElementException e) {
return 0;
} catch (FetchException e) {
try {
close();
} catch (Exception e2) {
// Don't care.
}
throw e;
}
}
public S next() throws FetchException {
try {
S next;
int result = compareNext();
if (result < 0) {
next = mNextLeft;
mNextLeft = null;
} else if (result > 0) {
next = mNextRight;
mNextRight = null;
} else {
throw new NoSuchElementException();
}
mCompareResult = 0;
return next;
} catch (FetchException e) {
try {
close();
} catch (Exception e2) {
// Don't care.
}
throw e;
}
}
}
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