/*********************************************************************************************************************** * Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu) * * 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 eu.stratosphere.pact.runtime.util; import java.io.IOException; import java.util.Iterator; import java.util.NoSuchElementException; import eu.stratosphere.api.common.typeutils.TypeSerializer; import eu.stratosphere.util.MutableObjectIterator; /** * This class wraps a {@link MutableObjectIterator} into a regular {@link Iterator}. * Internally, it uses two record instances which it uses alternating. That way, * whenever hasNext() returns (possibly with false), the previous obtained record is * still valid and cannot have been overwritten internally. */ public class MutableToRegularIteratorWrapper<T> implements Iterator<T> { private final MutableObjectIterator<T> source; private T current, next; private boolean currentIsAvailable; public MutableToRegularIteratorWrapper(MutableObjectIterator<T> source, TypeSerializer<T> serializer) { this.source = source; this.current = serializer.createInstance(); this.next = serializer.createInstance(); } @Override public boolean hasNext() { if (currentIsAvailable) { return true; } else { try { // we always use two records such that whenever hasNext() returns (possibly with false), // the previous record is always still valid. if ((next = source.next(next)) != null) { T tmp = current; current = next; next = tmp; currentIsAvailable = true; return true; } else { return false; } } catch (IOException ioex) { throw new RuntimeException("Error reading next record: " + ioex.getMessage(), ioex); } } } @Override public T next() { if (currentIsAvailable || hasNext()) { currentIsAvailable = false; return current; } else { throw new NoSuchElementException(); } } @Override public void remove() { throw new UnsupportedOperationException(); } }