Mega Code Archive
An Iterator that wraps a number of Iterators
<![CDATA[
/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* Copyright (c) 2008, Red Hat Middleware LLC or third-party contributors as
* indicated by the @author tags or express copyright attribution
* statements applied by the authors. All third-party contributions are
* distributed under license by Red Hat Middleware LLC.
*
* This copyrighted material is made available to anyone wishing to use, modify,
* copy, or redistribute it subject to the terms and conditions of the GNU
* Lesser General Public License, as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this distribution; if not, write to:
* Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA 02110-1301 USA
*
*/
import java.util.Iterator;
import java.util.List;
/**
* An JoinedIterator is an Iterator that wraps a number of Iterators.
*
* This class makes multiple iterators look like one to the caller.
* When any method from the Iterator interface is called, the JoinedIterator
* will delegate to a single underlying Iterator. The JoinedIterator will
* invoke the Iterators in sequence until all Iterators are exhausted.
*
*/
public class JoinedIterator implements Iterator {
private static final Iterator[] ITERATORS = {};
// wrapped iterators
private Iterator[] iterators;
// index of current iterator in the wrapped iterators array
private int currentIteratorIndex;
// the current iterator
private Iterator currentIterator;
// the last used iterator
private Iterator lastUsedIterator;
public JoinedIterator(List iterators) {
this( (Iterator[]) iterators.toArray(ITERATORS) );
}
public JoinedIterator(Iterator[] iterators) {
if( iterators==null )
throw new NullPointerException("Unexpected NULL iterators argument");
this.iterators = iterators;
}
public JoinedIterator(Iterator first, Iterator second) {
this( new Iterator[] { first, second } );
}
public boolean hasNext() {
updateCurrentIterator();
return currentIterator.hasNext();
}
public Object next() {
updateCurrentIterator();
return currentIterator.next();
}
public void remove() {
updateCurrentIterator();
lastUsedIterator.remove();
}
// call this before any Iterator method to make sure that the current Iterator
// is not exhausted
protected void updateCurrentIterator() {
if (currentIterator == null) {
if( iterators.length==0 ) {
currentIterator = EmptyIterator.emptyIterator;
}
else {
currentIterator = iterators[0];
}
// set last used iterator here, in case the user calls remove
// before calling hasNext() or next() (although they shouldn't)
lastUsedIterator = currentIterator;
}
while (! currentIterator.hasNext() && currentIteratorIndex < iterators.length - 1) {
currentIteratorIndex++;
currentIterator = iterators[currentIteratorIndex];
}
}
}
/* Copyright 2004 BEA Systems, Inc.
*
* 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.
*/
class EmptyIterator implements java.util.Iterator {
public static final EmptyIterator emptyIterator = new EmptyIterator();
public boolean hasNext() { return false; }
public Object next() { return null; }
public void remove() {
throw new UnsupportedOperationException();
}
}
]]>