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/*******************************************************************************
* Copyright (c) 2005, 2009 Oracle. All rights reserved.
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v1.0, which accompanies this distribution
* and is available at http://www.eclipse.org/legal/epl-v10.html.
*
* Contributors:
* Oracle - initial API and implementation
******************************************************************************/
package org.eclipse.jpt.utility.internal.iterators;
import java.util.Iterator;
import java.util.NoSuchElementException;
import org.eclipse.jpt.utility.internal.StringTools;
import org.eclipse.jpt.utility.internal.iterables.ArrayIterable;
/**
* A <code>CompositeIterator</code> wraps a collection
* of {@link Iterator}s and makes them appear to be a single
* {@link Iterator}.
*
* @param <E> the type of elements returned by the iterator
*
* @see org.eclipse.jpt.utility.internal.iterables.CompositeIterable
*/
public class CompositeIterator<E>
implements Iterator<E>
{
private final Iterator<? extends Iterator<? extends E>> iterators;
private Iterator<? extends E> currentIterator;
private Iterator<? extends E> lastIteratorToReturnNext;
// ********** constructors **********
/**
* Construct an iterator that returns all the elements held by the
* specified iterables.
*/
public CompositeIterator(Iterable<? extends Iterable<? extends E>> iterables) {
this(
new TransformationIterator<Iterable<? extends E>, Iterator<? extends E>>(iterables.iterator()) {
@Override
protected Iterator<? extends E> transform(Iterable<? extends E> iterable) {
return iterable.iterator();
}
}
);
}
/**
* Construct an iterator with the specified collection of iterators.
*/
public CompositeIterator(Iterator<? extends Iterator<? extends E>> iterators) {
super();
this.iterators = iterators;
}
/**
* Construct an iterator with the specified object prepended
* to the specified iterable.
*/
public CompositeIterator(E object, Iterable<? extends E> iterable) {
this(object, iterable.iterator());
}
/**
* Construct an iterator with the specified object prepended
* to the specified iterator.
*/
@SuppressWarnings("unchecked")
public CompositeIterator(E object, Iterator<? extends E> iterator) {
this(new SingleElementIterator<E>(object), iterator);
}
/**
* Construct an iterator with the specified object appended
* to the specified iterable.
*/
public CompositeIterator(Iterable<? extends E> iterable, E object) {
this(iterable.iterator(), object);
}
/**
* Construct an iterator with the specified object appended
* to the specified iterator.
*/
@SuppressWarnings("unchecked")
public CompositeIterator(Iterator<? extends E> iterator, E object) {
this(iterator, new SingleElementIterator<E>(object));
}
/**
* Construct an iterator with the specified iterables.
*/
public CompositeIterator(Iterable<? extends E>... iterables) {
this(new ArrayIterable<Iterable<? extends E>>(iterables));
}
/**
* Construct an iterator with the specified iterators.
*/
public CompositeIterator(Iterator<? extends E>... iterators) {
this(new ArrayIterator<Iterator<? extends E>>(iterators));
}
// ********** Iterator implementation **********
public boolean hasNext() {
try {
this.loadCurrentIterator();
} catch (NoSuchElementException ex) {
// this occurs if there are no iterators at all
return false;
}
return this.currentIterator.hasNext();
}
public E next() {
this.loadCurrentIterator();
E result = this.currentIterator.next();
// the statement above will throw a NoSuchElementException
// if the current iterator is at the end of the line;
// so if we get here, we can set 'lastIteratorToReturnNext'
this.lastIteratorToReturnNext = this.currentIterator;
return result;
}
public void remove() {
if (this.lastIteratorToReturnNext == null) {
// CompositeIterator#next() has never been called
throw new IllegalStateException();
}
this.lastIteratorToReturnNext.remove();
}
/**
* Load {@link currentIterator} with the first iterator that {@link Iterator#hasNext()}
* or the final iterator if all the elements have already been retrieved.
*/
private void loadCurrentIterator() {
if (this.currentIterator == null) {
this.currentIterator = this.iterators.next();
}
while (( ! this.currentIterator.hasNext()) && this.iterators.hasNext()) {
this.currentIterator = this.iterators.next();
}
}
// ********** overrides **********
@Override
public String toString() {
return StringTools.buildToStringFor(this, this.iterators);
}
}
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