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/*******************************************************************************
* Copyright (c) 2009, 2017 Cloudsmith Inc. and others.
* 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:
* Cloudsmith Inc. - initial API and implementation
*******************************************************************************/
package org.eclipse.equinox.internal.p2.metadata.expression;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* A CompoundIterator will assume that its contained iterator that will produce
* elements that in turn can be represented as iterators. The elements of those
* iterators will be returned in sequence, thus removing one iterator dimension.
* Elements of the contained iterator that are not iterators will be coerced
* into iterators using {@link RepeatableIterator#create(Object)}.
*/
public class CompoundIterator<T> implements Iterator<T> {
private static final Object NO_ELEMENT = new Object();
private final Iterator<? extends Object> iteratorIterator;
private Iterator<T> currentIterator;
private T nextObject = noElement();
/**
* Creates a compound iterator that will iterated over the elements
* of the provided <code>iterator</code>. Each element will be coerced
* into an iterator and its elements in turn are returned
* in succession by the compound iterator.
*
* @param iterator
*/
public CompoundIterator(Iterator<? extends Object> iterator) {
this.iteratorIterator = iterator;
}
@Override
public boolean hasNext() {
return positionNext();
}
@Override
public T next() {
if (!positionNext())
throw new NoSuchElementException();
T nxt = nextObject;
nextObject = noElement();
return nxt;
}
/**
* Remove is not supported by this iterator so calling this method
* will always yield an exception.
* @throws UnsupportedOperationException
*/
@Override
public void remove() {
throw new UnsupportedOperationException();
}
@SuppressWarnings("unchecked")
private boolean positionNext() {
if (nextObject != NO_ELEMENT)
return true;
while (currentIterator == null || !currentIterator.hasNext()) {
if (!iteratorIterator.hasNext())
return false;
Object nextItor = iteratorIterator.next();
currentIterator = (nextItor instanceof Iterator<?>) ? (Iterator<T>) nextItor : RepeatableIterator.<T> create(nextItor);
}
nextObject = currentIterator.next();
return true;
}
@SuppressWarnings("unchecked")
private static <T> T noElement() {
return (T) NO_ELEMENT;
}
}
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