/*
* This file is part of the X10 project (http://x10-lang.org).
*
* This file is licensed to You under the Eclipse Public License (EPL);
* You may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.opensource.org/licenses/eclipse-1.0.php
*
* This file was originally derived from the Polyglot extensible compiler framework.
*
* (C) Copyright 2000-2007 Polyglot project group, Cornell University
* (C) Copyright IBM Corporation 2007-2012.
*/
package polyglot.util;
import java.util.Iterator;
import java.util.Collection;
/**
* TransformingIterator
*
* Overview:
* This is a swiss-army-knife of iterators. It concatenates, maps, and
* filters.
*
* Does not support Remove.
**/
public final class TransformingIterator<S,T> implements Iterator<T> {
@SuppressWarnings("unchecked") // Generics and arrays don't mix well
public TransformingIterator(Iterator<S> iter, Transformation<S,T> trans) {
this(new Iterator[]{iter}, trans);
}
@SuppressWarnings("unchecked") // Generics and arrays don't mix well
public TransformingIterator(Collection<S> iters, Transformation<S,T> trans) {
index = 0;
backing_iterators = (Iterator<S>[]) iters.toArray(new Iterator[0]);
transformation = trans;
if (backing_iterators.length > 0)
current_iter = backing_iterators[0];
findNextItem();
}
public TransformingIterator(Iterator<S>[] iters, Transformation<S,T> trans) {
index = 0;
backing_iterators = (Iterator<S>[]) iters.clone();
transformation = trans;
if (iters.length > 0)
current_iter = iters[0];
findNextItem();
}
public T next() {
T res = next_item;
if (res == null)
throw new java.util.NoSuchElementException();
findNextItem();
return res;
}
public boolean hasNext() {
return next_item != null;
}
public void remove() {
throw new UnsupportedOperationException("TransformingIterator.remove");
}
// Advances the internal iterator.
private void findNextItem() {
while (current_iter != null) {
inner_loop:
while (current_iter.hasNext()) {
S o = current_iter.next();
T res = transformation.transform(o);
if (res == null)
continue inner_loop;
next_item = res;
return;
}
index++;
if (index < backing_iterators.length) {
current_iter = (Iterator<S>) backing_iterators[index];
} else {
current_iter = null;
}
}
next_item = null;
}
// AF: if next_item==null, this iterator has no more elts to yield.
// otherwise, this iterator will yield next_item, followed by
// those elements e of backing_iterator[index] transformed by TRANS.
// RI: current_iter = backing_iterators[index], or null if no
// backing_iterator hasNext.
protected T next_item;
protected Iterator<S> current_iter;
protected int index;
protected Iterator<S>[] backing_iterators;
protected Transformation<S,T> transformation;
}