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A lightweight alternative to Java 8 sequential Stream
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/*
* Copyright 2016 Daniel Skogquist Åborg
*
* 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 org.d2ab.iterator;
import org.d2ab.util.Pair;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.function.Function;
public class LeftFlatteningPairIterator extends DelegatingMappingIterator, Pair> {
private final Function super Pair, ? extends Iterable> mapper;
private Iterator leftIterator = Iterators.empty();
private Pair pair;
public LeftFlatteningPairIterator(Iterator> iterator,
Function super Pair, ? extends Iterable> mapper) {
super(iterator);
this.mapper = mapper;
}
@Override
public boolean hasNext() {
while (!leftIterator.hasNext() && iterator.hasNext()) {
pair = iterator.next();
leftIterator = mapper.apply(pair).iterator();
}
return leftIterator.hasNext();
}
@Override
public Pair next() {
if (!hasNext())
throw new NoSuchElementException();
return Pair.of(leftIterator.next(), pair.getRight());
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}