com.github.steveash.jg2p.util.NestedLoopPairIterable Maven / Gradle / Ivy
/*
* Copyright 2014 Steve Ash
*
* 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 com.github.steveash.jg2p.util;
import com.google.common.collect.AbstractIterator;
import org.apache.commons.lang3.tuple.Pair;
import java.util.Iterator;
/**
* Allows you to lazily do a nested loop of P x Q where P is the outer and Q is the inner
*
* @author Steve Ash
*/
public class NestedLoopPairIterable implements Iterable> {
public static NestedLoopPairIterable of(Iterable outerSource, Iterable innerSource) {
return new NestedLoopPairIterable<>(outerSource, innerSource);
}
private final Iterable outerSource;
private final Iterable innerSource;
private NestedLoopPairIterable(Iterable outerSource, Iterable innerSource) {
this.outerSource = outerSource;
this.innerSource = innerSource;
}
@Override
public Iterator> iterator() {
return new AbstractIterator>() {
private final Iterator outer = outerSource.iterator();
private Iterator inner = innerSource.iterator();
private P lastOuter;
private boolean hasAtLeastOne = false;
{
// setup for the initial state
if (outer.hasNext() && inner.hasNext()) {
lastOuter = outer.next();
hasAtLeastOne = true;
}
}
@Override
protected Pair computeNext() {
if (!hasAtLeastOne) {
return endOfData();
}
if (!inner.hasNext()) {
if (!outer.hasNext()) {
return endOfData();
}
lastOuter = outer.next();
inner = innerSource.iterator();
}
return Pair.of(lastOuter, inner.next());
}
};
}
}