com.mysema.util.MultiIterator Maven / Gradle / Ivy
/*
* Copyright 2011, Mysema Ltd
*
* 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.mysema.util;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import javax.annotation.Nullable;
/**
* MultiIterator provides a cartesian view on the given iterators
*
*
* e.g. (1,2) and (100, 200, 300)
* are expanded to (1, 100) (1, 200) (1, 300) (2, 100) (2, 200) (2, 300)
*
*
* @author tiwe
*/
public class MultiIterator implements Iterator {
@Nullable
private Boolean hasNext;
private int index = 0;
private final List> iterables;
private final List> iterators;
private final boolean[] lastEntry;
private final Object[] values;
public MultiIterator(List> iterables) {
this.iterables = iterables;
this.iterators = new ArrayList>(iterables.size());
for (int i = 0; i < iterables.size(); i++) {
iterators.add(null);
}
this.lastEntry = new boolean[iterables.size()];
this.values = new Object[iterables.size()];
}
@Override
public boolean hasNext() {
while (hasNext == null) {
produceNext();
}
return hasNext.booleanValue();
}
@Override
@SuppressWarnings("unchecked")
public T[] next() {
while (hasNext == null) {
produceNext();
}
if (hasNext.booleanValue()) {
hasNext = null;
return (T[]) values.clone();
} else {
throw new NoSuchElementException();
}
}
private void produceNext() {
for (int i = index; i < iterables.size(); i++) {
if (iterators.get(i) == null || (!iterators.get(i).hasNext() && i > 0)) {
iterators.set(i, iterables.get(i).iterator());
}
if (!iterators.get(i).hasNext()) {
hasNext = i == 0 ? Boolean.FALSE : null;
return;
}
values[i] = iterators.get(i).next();
lastEntry[i] = !iterators.get(i).hasNext();
hasNext = Boolean.TRUE;
}
index = iterables.size() - 1;
while (lastEntry[index] && index > 0) {
index--;
}
}
@Override
public void remove() {
// do nothing
}
}