org.wikidata.wdtk.util.NestedIterator Maven / Gradle / Ivy
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package org.wikidata.wdtk.util;
/*
* #%L
* Wikidata Toolkit Utilities
* %%
* Copyright (C) 2014 Wikidata Toolkit Developers
* %%
* 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.
* #L%
*/
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* Given an iterable of iterables of T, this class simulates an iterator of T.
* For example, it can be used to iterate over every element in a list of lists
* of T.
*
* This implementation does not support the removal of elements.
*
* @author Markus Kroetzsch
*
* @param
*/
public class NestedIterator implements Iterator {
Iterator> outerIterator;
Iterator innerIterator;
/**
* Constructor.
*
* @param iterableOfIterables
* the nested iterable to iterate over
*/
public NestedIterator(Iterable> iterableOfIterables) {
this.outerIterator = iterableOfIterables.iterator();
advanceOuterIterator();
}
@Override
public boolean hasNext() {
return this.innerIterator != null;
}
@Override
public T next() {
if (this.innerIterator == null) {
throw new NoSuchElementException();
}
T result = this.innerIterator.next();
if (!this.innerIterator.hasNext()) {
advanceOuterIterator();
}
return result;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
private void advanceOuterIterator() {
while ((this.innerIterator == null || !this.innerIterator.hasNext())
&& this.outerIterator.hasNext()) {
this.innerIterator = this.outerIterator.next().iterator();
}
if (this.innerIterator != null && !this.innerIterator.hasNext()) {
this.innerIterator = null;
}
}
}