org.apache.sshd.common.util.helper.LazyIterablesConcatenator Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.sshd.common.util.helper;
import java.util.Collections;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* Creates a "smooth" wrapping {@link Iterable} using several underlying ones to provide the values. The
* "lazy" denomination is due to the fact that no iterable is consulted until the one(s) before it have been
* fully exhausted.
*
* @param Type of element being iterared
* @author Apache MINA SSHD Project
*/
public class LazyIterablesConcatenator implements Iterable {
private final Iterable> iterables;
public LazyIterablesConcatenator(Iterable> iterables) {
this.iterables = iterables;
}
public Iterable> getIterables() {
return iterables;
}
@Override
public Iterator iterator() {
return new Iterator() {
@SuppressWarnings("synthetic-access")
private final Iterator> itit
= (iterables == null) ? Collections.emptyIterator() : iterables.iterator();
private Iterator currentIterator;
private boolean finished;
@Override
public boolean hasNext() {
if (finished) {
return false;
}
// Do we have a current iterator, and if so does it still have values in it
if ((currentIterator != null) && currentIterator.hasNext()) {
return true;
}
while (itit.hasNext()) {
Iterable currentIterable = itit.next();
currentIterator = currentIterable.iterator();
if (currentIterator.hasNext()) {
return true;
}
}
// exhausted all
finished = true;
return false;
}
@Override
public T next() {
if (finished) {
throw new NoSuchElementException("All elements have been exhausted");
}
if (currentIterator == null) {
throw new IllegalStateException("'next()' called without a preceding 'hasNext()' query");
}
return currentIterator.next();
}
@Override
public String toString() {
return Iterator.class.getSimpleName() + "[lazy-concat]";
}
};
}
@Override
public String toString() {
return Iterable.class.getSimpleName() + "[lazy-concat]";
}
/**
* @param Type if iterated element
* @param iterables The iterables to concatenate - ignored if {@code null}
* @return An {@link Iterable} that goes over all the elements in the wrapped iterables one after the
* other. The denomination "lazy" indicates that no iterable is consulted until the
* previous one has been fully exhausted.
*/
public static Iterable lazyConcatenateIterables(Iterable> iterables) {
return (iterables == null) ? Collections.emptyList() : new LazyIterablesConcatenator<>(iterables);
}
}