/*******************************************************************************
* Copyright 2012 Analog Devices, Inc.
*
* 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.analog.lyric.collect;
import java.util.Collection;
import java.util.Iterator;
import org.eclipse.jdt.annotation.Nullable;
public class ReleasableIterators
{
private static final class Wrapper<T> implements ReleasableIterator<T>
{
private @Nullable Iterator<T> _iter;
private Wrapper(Iterator<T> iter)
{
_iter = iter;
}
private static final ThreadLocal<Wrapper<?>> instance = new ThreadLocal<Wrapper<?>>();
static <T> Wrapper<T> make(Iterator<T> iter)
{
@SuppressWarnings("unchecked")
Wrapper<T> wrapper = (Wrapper<T>)Wrapper.instance.get();
if (wrapper != null)
{
Wrapper.instance.set(null);
wrapper.reset(iter);
}
else
{
wrapper = new Wrapper<T>(iter);
}
return wrapper;
}
public void reset(Iterator<T> iter)
{
this._iter = iter;
}
@SuppressWarnings("null")
@Override
public boolean hasNext()
{
return this._iter.hasNext();
}
@SuppressWarnings("null")
@Override
public T next()
{
return this._iter.next();
}
@SuppressWarnings("null")
@Override
public void remove()
{
this._iter.remove();
}
@Override
public void release()
{
if (instance.get() == null)
{
_iter = null;
instance.set(this);
}
}
}
private static enum EmptyReleasableIterator implements ReleasableIterator<Object>
{
INSTANCE;
@Override
public boolean hasNext()
{
return false;
}
@Override
public @Nullable Object next()
{
return null;
}
@Override
public void remove()
{
throw new UnsupportedOperationException("remove");
}
@Override
public void release()
{
}
}
/**
* @deprecated Use #emptyIterator instead
*/
@Deprecated
@SuppressWarnings("unchecked")
public static <T> ReleasableIterator<T> emptyIterators()
{
return (ReleasableIterator<T>) EmptyReleasableIterator.INSTANCE;
}
/**
* Returns a canonical empty releasable iterator.
* <p>
* Returns an iterator whose {@linkplain Iterator#hasNext hasNext()} method returns false,
* and whose {@linkplain Iterator#next next()} method returns null.
* <p>
* @since 0.08
*/
@SuppressWarnings("unchecked")
public static <T> ReleasableIterator<T> emptyIterator()
{
return (ReleasableIterator<T>) EmptyReleasableIterator.INSTANCE;
}
/**
* Returns a {@link ReleasableIterator} for given collection.
* <p>
* This should only be used for situations in which the caller may encounter
* some collections that return {@link ReleasableIterator}s and some that do
* not and you want to avoid an explicit {@code instanceof} check.
*/
public static <T> ReleasableIterator<T> iteratorFor(Collection<T> c)
{
Iterator<T> iter = c.iterator();
if (iter instanceof ReleasableIterator)
{
return (ReleasableIterator<T>)iter;
}
return Wrapper.make(iter);
}
}