org.apache.cassandra.utils.AbstractIterator Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* 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.cassandra.utils;
import com.google.common.collect.PeekingIterator;
import java.util.Iterator;
import java.util.NoSuchElementException;
public abstract class AbstractIterator implements Iterator, PeekingIterator
{
private enum State { MUST_FETCH, HAS_NEXT, DONE, FAILED }
private State state = State.MUST_FETCH;
private V next;
protected V endOfData()
{
state = State.DONE;
return null;
}
protected abstract V computeNext();
public boolean hasNext()
{
switch (state)
{
case MUST_FETCH:
state = State.FAILED;
next = computeNext();
default:
if (state == State.DONE)
return false;
state = State.HAS_NEXT;
return true;
case FAILED:
throw new IllegalStateException();
}
}
public V next()
{
if (state != State.HAS_NEXT && !hasNext())
throw new NoSuchElementException();
state = State.MUST_FETCH;
V result = next;
next = null;
return result;
}
public V peek()
{
if (!hasNext())
throw new NoSuchElementException();
return next;
}
public void remove()
{
throw new UnsupportedOperationException();
}
}