repacked.com.google.common.collect.AbstractIterator Maven / Gradle / Ivy
package repacked.com.google.common.collect;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* Copyright (C) 2010 RapidPM
* 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.
*
* Created by RapidPM - Team on 19.09.16.
*/
public abstract class AbstractIterator implements Iterator {
private State state = State.NOT_READY;
private E next;
/**
* Constructor for use by subclasses.
*/
protected AbstractIterator() {
}
/**
* Implementations of {@link #computeNext} must invoke this method when
* there are no elements left in the iteration.
*
* @return {@code null}; a convenience so your {@code computeNext}
* implementation can use the simple statement {@code return endOfData();}
*/
protected final E endOfData() {
state = State.DONE;
return null;
}
/**
* Returns the next element in the iteration without advancing the iteration,
* according to the contract of { PeekingIterator#peek()}.
*
* Implementations of {@code AbstractIterator} that wish to expose this
* functionality should implement {@code PeekingIterator}.
*/
public final E peek() {
if (!hasNext()) {
throw new NoSuchElementException();
}
return next;
} /**
* Returns the next element. Note: the implementation must call {@link
* #endOfData()} when there are no elements left in the iteration. Failure to
* do so could result in an infinite loop.
*
*
The initial invocation of {@link #hasNext()} or {@link #next()} calls
* this method, as does the first invocation of {@code hasNext} or {@code
* next} following each successful call to {@code next}. Once the
* implementation either invokes {@code endOfData} or throws an exception,
* {@code computeNext} is guaranteed to never be called again.
*
*
If this method throws an exception, it will propagate outward to the
* {@code hasNext} or {@code next} invocation that invoked this method. Any
* further attempts to use the iterator will result in an {@link
* IllegalStateException}.
*
*
The implementation of this method may not invoke the {@code hasNext},
* {@code next}, or {@link #peek()} methods on this instance; if it does, an
* {@code IllegalStateException} will result.
*
* @return the next element if there was one. If {@code endOfData} was called
* during execution, the return value will be ignored.
*
* @throws RuntimeException if any unrecoverable error happens. This exception
* will propagate outward to the {@code hasNext()}, {@code next()}, or
* {@code peek()} invocation that invoked this method. Any further
* attempts to use the iterator will result in an
* {@link IllegalStateException}.
*/
protected abstract E computeNext();
private enum State {
/**
* We have computed the next element and haven't returned it yet.
*/
READY,
/**
* We haven't yet computed or have already returned the element.
*/
NOT_READY,
/**
* We have reached the end of the data and are finished.
*/
DONE,
/**
* We've suffered an exception and are kaput.
*/
FAILED,
}
@Override
public final boolean hasNext() {
checkState(state != State.FAILED);
switch (state) {
case DONE:
return false;
case READY:
return true;
default:
}
return tryToComputeNext();
}
private boolean tryToComputeNext() {
state = State.FAILED; // temporary pessimism
next = computeNext();
if (state != State.DONE) {
state = State.READY;
return true;
}
return false;
}
@Override
public final E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
state = State.NOT_READY;
E result = next;
next = null;
return result;
}
public void checkState(boolean expression) {
if (!expression) {
throw new IllegalStateException();
}
}
}