| /* |
| * Copyright (C) 2007 The Guava Authors |
| * |
| * 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 org.apache.cassandra.index.sasi.utils; |
| |
| import java.util.NoSuchElementException; |
| |
| import com.google.common.collect.PeekingIterator; |
| |
| import static com.google.common.base.Preconditions.checkState; |
| |
| // This is fork of the Guava AbstractIterator, the only difference |
| // is that state & next variables are now protected, this was required |
| // for SkippableIterator.skipTo(..) to void all previous state. |
| public abstract class AbstractIterator<T> implements PeekingIterator<T> |
| { |
| protected State state = State.NOT_READY; |
| |
| /** Constructor for use by subclasses. */ |
| protected AbstractIterator() {} |
| |
| protected 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, |
| } |
| |
| protected T next; |
| |
| /** |
| * Returns the next element. <b>Note:</b> 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. |
| * |
| * <p>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. |
| * |
| * <p>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}. |
| * |
| * <p>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 T computeNext(); |
| |
| /** |
| * Implementations of {@link #computeNext} <b>must</b> 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 T endOfData() |
| { |
| state = State.DONE; |
| return null; |
| } |
| |
| public final boolean hasNext() |
| { |
| checkState(state != State.FAILED); |
| |
| switch (state) |
| { |
| case DONE: |
| return false; |
| |
| case READY: |
| return true; |
| |
| default: |
| } |
| |
| return tryToComputeNext(); |
| } |
| |
| protected boolean tryToComputeNext() |
| { |
| state = State.FAILED; // temporary pessimism |
| next = computeNext(); |
| |
| if (state != State.DONE) |
| { |
| state = State.READY; |
| return true; |
| } |
| |
| return false; |
| } |
| |
| public final T next() |
| { |
| if (!hasNext()) |
| throw new NoSuchElementException(); |
| |
| state = State.NOT_READY; |
| return next; |
| } |
| |
| public void remove() |
| { |
| throw new UnsupportedOperationException(); |
| } |
| |
| /** |
| * Returns the next element in the iteration without advancing the iteration, |
| * according to the contract of {@link PeekingIterator#peek()}. |
| * |
| * <p>Implementations of {@code AbstractIterator} that wish to expose this |
| * functionality should implement {@code PeekingIterator}. |
| */ |
| public final T peek() |
| { |
| if (!hasNext()) |
| throw new NoSuchElementException(); |
| |
| return next; |
| } |
| } |