| /* |
| * 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 com.google.common.base; |
| |
| import static com.google.common.base.Preconditions.checkState; |
| |
| import com.google.common.annotations.GwtCompatible; |
| import com.google.errorprone.annotations.CanIgnoreReturnValue; |
| import java.util.Iterator; |
| import java.util.NoSuchElementException; |
| import org.checkerframework.checker.nullness.compatqual.NullableDecl; |
| |
| /** |
| * Note this class is a copy of {@link com.google.common.collect.AbstractIterator} (for dependency |
| * reasons). |
| */ |
| @GwtCompatible |
| abstract class AbstractIterator<T> implements Iterator<T> { |
| private State state = State.NOT_READY; |
| |
| protected AbstractIterator() {} |
| |
| private enum State { |
| READY, |
| NOT_READY, |
| DONE, |
| FAILED, |
| } |
| |
| @NullableDecl private T next; |
| |
| protected abstract T computeNext(); |
| |
| @CanIgnoreReturnValue |
| @NullableDecl |
| protected final T endOfData() { |
| state = State.DONE; |
| return null; |
| } |
| |
| @Override |
| public final boolean hasNext() { |
| checkState(state != State.FAILED); |
| switch (state) { |
| case READY: |
| return true; |
| case DONE: |
| return false; |
| 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 T next() { |
| if (!hasNext()) { |
| throw new NoSuchElementException(); |
| } |
| state = State.NOT_READY; |
| T result = next; |
| next = null; |
| return result; |
| } |
| |
| @Override |
| public final void remove() { |
| throw new UnsupportedOperationException(); |
| } |
| } |