com.google.common.collect.AbstractSequentialIterator Maven / Gradle / Ivy
/*
* Copyright (C) 2010 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.collect;
import com.google.common.annotations.GwtCompatible;
import java.util.NoSuchElementException;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* This class provides a skeletal implementation of the {@code Iterator} interface for sequences
* whose next element can always be derived from the previous element. Null elements are not
* supported, nor is the {@link #remove()} method.
*
* Example:
*
*
{@code
* Iterator powersOfTwo =
* new AbstractSequentialIterator(1) {
* protected Integer computeNext(Integer previous) {
* return (previous == 1 << 30) ? null : previous * 2;
* }
* };
* }
*
* @author Chris Povirk
* @since 12.0 (in Guava as {@code AbstractLinkedIterator} since 8.0)
*/
@GwtCompatible
public abstract class AbstractSequentialIterator extends UnmodifiableIterator {
private @Nullable T nextOrNull;
/**
* Creates a new iterator with the given first element, or, if {@code firstOrNull} is null,
* creates a new empty iterator.
*/
protected AbstractSequentialIterator(@Nullable T firstOrNull) {
this.nextOrNull = firstOrNull;
}
/**
* Returns the element that follows {@code previous}, or returns {@code null} if no elements
* remain. This method is invoked during each call to {@link #next()} in order to compute the
* result of a future call to {@code next()}.
*/
protected abstract @Nullable T computeNext(T previous);
@Override
public final boolean hasNext() {
return nextOrNull != null;
}
@Override
public final T next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
try {
return nextOrNull;
} finally {
nextOrNull = computeNext(nextOrNull);
}
}
}