org.killbill.commons.utils.collect.Iterators Maven / Gradle / Ivy
/*
* Copyright (C) 2007 The Guava Authors
* Copyright 2020-2022 Equinix, Inc
* Copyright 2014-2022 The Billing Project, LLC
*
* The Billing Project 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.killbill.commons.utils.collect;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.Spliterators;
import java.util.function.Function;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
import javax.annotation.CheckForNull;
import org.killbill.commons.utils.Preconditions;
/**
* Contains subset of Guava's {@code com.google.common.collect.Iterators} functionality.
*/
public final class Iterators {
/**
* Verbatim copy of Guava's {@code com.google.common.collect.Iterators#getNext(Iterator, Object)}.
*
* Returns the next element in {@code iterator} or {@code defaultValue} if the iterator is empty.
*/
public static T getNext(final Iterator iterator, final T defaultValue) {
return iterator.hasNext() ? iterator.next() : defaultValue;
}
/**
* Verbatim copy of Guava's {@code com.google.common.collect.Iterators#getLast(Iterator)}
*
* Advances {@code iterator} to the end, returning the last element.
*
* @return the last element of {@code iterator}
* @throws NoSuchElementException if the iterator is empty
*/
public static T getLast(final Iterator iterator) {
while (true) {
final T current = iterator.next();
if (!iterator.hasNext()) {
return current;
}
}
}
/**
* Returns a view containing the result of applying {@code function} to each element of {@code fromIterator}.
*
* The returned iterator supports {@code remove()} if {@code fromIterator} does. After a
* successful {@code remove()} call, {@code fromIterator} no longer contains the corresponding
* element.
*/
public static Iterator transform(final Iterator fromIterator, final Function function) {
Preconditions.checkNotNull(function);
return new TransformedIterator(fromIterator) {
@Override
T transform(final F from) {
return function.apply(from);
}
};
}
/**
* Verbatim copy of what guava's did in {@code com.google.common.collect.ImmutableList#copyOf(Iterator)} .
*
* Returns an immutable list containing the given elements, in order.
*
* @throws NullPointerException if {@code elements} contains a null element
*/
public static List toUnmodifiableList(final Iterator elements) {
// We special-case for 0 or 1 elements, but going further is madness.
if (!elements.hasNext()) {
return Collections.emptyList();
}
final E first = elements.next();
if (!elements.hasNext()) {
return List.of(first);
} else {
final List result = new ArrayList<>();
result.add(first);
elements.forEachRemaining(result::add);
return List.copyOf(result);
}
}
/**
* Get size of {@link Iterator}. See also Guava's {@code com.google.common.collect.Iterators#size(Iterator)}.
*
* @param iterator to compute its size.
* @return the size of this iterator.
*/
public static int size(final Iterator iterator) {
int count = 0;
while (iterator.hasNext()) {
iterator.next();
count++;
}
return count;
}
/**
* Create a {@link Stream} from {@link Iterator}. Iterator first converted to {@link Spliterators} using:
* Spliterators.spliteratorUnknownSize(attributesIterator, Spliterator.ORDERED)
*
* @param iterator to transform to {@link Stream}
* @param iterator element
* @return new {@link Stream}
*/
public static Stream toStream(final Iterator iterator) {
return StreamSupport.stream(Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED), false);
}
/** Returns {@code true} if {@code iterator} contains {@code element}. */
public static boolean contains(final Iterator iterator, @CheckForNull final Object element) {
if (element == null) {
while (iterator.hasNext()) {
if (iterator.next() == null) {
return true;
}
}
} else {
while (iterator.hasNext()) {
if (element.equals(iterator.next())) {
return true;
}
}
}
return false;
}
/**
* Verbatim copy of {@code com.google.common.collect.Iterators#getLast(Iterator, Object)}.
*
* Advances {@code iterator} to the end, returning the last element or {@code defaultValue} if the iterator is empty.
*
* @param defaultValue the default value to return if the iterator is empty
* @return the last element of {@code iterator}
*/
public static T getLast(final Iterator iterator, final T defaultValue) {
return iterator.hasNext() ? getLast(iterator) : defaultValue;
}
public static Iterator concat(final Iterator> inputs) {
return new ConcatenatedIterator<>(inputs);
}
/**
* Returns the single element contained in {@code iterator}.
*
* @throws NoSuchElementException if the iterator is empty
* @throws IllegalArgumentException if the iterator contains multiple elements. The state of the
* iterator is unspecified.
*/
public static T getOnlyElement(final Iterator iterator) {
final T first = iterator.next();
if (!iterator.hasNext()) {
return first;
}
final StringBuilder sb = new StringBuilder().append("expected one element but was: <").append(first);
for (int i = 0; i < 4 && iterator.hasNext(); i++) {
sb.append(", ").append(iterator.next());
}
if (iterator.hasNext()) {
sb.append(", ...");
}
sb.append('>');
throw new IllegalArgumentException(sb.toString());
}
}