src/main/java/org/apache/sling/query/AbstractQuery.java

/*-
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.apache.sling.query;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

import org.apache.sling.query.api.SearchStrategy;
import org.apache.sling.query.api.internal.IteratorToIteratorFunction;
import org.apache.sling.query.api.internal.Option;
import org.apache.sling.query.api.internal.TreeProvider;
import org.apache.sling.query.impl.function.AddFunction;
import org.apache.sling.query.impl.function.ChildrenFunction;
import org.apache.sling.query.impl.function.ClosestFunction;
import org.apache.sling.query.impl.function.CompositeFunction;
import org.apache.sling.query.impl.function.DescendantFunction;
import org.apache.sling.query.impl.function.FilterFunction;
import org.apache.sling.query.impl.function.FindFunction;
import org.apache.sling.query.impl.function.HasFunction;
import org.apache.sling.query.impl.function.IdentityFunction;
import org.apache.sling.query.impl.function.LastFunction;
import org.apache.sling.query.impl.function.NextFunction;
import org.apache.sling.query.impl.function.NotFunction;
import org.apache.sling.query.impl.function.ParentFunction;
import org.apache.sling.query.impl.function.ParentsFunction;
import org.apache.sling.query.impl.function.PrevFunction;
import org.apache.sling.query.impl.function.SiblingsFunction;
import org.apache.sling.query.impl.function.SliceFunction;
import org.apache.sling.query.impl.function.UniqueFunction;
import org.apache.sling.query.impl.iterator.EmptyElementFilter;
import org.apache.sling.query.impl.iterator.OptionDecoratingIterator;
import org.apache.sling.query.impl.iterator.OptionStrippingIterator;
import org.apache.sling.query.impl.predicate.IterableContainsPredicate;
import org.apache.sling.query.impl.predicate.RejectingPredicate;
import org.apache.sling.query.impl.selector.SelectorFunction;
import org.apache.sling.query.impl.util.LazyList;
import org.osgi.annotation.versioning.ProviderType;

@ProviderType
public abstract class AbstractQuery<T, Q extends AbstractQuery<T, Q>> implements Iterable<T> {

    protected final List<Function<?, ?>> functions = new ArrayList<>();

    private final List<T> initialCollection;

    private final SearchStrategy searchStrategy;

    private final TreeProvider<T> provider;

    AbstractQuery(TreeProvider<T> provider, T[] initialCollection, SearchStrategy strategy) {
        this.provider = provider;
        this.initialCollection = new ArrayList<>(Arrays.asList(initialCollection));
        this.searchStrategy = strategy;
    }

    protected AbstractQuery(AbstractQuery<T, Q> original, SearchStrategy searchStrategy) {
        this.functions.addAll(original.functions);
        this.initialCollection = new ArrayList<>(original.initialCollection);
        this.searchStrategy = searchStrategy;
        this.provider = original.provider;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Iterator<T> iterator() {
        IteratorToIteratorFunction<T> f = new CompositeFunction<>(functions);
        Iterator<Option<T>> iterator = f.apply(new OptionDecoratingIterator<>(initialCollection.iterator()));
        iterator = new EmptyElementFilter<>(iterator);
        return new OptionStrippingIterator<>(iterator);
    }

    public Stream<T> stream() {
        return StreamSupport.stream(this.spliterator(), false);
    }

    /**
     * Include resources to the collection.
     * 
     * @param resources
     *            Resources to include
     * @return new SlingQuery object transformed by this operation
     */
    public Q add(T... resources) {
        return function(new AddFunction<>(Arrays.asList(resources)));
    }

    /**
     * Include resources to the collection.
     * 
     * @param iterable
     *            Resources to include
     * @return new SlingQuery object transformed by this operation
     */
    public Q add(Iterable<T> iterable) {
        return function(new AddFunction<>(iterable));
    }

    /**
     * Transform SlingQuery collection into a lazy list.
     * 
     * @return List containing all elements from the collection.
     */
    public List<T> asList() {
        return new LazyList<>(iterator());
    }

    /**
     * Get list of the children for each Resource in the collection.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q children() {
        return function(new ChildrenFunction<>(provider));
    }

    /**
     * Get list of the children for each Resource in the collection.
     * 
     * @param filter
     *            Children filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q children(String filter) {
        return function(new ChildrenFunction<>(provider), filter);
    }

    /**
     * Get list of the children for each Resource in the collection.
     * 
     * @param filter
     *            Children filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q children(Predicate<T> filter) {
        return function(new ChildrenFunction<>(provider), filter);
    }

    /**
     * Get list of the children for each Resource in the collection.
     * 
     * @param filter
     *            Children filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q children(Iterable<T> filter) {
        return function(new ChildrenFunction<>(provider), filter);
    }

    /**
     * For each Resource in the collection, return the first element matching the
     * selector testing the Resource itself and traversing up its ancestors.
     * 
     * @param selector
     *            Ancestor filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q closest(String selector) {
        return closest(parse(selector));
    }

    /**
     * For each Resource in the collection, return the first element matching the
     * selector testing the Resource itself and traversing up its ancestors.
     * 
     * @param iterable
     *            Ancestor filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q closest(Iterable<T> iterable) {
        return closest(new IterableContainsPredicate<>(iterable, provider));
    }

    /**
     * For each Resource in the collection, return the first element matching the
     * selector testing the Resource itself and traversing up its ancestors.
     * 
     * @param predicate
     *            Ancestor filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q closest(Predicate<T> predicate) {
        return function(new ClosestFunction<>(predicate, provider));
    }

    /**
     * Reduce Resource collection to the one Resource at the given 0-based index.
     * 
     * @param index
     *            0-based index
     * @return new SlingQuery object transformed by this operation
     */
    public Q eq(int index) {
        return slice(index, index);
    }

    /**
     * Filter Resource collection using given selector.
     * 
     * @param selector
     *            Selector
     * @return new SlingQuery object transformed by this operation
     */
    public Q filter(String selector) {
        return function(new IdentityFunction<T>(), selector);
    }

    /**
     * Filter Resource collection using given predicate object.
     * 
     * @param predicate
     *            Collection filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q filter(Predicate<T> predicate) {
        return function(new FilterFunction<>(predicate));
    }

    /**
     * Filter Resource collection using given iterable.
     * 
     * @param iterable
     *            Collection filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q filter(Iterable<T> iterable) {
        return function(new FilterFunction<>(new IterableContainsPredicate<>(iterable, provider)));
    }

    /**
     * For each Resource in collection use depth-first search to return all its
     * descendants. Please notice that invoking this method on a Resource being a
     * root of a large subtree may and will cause performance problems.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q find() {
        return function(new FindFunction<>(searchStrategy, provider, ""));
    }

    /**
     * For each Resource in collection use breadth-first search to return all its
     * descendants. Please notice that invoking this method on a Resource being a
     * root of a large subtree may and will cause performance problems.
     * 
     * @param selector
     *            descendants filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q find(String selector) {
        return function(new FindFunction<>(searchStrategy, provider, selector), selector);
    }

    /**
     * For each Resource in collection use breadth-first search to return all its
     * descendants. Please notice that invoking this method on a Resource being a
     * root of a large subtree may and will cause performance problems.
     * 
     * @param predicate
     *            descendants filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q find(Predicate<T> predicate) {
        return function(new FindFunction<>(searchStrategy, provider, ""), predicate);
    }

    /**
     * For each Resource in collection use breadth-first search to return all its
     * descendants. Please notice that invoking this method on a Resource being a
     * root of a large subtree may and will cause performance problems.
     * 
     * @param iterable
     *            descendants filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q find(Iterable<T> iterable) {
        return function(new DescendantFunction<>(new LazyList<>(iterable.iterator()), provider));
    }

    /**
     * Filter Resource collection to the first element. Equivalent to {@code eq(0)}
     * or {@code slice(0, 0)}.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q first() {
        return eq(0);
    }

    /**
     * Pick such Resources from the collection that have descendant matching the
     * selector.
     * 
     * @param selector
     *            Descendant selector
     * @return new SlingQuery object transformed by this operation
     */
    public Q has(String selector) {
        return function(new HasFunction<>(selector, searchStrategy, provider));
    }

    /**
     * Pick such Resources from the collection that have descendant matching the
     * selector.
     * 
     * @param predicate
     *            Descendant selector
     * @return new SlingQuery object transformed by this operation
     */
    public Q has(Predicate<T> predicate) {
        return function(new HasFunction<>(predicate, searchStrategy, provider));
    }

    /**
     * Pick such Resources from the collection that have descendant matching the
     * selector.
     * 
     * @param iterable
     *            Descendant selector
     * @return new SlingQuery object transformed by this operation
     */
    public Q has(Iterable<T> iterable) {
        return function(new HasFunction<>(iterable, provider));
    }

    /**
     * Filter Resource collection to the last element.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q last() {
        return function(new LastFunction<T>());
    }

    /**
     * Return the next sibling for each Resource in the collection.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q next() {
        return function(new NextFunction<>(provider));
    }

    /**
     * Return the next sibling for each Resource in the collection and filter it by
     * a selector. If the next sibling doesn't match it, empty collection will be
     * returned.
     * 
     * @param selector
     *            Next sibling filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q next(String selector) {
        return function(new NextFunction<>(provider), selector);
    }

    /**
     * Return the next sibling for each Resource in the collection and filter it by
     * a selector. If the next sibling doesn't match it, empty collection will be
     * returned.
     * 
     * @param predicate
     *            Next sibling filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q next(Predicate<T> predicate) {
        return function(new NextFunction<>(provider), predicate);
    }

    /**
     * Return the next sibling for each Resource in the collection and filter it by
     * a selector. If the next sibling doesn't match it, empty collection will be
     * returned.
     * 
     * @param iterable
     *            Next sibling filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q next(Iterable<T> iterable) {
        return function(new NextFunction<>(provider), iterable);
    }

    /**
     * Return all following siblings for each Resource in the collection.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q nextAll() {
        return function(new NextFunction<>(new RejectingPredicate<>(), provider));
    }

    /**
     * Return all following siblings for each Resource in the collection, filtering
     * them by a selector.
     * 
     * @param selector
     *            Following siblings filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q nextAll(String selector) {
        return function(new NextFunction<>(new RejectingPredicate<>(), provider), selector);
    }

    /**
     * Return all following siblings for each Resource in the collection, filtering
     * them by a selector.
     * 
     * @param predicate
     *            Following siblings filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q nextAll(Predicate<T> predicate) {
        return function(new NextFunction<>(new RejectingPredicate<>(), provider), predicate);
    }

    /**
     * Return all following siblings for each Resource in the collection, filtering
     * them by a selector.
     * 
     * @param iterable
     *            Following siblings filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q nextAll(Iterable<T> iterable) {
        return function(new NextFunction<>(new RejectingPredicate<>(), provider), iterable);
    }

    /**
     * Return all following siblings for each Resource in the collection up to, but
     * not including, Resource matched by a selector.
     * 
     * @param until
     *            Selector marking when the operation should stop
     * @return new SlingQuery object transformed by this operation
     */
    public Q nextUntil(String until) {
        return function(new NextFunction<>(parse(until), provider));
    }

    /**
     * Return all following siblings for each Resource in the collection up to, but
     * not including, Resource matched by a selector.
     * 
     * @param predicate
     *            Selector marking when the operation should stop
     * @return new SlingQuery object transformed by this operation
     */
    public Q nextUntil(Predicate<T> predicate) {
        return function(new NextFunction<>(predicate, provider));
    }

    /**
     * Return all following siblings for each Resource in the collection up to, but
     * not including, Resource matched by a selector.
     * 
     * @param iterable
     *            Selector marking when the operation should stop
     * @return new SlingQuery object transformed by this operation
     */
    public Q nextUntil(Iterable<T> iterable) {
        return nextUntil(new IterableContainsPredicate<>(iterable, provider));
    }

    /**
     * Remove elements from the collection.
     * 
     * @param selector
     *            Selector used to remove Resources
     * @return new SlingQuery object transformed by this operation
     */
    public Q not(String selector) {
        return function(new NotFunction<>(parse(selector)));
    }

    /**
     * Remove elements from the collection.
     * 
     * @param predicate
     *            Selector used to remove Resources
     * @return new SlingQuery object transformed by this operation
     */
    public Q not(Predicate<T> predicate) {
        return function(new FilterFunction<>(new RejectingPredicate<>(predicate)));
    }

    /**
     * Remove elements from the collection.
     * 
     * @param iterable
     *            Selector used to remove Resources
     * @return new SlingQuery object transformed by this operation
     */
    public Q not(Iterable<T> iterable) {
        return not(new IterableContainsPredicate<>(iterable, provider));
    }

    /**
     * Replace each element in the collection with its parent.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q parent() {
        return function(new ParentFunction<>(provider));
    }

    /**
     * For each element in the collection find its all ancestor.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q parents() {
        return function(new ParentsFunction<>(new RejectingPredicate<>(), provider));
    }

    /**
     * For each element in the collection find its all ancestor, filtered by a
     * selector.
     * 
     * @param selector
     *            Parents filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q parents(String selector) {
        return function(new ParentsFunction<>(new RejectingPredicate<>(), provider), selector);
    }

    /**
     * For each element in the collection find its all ancestor, filtered by a
     * selector.
     * 
     * @param predicate
     *            Parents filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q parents(Predicate<T> predicate) {
        return function(new ParentsFunction<>(new RejectingPredicate<>(), provider), predicate);
    }

    /**
     * For each element in the collection find its all ancestor, filtered by a
     * selector.
     * 
     * @param iterable
     *            Parents filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q parents(Iterable<T> iterable) {
        return function(new ParentsFunction<>(new RejectingPredicate<>(), provider), iterable);
    }

    /**
     * For each element in the collection find all of its ancestors until the
     * predicate is met.
     * 
     * @param until
     *            Selector marking when the operation should stop
     * @return new SlingQuery object transformed by this operation
     */
    public Q parentsUntil(String until) {
        return function(new ParentsFunction<>(parse(until), provider));
    }

    /**
     * For each element in the collection find all of its ancestors until the
     * predicate is met.
     * 
     * @param predicate
     *            Selector marking when the operation should stop
     * @return new SlingQuery object transformed by this operation
     */
    public Q parentsUntil(Predicate<T> predicate) {
        return function(new ParentsFunction<>(predicate, provider));
    }

    /**
     * For each element in the collection find all of its ancestors until the
     * predicate is met.
     * 
     * @param iterable
     *            Selector marking when the operation should stop
     * @return new SlingQuery object transformed by this operation
     */
    public Q parentsUntil(Iterable<T> iterable) {
        return parentsUntil(new IterableContainsPredicate<>(iterable, provider));
    }

    /**
     * Return the previous sibling for each Resource in the collection.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q prev() {
        return function(new PrevFunction<>(provider));
    }

    /**
     * Return the previous sibling for each Resource in the collection and filter it
     * by a selector. If the previous sibling doesn't match it, empty collection
     * will be returned.
     * 
     * @param selector
     *            Previous sibling filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q prev(String selector) {
        return function(new PrevFunction<>(null, provider), selector);
    }

    /**
     * Return the previous sibling for each Resource in the collection and filter it
     * by a selector. If the previous sibling doesn't match it, empty collection
     * will be returned.
     * 
     * @param predicate
     *            Previous sibling filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q prev(Predicate<T> predicate) {
        return function(new PrevFunction<>(null, provider), predicate);
    }

    /**
     * Return the previous sibling for each Resource in the collection and filter it
     * by a selector. If the previous sibling doesn't match it, empty collection
     * will be returned.
     * 
     * @param iterable
     *            Previous sibling filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q prev(Iterable<T> iterable) {
        return function(new PrevFunction<>(null, provider), iterable);
    }

    /**
     * Return all previous siblings for each Resource in the collection.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q prevAll() {
        return function(new PrevFunction<>(new RejectingPredicate<>(), provider));
    }

    /**
     * Return all previous siblings for each Resource in the collection, filtering
     * them by a selector.
     * 
     * @param selector
     *            Previous siblings filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q prevAll(String selector) {
        return function(new PrevFunction<>(new RejectingPredicate<>(), provider), selector);
    }

    /**
     * Return all previous siblings for each Resource in the collection, filtering
     * them by a selector.
     * 
     * @param predicate
     *            Previous siblings filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q prevAll(Predicate<T> predicate) {
        return function(new PrevFunction<>(new RejectingPredicate<>(), provider), predicate);
    }

    /**
     * Return all previous siblings for each Resource in the collection, filtering
     * them by a selector.
     * 
     * @param iterable
     *            Previous siblings filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q prevAll(Iterable<T> iterable) {
        return function(new PrevFunction<>(new RejectingPredicate<>(), provider), iterable);
    }

    /**
     * Return all previous siblings for each Resource in the collection up to, but
     * not including, Resource matched by a selector.
     * 
     * @param until
     *            Selector marking when the operation should stop
     * @return new SlingQuery object transformed by this operation
     */
    public Q prevUntil(String until) {
        return function(new PrevFunction<>(parse(until), provider));
    }

    /**
     * Return all previous siblings for each Resource in the collection up to, but
     * not including, Resource matched by a selector.
     * 
     * @param predicate
     *            Selector marking when the operation should stop
     * @return new SlingQuery object transformed by this operation
     */
    public Q prevUntil(Predicate<T> predicate) {
        return function(new PrevFunction<>(predicate, provider));
    }

    /**
     * Return all previous siblings for each Resource in the collection up to, but
     * not including, Resource matched by a selector.
     * 
     * @param iterable
     *            Selector marking when the operation should stop
     * @return new SlingQuery object transformed by this operation
     */
    public Q prevUntil(Iterable<T> iterable) {
        return prevUntil(new IterableContainsPredicate<>(iterable, provider));
    }

    /**
     * Set new search strategy, which will be used in {@link AbstractQuery#find()}
     * and {@link AbstractQuery#has(String)} functions.
     * 
     * @param strategy
     *            Search strategy type
     * @return new SlingQuery object transformed by this operation
     */
    public Q searchStrategy(SearchStrategy strategy) {
        return clone(this, strategy);
    }

    /**
     * Return siblings for the given Ts.
     * 
     * @return new SlingQuery object transformed by this operation
     */
    public Q siblings() {
        return siblings("");
    }

    /**
     * Return siblings for the given Resources filtered by a selector.
     * 
     * @param selector
     *            Siblings filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q siblings(String selector) {
        return function(new SiblingsFunction<>(provider), selector);
    }

    /**
     * Return siblings for the given Resources filtered by a selector.
     * 
     * @param predicate
     *            Siblings filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q siblings(Predicate<T> predicate) {
        return function(new SiblingsFunction<>(provider), predicate);
    }

    /**
     * Return siblings for the given Resources filtered by a selector.
     * 
     * @param iterable
     *            Siblings filter
     * @return new SlingQuery object transformed by this operation
     */
    public Q siblings(Iterable<T> iterable) {
        return function(new SiblingsFunction<>(provider), iterable);
    }

    /**
     * Filter out first {@code from} Resources from the collection.
     * 
     * @param from
     *            How many Resources to cut out
     * @return new SlingQuery object transformed by this operation
     */
    public Q slice(int from) {
        if (from < 0) {
            throw new IndexOutOfBoundsException();
        }
        return function(new SliceFunction<T>(from));
    }

    /**
     * Reduce the collection to a subcollection specified by a given range. Both
     * from and to are inclusive, 0-based indices.
     * 
     * @param from
     *            Low endpoint (inclusive) of the subcollection
     * @param to
     *            High endpoint (inclusive) of the subcollection
     * @return new SlingQuery object transformed by this operation
     */
    public Q slice(int from, int to) {
        if (from < 0) {
            throw new IndexOutOfBoundsException();
        }
        if (from > to) {
            throw new IllegalArgumentException();
        }
        return function(new SliceFunction<T>(from, to));
    }

    /**
     * Filter out repeated resources. The implementation of this method uses a
     * {@link HashSet} to store the processed elements, which may result in an
     * increased memory usage for the big collections.
     *
     * @return new SlingQuery object transformed by this operation
     */
    public Q unique() {
        return function(new UniqueFunction<>());
    }

    private Q function(Function<?, ?> function, Iterable<T> iterable) {
        Q newQuery = clone(this, this.searchStrategy);
        newQuery.functions.add(function);
        newQuery.functions.add(new FilterFunction<>(new IterableContainsPredicate<>(iterable, provider)));
        return newQuery;
    }

    private Q function(Function<?, ?> function, Predicate<T> predicate) {
        Q newQuery = clone(this, this.searchStrategy);
        newQuery.functions.add(function);
        newQuery.functions.add(new FilterFunction<>(predicate));
        return newQuery;
    }

    private Q function(Function<?, ?> function, String selector) {
        Q newQuery = clone(this, this.searchStrategy);
        newQuery.functions.add(function);
        newQuery.functions.add(new SelectorFunction<>(selector, provider, searchStrategy));
        return newQuery;
    }

    private Q function(Function<?, ?> function) {
        Q newQuery = clone(this, this.searchStrategy);
        newQuery.functions.add(function);
        return newQuery;
    }

    private SelectorFunction<T> parse(String selector) {
        return new SelectorFunction<>(selector, provider, searchStrategy);
    }

    protected abstract Q clone(AbstractQuery<T, Q> original, SearchStrategy strategy);

    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder();
        builder.append("$(");
        Iterator<T> iterator = this.iterator();
        while (iterator.hasNext()) {
            builder.append('[');
            builder.append(iterator.next());
            builder.append(']');
            if (iterator.hasNext()) {
                builder.append(", ");
            }
        }
        builder.append(")");
        return builder.toString();
    }
}