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This artifact provides efficient implementations for various collection data structures (esp. linked lists and priority queues), which have very insufficient implementation in the Java Collections Framework that makes it hard or even impossible to exploit their efficiencies.

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/* Copyright (C) 2013-2018 TU Dortmund
 * This file is part of AutomataLib, http://www.automatalib.net/.
 *
 * 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 net.automatalib.commons.smartcollections;

import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.Objects;

/**
 * This class eases the implementation of the {@link SmartCollection} interface. It is comparable to {@link
 * AbstractCollection} from the Java Collections Framework.
 * 
 * A class extending this abstract class has to implement the following methods: - {@link Collection#size()} - {@link
 * SmartCollection#get(ElementReference)} - {@link SmartCollection#referenceIterator()} - {@link
 * SmartCollection#referencedAdd(Object)} - {@link SmartCollection#remove(ElementReference)} - {@link
 * SmartCollection#replace(ElementReference, Object)}
 *
 * @param 
 *         element class.
 *
 * @author Malte Isberner
 */
public abstract class AbstractSmartCollection extends AbstractCollection implements SmartCollection {

    @Override
    public E choose() {
        return iterator().next();
    }

    @Override
    public ElementReference chooseRef() {
        return referenceIterator().next();
    }

    @Override
    public Iterable references() {
        return this::referenceIterator;
    }

    @Override
    public void addAll(Iterable iterable) {
        for (E e : iterable) {
            add(e);
        }
    }

    @Override
    public  void addAll(T[] array) {
        for (T t : array) {
            add(t);
        }
    }

    @Override
    public ElementReference find(Object element) {
        for (ElementReference ref : references()) {
            E current = get(ref);
            if (Objects.equals(current, element)) {
                return ref;
            }
        }

        return null;
    }

    @Override
    public void quickClear() {
        clear();
    }

    @Override
    public void deepClear() {
        clear();
    }

    @Override
    public Iterator iterator() {
        return new DeRefIterator(referenceIterator());
    }

    @Override
    public boolean add(E e) {
        referencedAdd(e);
        return true;
    }

    @Override
    public boolean remove(Object element) {
        ElementReference ref = find(element);
        if (ref == null) {
            return false;
        }
        remove(ref);
        return true;
    }

    /**
     * An iterator for iterating over the concrete elements, based on the iteration over the element references.
     */
    private class DeRefIterator implements Iterator {

        // the reference iterator
        private final Iterator refIterator;

        /**
         * Constructor.
         *
         * @param refIterator
         *         the reference iterator.
         */
        DeRefIterator(Iterator refIterator) {
            this.refIterator = refIterator;
        }

        @Override
        public boolean hasNext() {
            return refIterator.hasNext();
        }

        @Override
        public E next() {
            return get(refIterator.next());
        }

        @Override
        public void remove() {
            refIterator.remove();
        }
    }

}