abstractmapbag.java

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/*
 *  Copyright 2002-2004 The Apache Software Foundation
 *
 *  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 org.apache.commons.collections.bag;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.reflect.Array;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import org.apache.commons.collections.Bag;
import org.apache.commons.collections.set.UnmodifiableSet;

/**
 * Abstract implementation of the {@link Bag} interface to simplify the creation
 * of subclass implementations.
 * <p>
 * Subclasses specify a Map implementation to use as the internal storage.
 * The map will be used to map bag elements to a number; the number represents
 * the number of occurrences of that element in the bag.
 *
 * @since Commons Collections 3.0 (previously DefaultMapBag v2.0)
 * @version $Revision: 219131 $ $Date: 2005-07-15 00:11:12 +0100 (Fri, 15 Jul 2005) $
 * 
 * @author Chuck Burdick
 * @author Michael A. Smith
 * @author Stephen Colebourne
 * @author Janek Bogucki
 * @author Steve Clark
 */
public abstract class AbstractMapBag implements Bag {
    
    /** The map to use to store the data */
    private transient Map map;
    /** The current total size of the bag */
    private int size;
    /** The modification count for fail fast iterators */
    private transient int modCount;
    /** The modification count for fail fast iterators */
    private transient Set uniqueSet;

    /**
     * Constructor needed for subclass serialisation.
     * 
     */
    protected AbstractMapBag() {
        super();
    }

    /**
     * Constructor that assigns the specified Map as the backing store.
     * The map must be empty and non-null.
     * 
     * @param map  the map to assign
     */
    protected AbstractMapBag(Map map) {
        super();
        this.map = map;
    }

    /**
     * Utility method for implementations to access the map that backs
     * this bag. Not intended for interactive use outside of subclasses.
     * 
     * @return the map being used by the Bag
     */
    protected Map getMap() {
        return map;
    }

    //-----------------------------------------------------------------------
    /**
     * Returns the number of elements in this bag.
     *
     * @return current size of the bag
     */
    public int size() {
        return size;
    }

    /**
     * Returns true if the underlying map is empty.
     *
     * @return true if bag is empty
     */
    public boolean isEmpty() {
        return map.isEmpty();
    }

    /**
     * Returns the number of occurrence of the given element in this bag
     * by looking up its count in the underlying map.
     *
     * @param object  the object to search for
     * @return the number of occurrences of the object, zero if not found
     */
    public int getCount(Object object) {
        MutableInteger count = (MutableInteger) map.get(object);
        if (count != null) {
            return count.value;
        }
        return 0;
    }

    //-----------------------------------------------------------------------
    /**
     * Determines if the bag contains the given element by checking if the
     * underlying map contains the element as a key.
     *
     * @param object  the object to search for
     * @return true if the bag contains the given element
     */
    public boolean contains(Object object) {
        return map.containsKey(object);
    }

    /**
     * Determines if the bag contains the given elements.
     * 
     * @param coll  the collection to check against
     * @return <code>true</code> if the Bag contains all the collection
     */
    public boolean containsAll(Collection coll) {
        if (coll instanceof Bag) {
            return containsAll((Bag) coll);
        }
        return containsAll(new HashBag(coll));
    }

    /**
     * Returns <code>true</code> if the bag contains all elements in
     * the given collection, respecting cardinality.
     * 
     * @param other  the bag to check against
     * @return <code>true</code> if the Bag contains all the collection
     */
    boolean containsAll(Bag other) {
        boolean result = true;
        Iterator it = other.uniqueSet().iterator();
        while (it.hasNext()) {
            Object current = it.next();
            boolean contains = getCount(current) >= other.getCount(current);
            result = result && contains;
        }
        return result;
    }

    //-----------------------------------------------------------------------
    /**
     * Gets an iterator over the bag elements.
     * Elements present in the Bag more than once will be returned repeatedly.
     * 
     * @return the iterator
     */
    public Iterator iterator() {
        return new BagIterator(this);
    }

    /**
     * Inner class iterator for the Bag.
     */
    static class BagIterator implements Iterator {
        private AbstractMapBag parent;
        private Iterator entryIterator;
        private Map.Entry current;
        private int itemCount;
        private final int mods;
        private boolean canRemove;

        /**
         * Constructor.
         * 
         * @param parent  the parent bag
         */
        public BagIterator(AbstractMapBag parent) {
            this.parent = parent;
            this.entryIterator = parent.map.entrySet().iterator();
            this.current = null;
            this.mods = parent.modCount;
            this.canRemove = false;
        }

        public boolean hasNext() {
            return (itemCount > 0 || entryIterator.hasNext());
        }

        public Object next() {
            if (parent.modCount != mods) {
                throw new ConcurrentModificationException();
            }
            if (itemCount == 0) {
                current = (Map.Entry) entryIterator.next();
                itemCount = ((MutableInteger) current.getValue()).value;
            }
            canRemove = true;
            itemCount--;
            return current.getKey();
        }

        public void remove() {
            if (parent.modCount != mods) {
                throw new ConcurrentModificationException();
            }
            if (canRemove == false) {
                throw new IllegalStateException();
            }
            MutableInteger mut = (MutableInteger) current.getValue();
            if (mut.value > 1) {
                mut.value--;
            } else {
                entryIterator.remove();
            }
            parent.size--;
            canRemove = false;
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Adds a new element to the bag, incrementing its count in the underlying map.
     *
     * @param object  the object to add
     * @return <code>true</code> if the object was not already in the <code>uniqueSet</code>
     */
    public boolean add(Object object) {
        return add(object, 1);
    }

    /**
     * Adds a new element to the bag, incrementing its count in the map.
     *
     * @param object  the object to search for
     * @param nCopies  the number of copies to add
     * @return <code>true</code> if the object was not already in the <code>uniqueSet</code>
     */
    public boolean add(Object object, int nCopies) {
        modCount++;
        if (nCopies > 0) {
            MutableInteger mut = (MutableInteger) map.get(object);
            size += nCopies;
            if (mut == null) {
                map.put(object, new MutableInteger(nCopies));
                return true;
            } else {
                mut.value += nCopies;
                return false;
            }
        } else {
            return false;
        }
    }

    /**
     * Invokes {@link #add(Object)} for each element in the given collection.
     *
     * @param coll  the collection to add
     * @return <code>true</code> if this call changed the bag
     */
    public boolean addAll(Collection coll) {
        boolean changed = false;
        Iterator i = coll.iterator();
        while (i.hasNext()) {
            boolean added = add(i.next());
            changed = changed || added;
        }
        return changed;
    }

    //-----------------------------------------------------------------------
    /**
     * Clears the bag by clearing the underlying map.
     */
    public void clear() {
        modCount++;
        map.clear();
        size = 0;
    }

    /**
     * Removes all copies of the specified object from the bag.