Commons Collections example source code file (AbstractMapBag.java)

This example Commons Collections source code file (AbstractMapBag.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Collections tags/keywords

abstractmapbag, bag, bag, bagiterator, hashbag, io, ioexception, iterator, iterator, map, mutableinteger, mutableinteger, object, object, reflection, set, util

The Commons Collections AbstractMapBag.java source code

/*
 *  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.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: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
 * 
 * @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 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 if the bag contains all elements in
     * the given collection, respecting cardinality.
     * 
     * @param other  the bag to check against
     * @return <code>true 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 if the object was not already in the uniqueSet
     */
    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 if the object was not already in the uniqueSet
     */
    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 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.
     * 
     * @param object  the object to remove
     * @return true if the bag changed
     */
    public boolean remove(Object object) {
        MutableInteger mut = (MutableInteger) map.get(object);
        if (mut == null) {
            return false;
        }
        modCount++;
        map.remove(object);
        size -= mut.value;
        return true;
    }

    /**
     * Removes a specified number of copies of an object from the bag.
     * 
     * @param object  the object to remove
     * @param nCopies  the number of copies to remove
     * @return true if the bag changed
     */
    public boolean remove(Object object, int nCopies) {
        MutableInteger mut = (MutableInteger) map.get(object);
        if (mut == null) {
            return false;
        }
        if (nCopies <= 0) {
            return false;
        }
        modCount++;
        if (nCopies < mut.value) {
            mut.value -= nCopies;
            size -= nCopies;
        } else {
            map.remove(object);
            size -= mut.value;
        }
        return true;
    }

    /**
     * Removes objects from the bag according to their count in the specified collection.
     * 
     * @param coll  the collection to use
     * @return true if the bag changed
     */
    public boolean removeAll(Collection coll) {
        boolean result = false;
        if (coll != null) {
            Iterator i = coll.iterator();
            while (i.hasNext()) {
                boolean changed = remove(i.next(), 1);
                result = result || changed;
            }
        }
        return result;
    }

    /**
     * Remove any members of the bag that are not in the given
     * bag, respecting cardinality.
     *
     * @param coll  the collection to retain
     * @return true if this call changed the collection
     */
    public boolean retainAll(Collection coll) {
        if (coll instanceof Bag) {
            return retainAll((Bag) coll);
        }
        return retainAll(new HashBag(coll));
    }

    /**
     * Remove any members of the bag that are not in the given
     * bag, respecting cardinality.
     * @see #retainAll(Collection)
     * 
     * @param other  the bag to retain
     * @return <code>true if this call changed the collection
     */
    boolean retainAll(Bag other) {
        boolean result = false;
        Bag excess = new HashBag();
        Iterator i = uniqueSet().iterator();
        while (i.hasNext()) {
            Object current = i.next();
            int myCount = getCount(current);
            int otherCount = other.getCount(current);
            if (1 <= otherCount && otherCount <= myCount) {
                excess.add(current, myCount - otherCount);
            } else {
                excess.add(current, myCount);
            }
        }
        if (!excess.isEmpty()) {
            result = removeAll(excess);
        }
        return result;
    }

    //-----------------------------------------------------------------------
    /**
     * Mutable integer class for storing the data.
     */
    protected static class MutableInteger {
        /** The value of this mutable. */
        protected int value;
        
        /**
         * Constructor.
         * @param value  the initial value
         */
        MutableInteger(int value) {
            this.value = value;
        }
        
        public boolean equals(Object obj) {
            if (obj instanceof MutableInteger == false) {
                return false;
            }
            return ((MutableInteger) obj).value == value;
        }

        public int hashCode() {
            return value;
        }
    }
    
    //-----------------------------------------------------------------------
    /**
     * Returns an array of all of this bag's elements.
     *
     * @return an array of all of this bag's elements
     */
    public Object[] toArray() {
        Object[] result = new Object[size()];
        int i = 0;
        Iterator it = map.keySet().iterator();
        while (it.hasNext()) {
            Object current = it.next();
            for (int index = getCount(current); index > 0; index--) {
                result[i++] = current;
            }
        }
        return result;
    }

    /**
     * Returns an array of all of this bag's elements.
     *
     * @param array  the array to populate
     * @return an array of all of this bag's elements
     */
    public Object[] toArray(Object[] array) {
        int size = size();
        if (array.length < size) {
            array = (Object[]) Array.newInstance(array.getClass().getComponentType(), size);
        }

        int i = 0;
        Iterator it = map.keySet().iterator();
        while (it.hasNext()) {
            Object current = it.next();
            for (int index = getCount(current); index > 0; index--) {
                array[i++] = current;
            }
        }
        if (array.length > size) {
            array[size] = null;
        }
        return array;
    }

    /**
     * Returns an unmodifiable view of the underlying map's key set.
     *
     * @return the set of unique elements in this bag
     */
    public Set uniqueSet() {
        if (uniqueSet == null) {
            uniqueSet = UnmodifiableSet.decorate(map.keySet());
        }
        return uniqueSet;
    }

    //-----------------------------------------------------------------------
    /**
     * Write the map out using a custom routine.
     * @param out  the output stream
     * @throws IOException
     */
    protected void doWriteObject(ObjectOutputStream out) throws IOException {
        out.writeInt(map.size());
        for (Iterator it = map.entrySet().iterator(); it.hasNext();) {
            Map.Entry entry = (Map.Entry) it.next();
            out.writeObject(entry.getKey());
            out.writeInt(((MutableInteger) entry.getValue()).value);
        }
    }

    /**
     * Read the map in using a custom routine.
     * @param map  the map to use
     * @param in  the input stream
     * @throws IOException
     * @throws ClassNotFoundException
     */
    protected void doReadObject(Map map, ObjectInputStream in) throws IOException, ClassNotFoundException {
        this.map = map;
        int entrySize = in.readInt();
        for (int i = 0; i < entrySize; i++) {
            Object obj = in.readObject();
            int count = in.readInt();
            map.put(obj, new MutableInteger(count));
            size += count;
        }
    }
    
    //-----------------------------------------------------------------------
    /**
     * Compares this Bag to another.
     * This Bag equals another Bag if it contains the same number of occurrences of
     * the same elements.
     * 
     * @param object  the Bag to compare to
     * @return true if equal
     */
    public boolean equals(Object object) {
        if (object == this) {
            return true;
        }
        if (object instanceof Bag == false) {
            return false;
        }
        Bag other = (Bag) object;
        if (other.size() != size()) {
            return false;
        }
        for (Iterator it = map.keySet().iterator(); it.hasNext();) {
            Object element = it.next();
            if (other.getCount(element) != getCount(element)) {
                return false;
            }
        }
        return true;
    }

    /**
     * Gets a hash code for the Bag compatible with the definition of equals.
     * The hash code is defined as the sum total of a hash code for each element.
     * The per element hash code is defined as
     * <code>(e==null ? 0 : e.hashCode()) ^ noOccurances).
     * This hash code is compatible with the Set interface.
     * 
     * @return the hash code of the Bag
     */
    public int hashCode() {
        int total = 0;
        for (Iterator it = map.entrySet().iterator(); it.hasNext();) {
            Map.Entry entry = (Map.Entry) it.next();
            Object element = entry.getKey();
            MutableInteger count = (MutableInteger) entry.getValue();
            total += (element == null ? 0 : element.hashCode()) ^ count.value;
        }
        return total;
    }

    /**
     * Implement a toString() method suitable for debugging.
     * 
     * @return a debugging toString
     */
    public String toString() {
        if (size() == 0) {
            return "[]";
        }
        StringBuffer buf = new StringBuffer();
        buf.append('[');
        Iterator it = uniqueSet().iterator();
        while (it.hasNext()) {
            Object current = it.next();
            int count = getCount(current);
            buf.append(count);
            buf.append(':');
            buf.append(current);
            if (it.hasNext()) {
                buf.append(',');
            }
        }
        buf.append(']');
        return buf.toString();
    }
    
}