/*
 * 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.collections4.map;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Map;

import org.apache.commons.collections4.BoundedMap;

A Map implementation with a fixed maximum size which removes
the least recently used entry if an entry is added when full.

The least recently used algorithm works on the get and put operations only.
Iteration of any kind, including setting the value by iteration, does not
change the order. Queries such as containsKey and containsValue or access
via views also do not change the order.

 A somewhat subtle ramification of the least recently used algorithm is that calls to get(Object) stand a very good chance of modifying the map's iteration order and thus invalidating any iterators currently in use. It is therefore suggested that iterations over an LRUMap instance access entry values only through a MapIterator or AbstractHashedMap.entrySet() iterator. 

The map implements OrderedMap and entries may be queried using
the bidirectional OrderedMapIterator. The order returned is
least recently used to most recently used. Iterators from map views can
also be cast to OrderedIterator if required.


All the available iterators can be reset back to the start by casting to
ResettableIterator and calling reset().


Note that LRUMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using Collections.synchronizedMap(Map<Object,Object>). This class may throw NullPointerException's when accessed by concurrent threads.

Type parameters:
<K> – the type of the keys in this map
<V> – the type of the values in this map
Since:
3.0 (previously in main package v1.0)/**
 * A <code>Map</code> implementation with a fixed maximum size which removes
 * the least recently used entry if an entry is added when full.
 * <p>
 * The least recently used algorithm works on the get and put operations only.
 * Iteration of any kind, including setting the value by iteration, does not
 * change the order. Queries such as containsKey and containsValue or access
 * via views also do not change the order.
 * </p>
 * <p>
 * A somewhat subtle ramification of the least recently used
 * algorithm is that calls to {@link #get(Object)} stand a very good chance
 * of modifying the map's iteration order and thus invalidating any
 * iterators currently in use.  It is therefore suggested that iterations
 * over an {@link LRUMap} instance access entry values only through a
 * {@link org.apache.commons.collections4.MapIterator MapIterator} or {@link #entrySet()} iterator.
 * </p>
 * <p>
 * The map implements <code>OrderedMap</code> and entries may be queried using
 * the bidirectional <code>OrderedMapIterator</code>. The order returned is
 * least recently used to most recently used. Iterators from map views can
 * also be cast to <code>OrderedIterator</code> if required.
 * </p>
 * <p>
 * All the available iterators can be reset back to the start by casting to
 * <code>ResettableIterator</code> and calling <code>reset()</code>.
 * </p>
 * <p>
 * <strong>Note that LRUMap is not synchronized and is not thread-safe.</strong>
 * If you wish to use this map from multiple threads concurrently, you must use
 * appropriate synchronization. The simplest approach is to wrap this map
 * using {@link java.util.Collections#synchronizedMap(Map)}. This class may throw
 * <code>NullPointerException</code>'s when accessed by concurrent threads.
 * </p>
 *
 * @param <K> the type of the keys in this map
 * @param <V> the type of the values in this map
 * @since 3.0 (previously in main package v1.0)
 */
public class LRUMap<K, V>
        extends AbstractLinkedMap<K, V> implements BoundedMap<K, V>, Serializable, Cloneable {

    
Serialisation version /** Serialisation version */
    private static final long serialVersionUID = -612114643488955218L;
    
Default maximum size /** Default maximum size */
    protected static final int DEFAULT_MAX_SIZE = 100;

    
Maximum size /** Maximum size */
    private transient int maxSize;
    
Scan behaviour /** Scan behaviour */
    private boolean scanUntilRemovable;

    
Constructs a new empty map with a maximum size of 100.
/**
     * Constructs a new empty map with a maximum size of 100.
     */
    public LRUMap() {
        this(DEFAULT_MAX_SIZE, DEFAULT_LOAD_FACTOR, false);
    }

    
Constructs a new, empty map with the specified maximum size.
Params:
maxSize –  the maximum size of the map
Throws:
IllegalArgumentException – if the maximum size is less than one/**
     * Constructs a new, empty map with the specified maximum size.
     *
     * @param maxSize  the maximum size of the map
     * @throws IllegalArgumentException if the maximum size is less than one
     */
    public LRUMap(final int maxSize) {
        this(maxSize, DEFAULT_LOAD_FACTOR);
    }

    
Constructs a new, empty map with the specified maximum size.
Params:
maxSize –  the maximum size of the map
initialSize –  the initial size of the map
Throws:
IllegalArgumentException – if the maximum size is less than one
IllegalArgumentException – if the initial size is negative or larger than the maximum size
Since:
4.1/**
     * Constructs a new, empty map with the specified maximum size.
     *
     * @param maxSize  the maximum size of the map
     * @param initialSize  the initial size of the map
     * @throws IllegalArgumentException if the maximum size is less than one
     * @throws IllegalArgumentException if the initial size is negative or larger than the maximum size
     * @since 4.1
     */
    public LRUMap(final int maxSize, final int initialSize) {
        this(maxSize, initialSize, DEFAULT_LOAD_FACTOR);
    }

    
Constructs a new, empty map with the specified maximum size.
Params:
maxSize –  the maximum size of the map
scanUntilRemovable –  scan until a removeable entry is found, default false
Throws:
IllegalArgumentException – if the maximum size is less than one
Since:
3.1/**
     * Constructs a new, empty map with the specified maximum size.
     *
     * @param maxSize  the maximum size of the map
     * @param scanUntilRemovable  scan until a removeable entry is found, default false
     * @throws IllegalArgumentException if the maximum size is less than one
     * @since 3.1
     */
    public LRUMap(final int maxSize, final boolean scanUntilRemovable) {
        this(maxSize, DEFAULT_LOAD_FACTOR, scanUntilRemovable);
    }

    
Constructs a new, empty map with the specified max capacity and
load factor.
Params:
maxSize –  the maximum size of the map
loadFactor –  the load factor
Throws:
IllegalArgumentException – if the maximum size is less than one
IllegalArgumentException – if the load factor is less than zero/**
     * Constructs a new, empty map with the specified max capacity and
     * load factor.
     *
     * @param maxSize  the maximum size of the map
     * @param loadFactor  the load factor
     * @throws IllegalArgumentException if the maximum size is less than one
     * @throws IllegalArgumentException if the load factor is less than zero
     */
    public LRUMap(final int maxSize, final float loadFactor) {
        this(maxSize, loadFactor, false);
    }

    
Constructs a new, empty map with the specified max / initial capacity and
load factor.
Params:
maxSize –  the maximum size of the map
initialSize –  the initial size of the map
loadFactor –  the load factor
Throws:
IllegalArgumentException – if the maximum size is less than one
IllegalArgumentException – if the initial size is negative or larger than the maximum size
IllegalArgumentException – if the load factor is less than zero
Since:
4.1/**
     * Constructs a new, empty map with the specified max / initial capacity and
     * load factor.
     *
     * @param maxSize  the maximum size of the map
     * @param initialSize  the initial size of the map
     * @param loadFactor  the load factor
     * @throws IllegalArgumentException if the maximum size is less than one
     * @throws IllegalArgumentException if the initial size is negative or larger than the maximum size
     * @throws IllegalArgumentException if the load factor is less than zero
     * @since 4.1
     */
    public LRUMap(final int maxSize, final int initialSize, final float loadFactor) {
        this(maxSize, initialSize, loadFactor, false);
    }

    
Constructs a new, empty map with the specified max capacity and load factor.
Params:
maxSize –  the maximum size of the map
loadFactor –  the load factor
scanUntilRemovable –  scan until a removeable entry is found, default false
Throws:
IllegalArgumentException – if the maximum size is less than one
IllegalArgumentException – if the load factor is less than zero
Since:
3.1/**
     * Constructs a new, empty map with the specified max capacity and load factor.
     *
     * @param maxSize  the maximum size of the map
     * @param loadFactor  the load factor
     * @param scanUntilRemovable  scan until a removeable entry is found, default false
     * @throws IllegalArgumentException if the maximum size is less than one
     * @throws IllegalArgumentException if the load factor is less than zero
     * @since 3.1
     */
    public LRUMap(final int maxSize, final float loadFactor, final boolean scanUntilRemovable) {
        this(maxSize, maxSize, loadFactor, scanUntilRemovable);
    }

    
Constructs a new, empty map with the specified max / initial capacity and load factor.
Params:
maxSize –  the maximum size of the map
initialSize –  the initial size of the map
loadFactor –  the load factor
scanUntilRemovable –  scan until a removeable entry is found, default false
Throws:
IllegalArgumentException – if the maximum size is less than one
IllegalArgumentException – if the initial size is negative or larger than the maximum size
IllegalArgumentException – if the load factor is less than zero
Since:
4.1/**
     * Constructs a new, empty map with the specified max / initial capacity and load factor.
     *
     * @param maxSize  the maximum size of the map
     * @param initialSize  the initial size of the map
     * @param loadFactor  the load factor
     * @param scanUntilRemovable  scan until a removeable entry is found, default false
     * @throws IllegalArgumentException if the maximum size is less than one
     * @throws IllegalArgumentException if the initial size is negative or larger than the maximum size
     * @throws IllegalArgumentException if the load factor is less than zero
     * @since 4.1
     */
    public LRUMap(final int maxSize,
                  final int initialSize,
                  final float loadFactor,
                  final boolean scanUntilRemovable) {

        super(initialSize, loadFactor);
        if (maxSize < 1) {
            throw new IllegalArgumentException("LRUMap max size must be greater than 0");
        }
        if (initialSize > maxSize) {
            throw new IllegalArgumentException("LRUMap initial size must not be greather than max size");
        }
        this.maxSize = maxSize;
        this.scanUntilRemovable = scanUntilRemovable;
    }

    
Constructor copying elements from another map.

The maximum size is set from the map's size.
Params:
map –  the map to copy
Throws:
NullPointerException – if the map is null
IllegalArgumentException – if the map is empty/**
     * Constructor copying elements from another map.
     * <p>
     * The maximum size is set from the map's size.
     *
     * @param map  the map to copy
     * @throws NullPointerException if the map is null
     * @throws IllegalArgumentException if the map is empty
     */
    public LRUMap(final Map<? extends K, ? extends V> map) {
        this(map, false);
    }

    
Constructor copying elements from another map.
The maximum size is set from the map's size.
Params:
map –  the map to copy
scanUntilRemovable –  scan until a removeable entry is found, default false
Throws:
NullPointerException – if the map is null
IllegalArgumentException – if the map is empty
Since:
3.1/**
     * Constructor copying elements from another map.
     *
     * <p>The maximum size is set from the map's size.</p>
     *
     * @param map  the map to copy
     * @param scanUntilRemovable  scan until a removeable entry is found, default false
     * @throws NullPointerException if the map is null
     * @throws IllegalArgumentException if the map is empty
     * @since 3.1
     */
    public LRUMap(final Map<? extends K, ? extends V> map, final boolean scanUntilRemovable) {
        this(map.size(), DEFAULT_LOAD_FACTOR, scanUntilRemovable);
        putAll(map);
    }

    //-----------------------------------------------------------------------
    
Gets the value mapped to the key specified.

This operation changes the position of the key in the map to the
most recently used position (last).
Params:
key –  the key
Returns:
the mapped value, null if no match/**
     * Gets the value mapped to the key specified.
     * <p>
     * This operation changes the position of the key in the map to the
     * most recently used position (last).
     *
     * @param key  the key
     * @return the mapped value, null if no match
     */
    @Override
    public V get(final Object key) {
        return get(key, true);
    }

    
Gets the value mapped to the key specified.
 If updateToMRU is true, the position of the key in the map is changed to the most recently used position (last), otherwise the iteration order is not changed by this operation. 
Params:
key –  the key
updateToMRU –  whether the key shall be updated to the
  most recently used position
Returns:
the mapped value, null if no match
Since:
4.1/**
     * Gets the value mapped to the key specified.
     * <p>
     * If {@code updateToMRU} is {@code true}, the position of the key in the map
     * is changed to the most recently used position (last), otherwise the iteration
     * order is not changed by this operation.
     *
     * @param key  the key
     * @param updateToMRU  whether the key shall be updated to the
     *   most recently used position
     * @return the mapped value, null if no match
     * @since 4.1
     */
    public V get(final Object key, final boolean updateToMRU) {
        final LinkEntry<K, V> entry = getEntry(key);
        if (entry == null) {
            return null;
        }
        if (updateToMRU) {
            moveToMRU(entry);
        }
        return entry.getValue();
    }

    //-----------------------------------------------------------------------
    
Moves an entry to the MRU position at the end of the list.

This implementation moves the updated entry to the end of the list.
Params:
entry –  the entry to update/**
     * Moves an entry to the MRU position at the end of the list.
     * <p>
     * This implementation moves the updated entry to the end of the list.
     *
     * @param entry  the entry to update
     */
    protected void moveToMRU(final LinkEntry<K, V> entry) {
        if (entry.after != header) {
            modCount++;
            // remove
            if(entry.before == null) {
                throw new IllegalStateException("Entry.before is null." +
                    " This should not occur if your keys are immutable, and you have used synchronization properly.");
            }
            entry.before.after = entry.after;
            entry.after.before = entry.before;
            // add first
            entry.after = header;
            entry.before = header.before;
            header.before.after = entry;
            header.before = entry;
        } else if (entry == header) {
            throw new IllegalStateException("Can't move header to MRU" +
                    " This should not occur if your keys are immutable, and you have used synchronization properly.");
        }
    }

    
Updates an existing key-value mapping.
 This implementation moves the updated entry to the end of the list using moveToMRU(LinkEntry). 
Params:
entry –  the entry to update
newValue –  the new value to store/**
     * Updates an existing key-value mapping.
     * <p>
     * This implementation moves the updated entry to the end of the list
     * using {@link #moveToMRU(AbstractLinkedMap.LinkEntry)}.
     *
     * @param entry  the entry to update
     * @param newValue  the new value to store
     */
    @Override
    protected void updateEntry(final HashEntry<K, V> entry, final V newValue) {
        moveToMRU((LinkEntry<K, V>) entry);  // handles modCount
        entry.setValue(newValue);
    }

    
Adds a new key-value mapping into this map.
 This implementation checks the LRU size and determines whether to discard an entry or not using removeLRU(LinkEntry). 
 From Commons Collections 3.1 this method uses isFull() rather than accessing size and maxSize directly.
It also handles the scanUntilRemovable functionality.
Params:
hashIndex –  the index into the data array to store at
hashCode –  the hash code of the key to add
key –  the key to add
value –  the value to add/**
     * Adds a new key-value mapping into this map.
     * <p>
     * This implementation checks the LRU size and determines whether to
     * discard an entry or not using {@link #removeLRU(AbstractLinkedMap.LinkEntry)}.
     * <p>
     * From Commons Collections 3.1 this method uses {@link #isFull()} rather
     * than accessing <code>size</code> and <code>maxSize</code> directly.
     * It also handles the scanUntilRemovable functionality.
     *
     * @param hashIndex  the index into the data array to store at
     * @param hashCode  the hash code of the key to add
     * @param key  the key to add
     * @param value  the value to add
     */
    @Override
    protected void addMapping(final int hashIndex, final int hashCode, final K key, final V value) {
        if (isFull()) {
            LinkEntry<K, V> reuse = header.after;
            boolean removeLRUEntry = false;
            if (scanUntilRemovable) {
                while (reuse != header && reuse != null) {
                    if (removeLRU(reuse)) {
                        removeLRUEntry = true;
                        break;
                    }
                    reuse = reuse.after;
                }
                if (reuse == null) {
                    throw new IllegalStateException(
                        "Entry.after=null, header.after=" + header.after + " header.before=" + header.before +
                        " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                        " This should not occur if your keys are immutable, and you have used synchronization properly.");
                }
            } else {
                removeLRUEntry = removeLRU(reuse);
            }

            if (removeLRUEntry) {
                if (reuse == null) {
                    throw new IllegalStateException(
                        "reuse=null, header.after=" + header.after + " header.before=" + header.before +
                        " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                        " This should not occur if your keys are immutable, and you have used synchronization properly.");
            }
                reuseMapping(reuse, hashIndex, hashCode, key, value);
            } else {
                super.addMapping(hashIndex, hashCode, key, value);
            }
        } else {
            super.addMapping(hashIndex, hashCode, key, value);
        }
    }

    
Reuses an entry by removing it and moving it to a new place in the map.
 This method uses AbstractLinkedMap.removeEntry, AbstractHashedMap.reuseEntry and AbstractLinkedMap.addEntry. 
Params:
entry –  the entry to reuse
hashIndex –  the index into the data array to store at
hashCode –  the hash code of the key to add
key –  the key to add
value –  the value to add/**
     * Reuses an entry by removing it and moving it to a new place in the map.
     * <p>
     * This method uses {@link #removeEntry}, {@link #reuseEntry} and {@link #addEntry}.
     *
     * @param entry  the entry to reuse
     * @param hashIndex  the index into the data array to store at
     * @param hashCode  the hash code of the key to add
     * @param key  the key to add
     * @param value  the value to add
     */
    protected void reuseMapping(final LinkEntry<K, V> entry, final int hashIndex, final int hashCode,
                                final K key, final V value) {
        // find the entry before the entry specified in the hash table
        // remember that the parameters (except the first) refer to the new entry,
        // not the old one
        try {
            final int removeIndex = hashIndex(entry.hashCode, data.length);
            final HashEntry<K, V>[] tmp = data;  // may protect against some sync issues
            HashEntry<K, V> loop = tmp[removeIndex];
            HashEntry<K, V> previous = null;
            while (loop != entry && loop != null) {
                previous = loop;
                loop = loop.next;
            }
            if (loop == null) {
                throw new IllegalStateException(
                    "Entry.next=null, data[removeIndex]=" + data[removeIndex] + " previous=" + previous +
                    " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                    " This should not occur if your keys are immutable, and you have used synchronization properly.");
            }

            // reuse the entry
            modCount++;
            removeEntry(entry, removeIndex, previous);
            reuseEntry(entry, hashIndex, hashCode, key, value);
            addEntry(entry, hashIndex);
        } catch (final NullPointerException ex) {
            throw new IllegalStateException(
                    "NPE, entry=" + entry + " entryIsHeader=" + (entry==header) +
                    " key=" + key + " value=" + value + " size=" + size + " maxSize=" + maxSize +
                    " This should not occur if your keys are immutable, and you have used synchronization properly.");
        }
    }

    
Subclass method to control removal of the least recently used entry from the map.

This method exists for subclasses to override. A subclass may wish to
provide cleanup of resources when an entry is removed. For example:
protected boolean removeLRU(LinkEntry entry) {
  releaseResources(entry.getValue());  // release resources held by entry
  return true;  // actually delete entry
}


Alternatively, a subclass may choose to not remove the entry or selectively
keep certain LRU entries. For example:
protected boolean removeLRU(LinkEntry entry) {
  if (entry.getKey().toString().startsWith("System.")) {
    return false;  // entry not removed from LRUMap
  } else {
    return true;  // actually delete entry
  }
}

The effect of returning false is dependent on the scanUntilRemovable flag.
If the flag is true, the next LRU entry will be passed to this method and so on
until one returns false and is removed, or every entry in the map has been passed.
If the scanUntilRemovable flag is false, the map will exceed the maximum size.

NOTE: Commons Collections 3.0 passed the wrong entry to this method.
This is fixed in version 3.1 onwards.
Params:
entry –  the entry to be removed
Returns:
true/**
     * Subclass method to control removal of the least recently used entry from the map.
     * <p>
     * This method exists for subclasses to override. A subclass may wish to
     * provide cleanup of resources when an entry is removed. For example:
     * <pre>
     * protected boolean removeLRU(LinkEntry entry) {
     *   releaseResources(entry.getValue());  // release resources held by entry
     *   return true;  // actually delete entry
     * }
     * </pre>
     * <p>
     * Alternatively, a subclass may choose to not remove the entry or selectively
     * keep certain LRU entries. For example:
     * <pre>
     * protected boolean removeLRU(LinkEntry entry) {
     *   if (entry.getKey().toString().startsWith("System.")) {
     *     return false;  // entry not removed from LRUMap
     *   } else {
     *     return true;  // actually delete entry
     *   }
     * }
     * </pre>
     * The effect of returning false is dependent on the scanUntilRemovable flag.
     * If the flag is true, the next LRU entry will be passed to this method and so on
     * until one returns false and is removed, or every entry in the map has been passed.
     * If the scanUntilRemovable flag is false, the map will exceed the maximum size.
     * <p>
     * NOTE: Commons Collections 3.0 passed the wrong entry to this method.
     * This is fixed in version 3.1 onwards.
     *
     * @param entry  the entry to be removed
     * @return {@code true}
     */
    protected boolean removeLRU(final LinkEntry<K, V> entry) {
        return true;
    }

    //-----------------------------------------------------------------------
    
Returns true if this map is full and no new mappings can be added.
Returns:
true if the map is full/**
     * Returns true if this map is full and no new mappings can be added.
     *
     * @return <code>true</code> if the map is full
     */
    @Override
    public boolean isFull() {
        return size >= maxSize;
    }

    
Gets the maximum size of the map (the bound).
Returns:
the maximum number of elements the map can hold/**
     * Gets the maximum size of the map (the bound).
     *
     * @return the maximum number of elements the map can hold
     */
    @Override
    public int maxSize() {
        return maxSize;
    }

    
Whether this LRUMap will scan until a removable entry is found when the
map is full.
Returns:
true if this map scans
Since:
3.1/**
     * Whether this LRUMap will scan until a removable entry is found when the
     * map is full.
     *
     * @return true if this map scans
     * @since 3.1
     */
    public boolean isScanUntilRemovable() {
        return scanUntilRemovable;
    }

    //-----------------------------------------------------------------------
    
Clones the map without cloning the keys or values.
Returns:
a shallow clone/**
     * Clones the map without cloning the keys or values.
     *
     * @return a shallow clone
     */
    @Override
    public LRUMap<K, V> clone() {
        return (LRUMap<K, V>) super.clone();
    }

    
Write the map out using a custom routine.
Params:
out –  the output stream
Throws:
IOException – if an error occurs while writing to the stream/**
     * Write the map out using a custom routine.
     *
     * @param out  the output stream
     * @throws IOException if an error occurs while writing to the stream
     */
    private void writeObject(final ObjectOutputStream out) throws IOException {
        out.defaultWriteObject();
        doWriteObject(out);
    }

    
Read the map in using a custom routine.
Params:
in – the input stream
Throws:
IOException – if an error occurs while reading from the stream
ClassNotFoundException – if an object read from the stream can not be loaded/**
     * Read the map in using a custom routine.
     *
     * @param in the input stream
     * @throws IOException if an error occurs while reading from the stream
     * @throws ClassNotFoundException if an object read from the stream can not be loaded
     */
    private void readObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
        in.defaultReadObject();
        doReadObject(in);
    }

    
Writes the data necessary for put() to work in deserialization.
Params:
out –  the output stream
Throws:
IOException – if an error occurs while writing to the stream/**
     * Writes the data necessary for <code>put()</code> to work in deserialization.
     *
     * @param out  the output stream
     * @throws IOException if an error occurs while writing to the stream
     */
    @Override
    protected void doWriteObject(final ObjectOutputStream out) throws IOException {
        out.writeInt(maxSize);
        super.doWriteObject(out);
    }

    
Reads the data necessary for put() to work in the superclass.
Params:
in –  the input stream
Throws:
IOException – if an error occurs while reading from the stream
ClassNotFoundException – if an object read from the stream can not be loaded/**
     * Reads the data necessary for <code>put()</code> to work in the superclass.
     *
     * @param in  the input stream
     * @throws IOException if an error occurs while reading from the stream
     * @throws ClassNotFoundException if an object read from the stream can not be loaded
     */
    @Override
    protected void doReadObject(final ObjectInputStream in) throws IOException, ClassNotFoundException {
        maxSize = in.readInt();
        super.doReadObject(in);
    }

}