java/util/Hashtable.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 java.util;

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

import org.apache.harmony.luni.internal.nls.Messages;

/**
 * Hashtable associates keys with values. Both keys and values cannot be null.
 * The size of the Hashtable is the number of key/value pairs it contains. The
 * capacity is the number of key/value pairs the Hashtable can hold. The load
 * factor is a float value which determines how full the Hashtable gets before
 * expanding the capacity. If the load factor of the Hashtable is exceeded, the
 * capacity is doubled.
 *
 * @see Enumeration
 * @see java.io.Serializable
 * @see java.lang.Object#equals
 * @see java.lang.Object#hashCode
 * @since Android 1.0
 */

public class Hashtable<K, V> extends Dictionary<K, V> implements Map<K, V>,
        Cloneable, Serializable {

    private static final long serialVersionUID = 1421746759512286392L;

    transient int elementCount;

    transient Entry<K, V>[] elementData;

    private float loadFactor;

    private int threshold;

    transient int firstSlot;

    transient int lastSlot = -1;

    transient int modCount;

    private static final Enumeration<?> EMPTY_ENUMERATION = new Enumeration<Object>() {
        public boolean hasMoreElements() {
            return false;
        }

        public Object nextElement() {
            throw new NoSuchElementException();
        }
    };

    private static <K, V> Entry<K, V> newEntry(K key, V value, int hash) {
        return new Entry<K, V>(key, value);
    }

    private static class Entry<K, V> extends MapEntry<K, V> {
        Entry<K, V> next;

        final int hashcode;

        Entry(K theKey, V theValue) {
            super(theKey, theValue);
            hashcode = theKey.hashCode();
        }

        @Override
        @SuppressWarnings("unchecked")
        public Object clone() {
            Entry<K, V> entry = (Entry<K, V>) super.clone();
            if (next != null) {
                entry.next = (Entry<K, V>) next.clone();
            }
            return entry;
        }

        @Override
        public V setValue(V object) {
            if (object == null) {
                throw new NullPointerException();
            }
            V result = value;
            value = object;
            return result;
        }

        public int getKeyHash() {
            return key.hashCode();
        }

        public boolean equalsKey(Object aKey, int hash) {
            // BEGIN android-changed
            // The VM can inline String.equals
            return hashcode == aKey.hashCode()
               && (key instanceof String
                   ? ((String) key).equals(aKey) : key.equals(aKey));
            // END android-changed
        }

        @Override
        public String toString() {
            return key + "=" + value; //$NON-NLS-1$
        }
    }

    private final class HashIterator<E> implements Iterator<E> {
        private int position, expectedModCount;

        private final MapEntry.Type<E, K, V> type;

        private Entry<K, V> lastEntry;

        private int lastPosition;

        private boolean canRemove = false;

        HashIterator(MapEntry.Type<E, K, V> value) {
            type = value;
            position = lastSlot;
            expectedModCount = modCount;
        }

        public boolean hasNext() {
            if (lastEntry != null && lastEntry.next != null) {
                return true;
            }
            while (position >= firstSlot) {
                if (elementData[position] == null) {
                    position--;
                } else {
                    return true;
                }
            }
            return false;
        }

        public E next() {
            if (expectedModCount == modCount) {
                if (lastEntry != null) {
                    lastEntry = lastEntry.next;
                }
                if (lastEntry == null) {
                    while (position >= firstSlot
                            && (lastEntry = elementData[position]) == null) {
                        position--;
                    }
                    if (lastEntry != null) {
                        lastPosition = position;
                        // decrement the position so we don't find the same slot
                        // next time
                        position--;
                    }
                }
                if (lastEntry != null) {
                    canRemove = true;
                    return type.get(lastEntry);
                }
                throw new NoSuchElementException();
            }
            throw new ConcurrentModificationException();
        }

        public void remove() {
            if (expectedModCount == modCount) {
                if (canRemove) {
                    canRemove = false;
                    synchronized (Hashtable.this) {
                        boolean removed = false;
                        Entry<K, V> entry = elementData[lastPosition];
                        if (entry == lastEntry) {
                            elementData[lastPosition] = entry.next;
                            removed = true;
                        } else {
                            while (entry != null && entry.next != lastEntry) {
                                entry = entry.next;
                            }
                            if (entry != null) {
                                entry.next = lastEntry.next;
                                removed = true;
                            }
                        }
                        if (removed) {
                            modCount++;
                            elementCount--;
                            expectedModCount++;
                            return;
                        }
                        // the entry must have been (re)moved outside of the
                        // iterator
                        // but this condition wasn't caught by the modCount
                        // check
                        // throw ConcurrentModificationException() outside of
                        // synchronized block
                    }
                } else {
                    throw new IllegalStateException();
                }
            }
            throw new ConcurrentModificationException();
        }
    }

    private final class HashEnumerator<E> implements Enumeration<E> {
        boolean key;

        int start;

        Entry<K, V> entry;

        HashEnumerator(boolean isKey) {
            key = isKey;
            start = lastSlot + 1;
        }

        public boolean hasMoreElements() {
            if (entry != null) {
                return true;
            }
            while (--start >= firstSlot) {
                if (elementData[start] != null) {
                    entry = elementData[start];
                    return true;
                }
            }
            return false;
        }

        @SuppressWarnings("unchecked")
        public E nextElement() {
            if (hasMoreElements()) {
                Object result = key ? entry.key : entry.value;
                entry = entry.next;
                return (E) result;
            }
            throw new NoSuchElementException();
        }
    }

    /**
     * Constructs a new {@code Hashtable} using the default capacity and load
     * factor.
     *
     * @since Android 1.0
     */
    public Hashtable() {
        this(11);
    }

    /**
     * Constructs a new {@code Hashtable} using the specified capacity and the
     * default load factor.
     *
     * @param capacity
     *            the initial capacity.
     * @since Android 1.0
     */
    public Hashtable(int capacity) {
        if (capacity >= 0) {
            elementCount = 0;
            elementData = newElementArray(capacity == 0 ? 1 : capacity);
            firstSlot = elementData.length;
            loadFactor = 0.75f;
            computeMaxSize();
        } else {
            throw new IllegalArgumentException();
        }
    }

    /**
     * Constructs a new {@code Hashtable} using the specified capacity and load
     * factor.
     *
     * @param capacity
     *            the initial capacity.
     * @param loadFactor
     *            the initial load factor.
     * @since Android 1.0
     */
    public Hashtable(int capacity, float loadFactor) {
        if (capacity >= 0 && loadFactor > 0) {
            elementCount = 0;
            firstSlot = capacity;
            elementData = newElementArray(capacity == 0 ? 1 : capacity);
            this.loadFactor = loadFactor;
            computeMaxSize();
        } else {
            throw new IllegalArgumentException();
        }
    }

    /**
     * Constructs a new instance of {@code Hashtable} containing the mappings
     * from the specified map.
     *
     * @param map
     *            the mappings to add.
     * @since Android 1.0
     */
    public Hashtable(Map<? extends K, ? extends V> map) {
        this(map.size() < 6 ? 11 : (map.size() * 4 / 3) + 11);
        putAll(map);
    }

    @SuppressWarnings("unchecked")
    private Entry<K, V>[] newElementArray(int size) {
        return new Entry[size];
    }

    /**
     * Removes all key/value pairs from this {@code Hashtable}, leaving the
     * size zero and the capacity unchanged.
     *
     * @see #isEmpty
     * @see #size
     * @since Android 1.0
     */
    public synchronized void clear() {
        elementCount = 0;
        Arrays.fill(elementData, null);
        modCount++;
    }

    /**
     * Returns a new {@code Hashtable} with the same key/value pairs, capacity
     * and load factor.
     *
     * @return a shallow copy of this {@code Hashtable}.
     * @see java.lang.Cloneable
     * @since Android 1.0
     */
    @Override
    @SuppressWarnings("unchecked")
    public synchronized Object clone() {
        try {
            Hashtable<K, V> hashtable = (Hashtable<K, V>) super.clone();
            hashtable.elementData = elementData.clone();
            Entry<K, V> entry;
            for (int i = elementData.length; --i >= 0;) {
                if ((entry = elementData[i]) != null) {
                    hashtable.elementData[i] = (Entry<K, V>) entry.clone();
                }
            }
            return hashtable;
        } catch (CloneNotSupportedException e) {
            return null;
        }
    }

    private void computeMaxSize() {
        threshold = (int) (elementData.length * loadFactor);
    }

    /**
     * Returns true if this {@code Hashtable} contains the specified object as
     * the value of at least one of the key/value pairs.
     *
     * @param value
     *            the object to look for as a value in this {@code Hashtable}.
     * @return {@code true} if object is a value in this {@code Hashtable},
     *         {@code false} otherwise.
     * @see #containsKey
     * @see java.lang.Object#equals
     * @since Android 1.0
     */
    public synchronized boolean contains(Object value) {
        if (value == null) {
            throw new NullPointerException();
        }

        for (int i = elementData.length; --i >= 0;) {
            Entry<K, V> entry = elementData[i];
            while (entry != null) {
                if (value.equals(entry.value)) {
                    return true;
                }
                entry = entry.next;
            }
        }
        return false;
    }

    /**
     * Returns true if this {@code Hashtable} contains the specified object as a
     * key of one of the key/value pairs.
     *
     * @param key
     *            the object to look for as a key in this {@code Hashtable}.
     * @return {@code true} if object is a key in this {@code Hashtable},
     *         {@code false} otherwise.
     * @see #contains
     * @see java.lang.Object#equals
     * @since Android 1.0
     */
    public synchronized boolean containsKey(Object key) {
        return getEntry(key) != null;
    }

    /**
     * Searches this {@code Hashtable} for the specified value.
     *
     * @param value
     *            the object to search for.
     * @return {@code true} if {@code value} is a value of this
     *         {@code Hashtable}, {@code false} otherwise.
     * @since Android 1.0
     */
    public boolean containsValue(Object value) {
        return contains(value);
    }

    /**
     * Returns an enumeration on the values of this {@code Hashtable}. The
     * results of the Enumeration may be affected if the contents of this
     * {@code Hashtable} are modified.
     *
     * @return an enumeration of the values of this {@code Hashtable}.
     * @see #keys
     * @see #size
     * @see Enumeration
     * @since Android 1.0
     */
    @Override
    @SuppressWarnings("unchecked")
    public synchronized Enumeration<V> elements() {
        if (elementCount == 0) {
            return (Enumeration<V>) EMPTY_ENUMERATION;
        }
        return new HashEnumerator<V>(false);
    }

    /**
     * Returns a set of the mappings contained in this {@code Hashtable}. Each
     * element in the set is a {@link Map.Entry}. The set is backed by this
     * {@code Hashtable} so changes to one are reflected by the other. The set
     * does not support adding.
     *
     * @return a set of the mappings.
     * @since Android 1.0
     */
    public Set<Map.Entry<K, V>> entrySet() {
        return new Collections.SynchronizedSet<Map.Entry<K, V>>(
                new AbstractSet<Map.Entry<K, V>>() {
                    @Override
                    public int size() {
                        synchronized (Hashtable.this) {
                            return elementCount;
                        }
                    }

                    @Override
                    public void clear() {
                        Hashtable.this.clear();
                    }

                    @Override
                    @SuppressWarnings("unchecked")
                    public boolean remove(Object object) {
                        synchronized (Hashtable.this) {
                            if (contains(object)) {
                                Hashtable.this
                                        .remove(((Map.Entry<K, V>) object)
                                                .getKey());
                                return true;
                            }
                            return false;
                        }
                    }

                    @Override
                    @SuppressWarnings("unchecked")
                    public boolean contains(Object object) {
                        synchronized (Hashtable.this) {
                            Entry<K, V> entry = getEntry(((Map.Entry<K, V>) object)
                                    .getKey());
                            return object.equals(entry);
                        }
                    }

                    @Override
                    public Iterator<Map.Entry<K, V>> iterator() {
                        return new HashIterator<Map.Entry<K, V>>(
                                new MapEntry.Type<Map.Entry<K, V>, K, V>() {
                                    public Map.Entry<K, V> get(
                                            MapEntry<K, V> entry) {
                                        return entry;
                                    }
                                });
                    }
                }, this);
    }

    /**
     * Compares this {@code Hashtable} with the specified object and indicates
     * if they are equal. In order to be equal, {@code object} must be an
     * instance of Map and contain the same key/value pairs.
     *
     * @param object
     *            the object to compare with this object.
     * @return {@code true} if the specified object is equal to this Map,
     *         {@code false} otherwise.
     * @see #hashCode
     * @since Android 1.0
     */
    @Override
    public synchronized boolean equals(Object object) {
        if (this == object) {
            return true;
        }
        if (object instanceof Map) {
            Map<?, ?> map = (Map<?, ?>) object;
            if (size() != map.size()) {
                return false;
            }

            Set<Map.Entry<K, V>> entries = entrySet();
            for (Map.Entry<?, ?> e : map.entrySet()) {
                if (!entries.contains(e)) {
                    return false;
                }
            }
            return true;
        }
        return false;
    }

    /**
     * Returns the value associated with the specified key in this
     * {@code Hashtable}.
     *
     * @param key
     *            the key of the value returned.
     * @return the value associated with the specified key, or {@code null} if
     *         the specified key does not exist.
     * @see #put
     * @since Android 1.0
     */
    @Override
    public synchronized V get(Object key) {
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % elementData.length;
        Entry<K, V> entry = elementData[index];
        while (entry != null) {
            if (entry.equalsKey(key, hash)) {
                return entry.value;
            }
            entry = entry.next;
        }
        return null;
    }

    Entry<K, V> getEntry(Object key) {
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % elementData.length;
        Entry<K, V> entry = elementData[index];
        while (entry != null) {
            if (entry.equalsKey(key, hash)) {
                return entry;
            }
            entry = entry.next;
        }
        return null;
    }

    @Override
    public synchronized int hashCode() {
        int result = 0;
        Iterator<Map.Entry<K, V>> it = entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry<K, V> entry = it.next();
            Object key = entry.getKey();
            Object value = entry.getValue();
            int hash = (key != this ? key.hashCode() : 0)
                    ^ (value != this ? (value != null ? value.hashCode() : 0)
                            : 0);
            result += hash;
        }
        return result;
    }

    /**
     * Returns true if this {@code Hashtable} has no key/value pairs.
     *
     * @return {@code true} if this {@code Hashtable} has no key/value pairs,
     *         {@code false} otherwise.
     * @see #size
     * @since Android 1.0
     */
    @Override
    public synchronized boolean isEmpty() {
        return elementCount == 0;
    }

    /**
     * Returns an enumeration on the keys of this {@code Hashtable} instance.
     * The results of the enumeration may be affected if the contents of this
     * {@code Hashtable} are modified.
     *
     * @return an enumeration of the keys of this {@code Hashtable}.
     * @see #elements
     * @see #size
     * @see Enumeration
     * @since Android 1.0
     */
    @Override
    @SuppressWarnings("unchecked")
    public synchronized Enumeration<K> keys() {
        if (elementCount == 0) {
            return (Enumeration<K>) EMPTY_ENUMERATION;
        }
        return new HashEnumerator<K>(true);
    }

    /**
     * Returns a set of the keys contained in this {@code Hashtable}. The set
     * is backed by this {@code Hashtable} so changes to one are reflected by
     * the other. The set does not support adding.
     *
     * @return a set of the keys.
     * @since Android 1.0
     */
    public Set<K> keySet() {
        return new Collections.SynchronizedSet<K>(new AbstractSet<K>() {
            @Override
            public boolean contains(Object object) {
                synchronized (Hashtable.this) {
                    return containsKey(object);
                }
            }

            @Override
            public int size() {
                synchronized (Hashtable.this) {
                    return elementCount;
                }
            }

            @Override
            public void clear() {
                Hashtable.this.clear();
            }

            @Override
            public boolean remove(Object key) {
                synchronized (Hashtable.this) {
                    if (containsKey(key)) {
                        Hashtable.this.remove(key);
                        return true;
                    }
                    return false;
                }
            }

            @Override
            public Iterator<K> iterator() {
                return new HashIterator<K>(new MapEntry.Type<K, K, V>() {
                    public K get(MapEntry<K, V> entry) {
                        return entry.key;
                    }
                });
            }
        }, this);
    }

    /**
     * Associate the specified value with the specified key in this
     * {@code Hashtable}. If the key already exists, the old value is replaced.
     * The key and value cannot be null.
     *
     * @param key
     *            the key to add.
     * @param value
     *            the value to add.
     * @return the old value associated with the specified key, or {@code null}
     *         if the key did not exist.
     * @see #elements
     * @see #get
     * @see #keys
     * @see java.lang.Object#equals
     * @since Android 1.0
     */
    @Override
    public synchronized V put(K key, V value) {
        if (key != null && value != null) {
            int hash = key.hashCode();
            int index = (hash & 0x7FFFFFFF) % elementData.length;
            Entry<K, V> entry = elementData[index];
            while (entry != null && !entry.equalsKey(key, hash)) {
                entry = entry.next;
            }
            if (entry == null) {
                modCount++;
                if (++elementCount > threshold) {
                    rehash();
                    index = (hash & 0x7FFFFFFF) % elementData.length;
                }
                if (index < firstSlot) {
                    firstSlot = index;
                }
                if (index > lastSlot) {
                    lastSlot = index;
                }
                entry = newEntry(key, value, hash);
                entry.next = elementData[index];
                elementData[index] = entry;
                return null;
            }
            V result = entry.value;
            entry.value = value;
            return result;
        }
        throw new NullPointerException();
    }

    /**
     * Copies every mapping to this {@code Hashtable} from the specified map.
     *
     * @param map
     *            the map to copy mappings from.
     * @since Android 1.0
     */
    public synchronized void putAll(Map<? extends K, ? extends V> map) {
        for (Map.Entry<? extends K, ? extends V> entry : map.entrySet()) {
            put(entry.getKey(), entry.getValue());
        }
    }

    /**
     * Increases the capacity of this {@code Hashtable}. This method is called
     * when the size of this {@code Hashtable} exceeds the load factor.
     *
     * @since Android 1.0
     */
    protected void rehash() {
        int length = (elementData.length << 1) + 1;
        if (length == 0) {
            length = 1;
        }
        int newFirst = length;
        int newLast = -1;
        Entry<K, V>[] newData = newElementArray(length);
        for (int i = lastSlot + 1; --i >= firstSlot;) {
            Entry<K, V> entry = elementData[i];
            while (entry != null) {
                int index = (entry.getKeyHash() & 0x7FFFFFFF) % length;
                if (index < newFirst) {
                    newFirst = index;
                }
                if (index > newLast) {
                    newLast = index;
                }
                Entry<K, V> next = entry.next;
                entry.next = newData[index];
                newData[index] = entry;
                entry = next;
            }
        }
        firstSlot = newFirst;
        lastSlot = newLast;
        elementData = newData;
        computeMaxSize();
    }

    /**
     * Removes the key/value pair with the specified key from this
     * {@code Hashtable}.
     *
     * @param key
     *            the key to remove.
     * @return the value associated with the specified key, or {@code null} if
     *         the specified key did not exist.
     * @see #get
     * @see #put
     * @since Android 1.0
     */
    @Override
    public synchronized V remove(Object key) {
        int hash = key.hashCode();
        int index = (hash & 0x7FFFFFFF) % elementData.length;
        Entry<K, V> last = null;
        Entry<K, V> entry = elementData[index];
        while (entry != null && !entry.equalsKey(key, hash)) {
            last = entry;
            entry = entry.next;
        }
        if (entry != null) {
            modCount++;
            if (last == null) {
                elementData[index] = entry.next;
            } else {
                last.next = entry.next;
            }
            elementCount--;
            V result = entry.value;
            entry.value = null;
            return result;
        }
        return null;
    }

    /**
     * Returns the number of key/value pairs in this {@code Hashtable}.
     *
     * @return the number of key/value pairs in this {@code Hashtable}.
     * @see #elements
     * @see #keys
     * @since Android 1.0
     */
    @Override
    public synchronized int size() {
        return elementCount;
    }

    /**
     * Returns the string representation of this {@code Hashtable}.
     *
     * @return the string representation of this {@code Hashtable}.
     * @since Android 1.0
     */
    @Override
    public synchronized String toString() {
        if (isEmpty()) {
            return "{}"; //$NON-NLS-1$
        }

        StringBuilder buffer = new StringBuilder(size() * 28);
        buffer.append('{');
        for (int i = lastSlot; i >= firstSlot; i--) {
            Entry<K, V> entry = elementData[i];
            while (entry != null) {
                if (entry.key != this) {
                    buffer.append(entry.key);
                } else {
                    // luni.04=this Map
                    buffer.append("(" + Messages.getString("luni.04") + ")"); //$NON-NLS-1$//$NON-NLS-2$//$NON-NLS-3$
                }
                buffer.append('=');
                if (entry.value != this) {
                    buffer.append(entry.value);
                } else {
                    // luni.04=this Map
                    buffer.append("(" + Messages.getString("luni.04") + ")"); //$NON-NLS-1$//$NON-NLS-2$//$NON-NLS-3$
                }
                buffer.append(", "); //$NON-NLS-1$
                entry = entry.next;
            }
        }
        // Remove the last ", "
        if (elementCount > 0) {
            buffer.setLength(buffer.length() - 2);
        }
        buffer.append('}');
        return buffer.toString();
    }

    /**
     * Returns a collection of the values contained in this {@code Hashtable}.
     * The collection is backed by this {@code Hashtable} so changes to one are
     * reflected by the other. The collection does not support adding.
     *
     * @return a collection of the values.
     * @since Android 1.0
     */
    public Collection<V> values() {
        return new Collections.SynchronizedCollection<V>(
                new AbstractCollection<V>() {
                    @Override
                    public boolean contains(Object object) {
                        synchronized (Hashtable.this) {
                            return Hashtable.this.contains(object);
                        }
                    }

                    @Override
                    public int size() {
                        synchronized (Hashtable.this) {
                            return elementCount;
                        }
                    }

                    @Override
                    public void clear() {
                        Hashtable.this.clear();
                    }

                    @Override
                    public Iterator<V> iterator() {
                        return new HashIterator<V>(
                                new MapEntry.Type<V, K, V>() {
                                    public V get(MapEntry<K, V> entry) {
                                        return entry.value;
                                    }
                                });
                    }
                }, this);
    }

    private synchronized void writeObject(ObjectOutputStream stream)
            throws IOException {
        stream.defaultWriteObject();
        stream.writeInt(elementData.length);
        stream.writeInt(elementCount);
        for (int i = elementData.length; --i >= 0;) {
            Entry<K, V> entry = elementData[i];
            while (entry != null) {
                stream.writeObject(entry.key);
                stream.writeObject(entry.value);
                entry = entry.next;
            }
        }
    }

    @SuppressWarnings("unchecked")
    private void readObject(ObjectInputStream stream) throws IOException,
            ClassNotFoundException {
        stream.defaultReadObject();
        int length = stream.readInt();
        elementData = newElementArray(length);
        elementCount = stream.readInt();
        for (int i = elementCount; --i >= 0;) {
            Object key = stream.readObject();
            int hash = key.hashCode();
            int index = (hash & 0x7FFFFFFF) % length;
            if (index < firstSlot) {
                firstSlot = index;
            }
            if (index > lastSlot) {
                lastSlot = index;
            }
            Entry<K, V> entry = newEntry((K) key, (V) stream.readObject(), hash);
            entry.next = elementData[index];
            elementData[index] = entry;
        }
    }
}