public class HashMap<K,V>
    extends AbstractMap<K,V>
    implements Map<K,V>, Cloneable, Serializable
{

public abstract class AbstractMap<K,V> implements Map<K,V> {
    /**
     * Sole constructor.  (For invocation by subclass constructors, typically
     * implicit.)
     */
    protected AbstractMap() {
    }

public interface Map<K,V> {
    // Query Operations

    /**
     * Returns the number of key-value mappings in this map.  If the
     * map contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
     * <tt>Integer.MAX_VALUE</tt>.
     *
     * @return the number of key-value mappings in this map
     */
    int size();

public class HashMap<K,V>
    extends AbstractMap<K,V>
    implements Map<K,V>, Cloneable, Serializable
{

    /**
     * The default initial capacity - MUST be a power of two.
     */
    static final int DEFAULT_INITIAL_CAPACITY = 16;

    /**
     * The maximum capacity, used if a higher value is implicitly specified
     * by either of the constructors with arguments.
     * MUST be a power of two <= 1<<30.
     */
    static final int MAXIMUM_CAPACITY = 1 << 30;

    /**
     * The load factor used when none specified in constructor.
     */
    static final float DEFAULT_LOAD_FACTOR = 0.75f;

    /**
     * The table, resized as necessary. Length MUST Always be a power of two.
     */
    transient Entry[] table;

    /**
     * The number of key-value mappings contained in this map.
     */
    transient int size;

    /**
     * The next size value at which to resize (capacity * load factor).
     * @serial
     */
    int threshold;

    /**
     * The load factor for the hash table.
     *
     * @serial
     */
    final float loadFactor;

    /**
     * The number of times this HashMap has been structurally modified
     * Structural modifications are those that change the number of mappings in
     * the HashMap or otherwise modify its internal structure (e.g.,
     * rehash).  This field is used to make iterators on Collection-views of
     * the HashMap fail-fast.  (See ConcurrentModificationException).
     */
    transient volatile int modCount;

    /**
     * Constructs an empty <tt>HashMap</tt> with the specified initial
     * capacity and load factor.
     *
     * @param  initialCapacity the initial capacity
     * @param  loadFactor      the load factor
     * @throws IllegalArgumentException if the initial capacity is negative
     *         or the load factor is nonpositive
     */
    public HashMap(int initialCapacity, float loadFactor) {
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal initial capacity: " +
                                               initialCapacity);
        if (initialCapacity > MAXIMUM_CAPACITY)
            initialCapacity = MAXIMUM_CAPACITY;
        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new IllegalArgumentException("Illegal load factor: " +
                                               loadFactor);

        // Find a power of 2 >= initialCapacity
        int capacity = 1;
        while (capacity < initialCapacity)
            capacity <<= 1;

        this.loadFactor = loadFactor;
        threshold = (int)(capacity * loadFactor);
        table = new Entry[capacity];
        init();
    }
 static class Entry<K,V> implements Map.Entry<K,V> {
        final K key;
        V value;
        Entry<K,V> next;
        final int hash;

        /**
         * Creates new entry.
         */
        Entry(int h, K k, V v, Entry<K,V> n) {
            value = v;
            next = n;
            key = k;
            hash = h;
        }

    public V put(K key, V value) {
        if (key == null)
            return putForNullKey(value);
        int hash = hash(key.hashCode());
        int i = indexFor(hash, table.length);
        for (Entry<K,V> e = table[i]; e != null; e = e.next) {
            Object k;
            if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
                V oldValue = e.value;
                e.value = value;
                e.recordAccess(this);
                return oldValue;
            }
        }

        modCount++;
        addEntry(hash, key, value, i);
        return null;
    }

    void addEntry(int hash, K key, V value, int bucketIndex) {
    Entry<K,V> e = table[bucketIndex];
        table[bucketIndex] = new Entry<K,V>(hash, key, value, e); // 在链表头加上此Entry
        if (size++ >= threshold)
            resize(2 * table.length);
    }

    void resize(int newCapacity) {
        Entry[] oldTable = table;
        int oldCapacity = oldTable.length;
        if (oldCapacity == MAXIMUM_CAPACITY) {
            threshold = Integer.MAX_VALUE;
            return;
        }

        Entry[] newTable = new Entry[newCapacity];
        transfer(newTable);
        table = newTable;
        threshold = (int)(newCapacity * loadFactor);
    }

public class LinkedHashMap<K,V>
    extends HashMap<K,V>
    implements Map<K,V>
{

    private static final long serialVersionUID = 3801124242820219131L;

    /**
     * The head of the doubly linked list.
     */
    private transient Entry<K,V> header; // 较HashMap多维护的一条双向链表

    /**
     * This override alters behavior of superclass put method. It causes newly
     * allocated entry to get inserted at the end of the linked list and
     * removes the eldest entry if appropriate.
     */
    void addEntry(int hash, K key, V value, int bucketIndex) {
        createEntry(hash, key, value, bucketIndex);

        // Remove eldest entry if instructed, else grow capacity if appropriate
        Entry<K,V> eldest = header.after;
        if (removeEldestEntry(eldest)) {
            removeEntryForKey(eldest.key);
        } else {
            if (size >= threshold)
                resize(2 * table.length);
        }
    }

public class WeakHashMap<K,V>
    extends AbstractMap<K,V>
    implements Map<K,V> {

    /**
     * The default initial capacity -- MUST be a power of two.
     */
    private static final int DEFAULT_INITIAL_CAPACITY = 16;

    /**
     * The maximum capacity, used if a higher value is implicitly specified
     * by either of the constructors with arguments.
     * MUST be a power of two <= 1<<30.
     */
    private static final int MAXIMUM_CAPACITY = 1 << 30;

    /**
     * The load fast used when none specified in constructor.
     */
    private static final float DEFAULT_LOAD_FACTOR = 0.75f;

    /**
     * The table, resized as necessary. Length MUST Always be a power of two.
     */
    private Entry[] table;

    /**
     * The number of key-value mappings contained in this weak hash map.
     */
    private int size;

    /**
     * The next size value at which to resize (capacity * load factor).
     */
    private int threshold;

    /**
     * The load factor for the hash table.
     */
    private final float loadFactor;

    /**
     * Reference queue for cleared WeakEntries
     */
    private final ReferenceQueue<K> queue = new ReferenceQueue<K>(); // 这个是重点，引用队列

 /**
     * The entries in this hash table extend WeakReference, using its main ref
     * field as the key.
     */
    private static class Entry<K,V> extends WeakReference<K> implements Map.Entry<K,V> {
        private V value;
        private final int hash;
        private Entry<K,V> next;

        /**
         * Creates new entry.
         */
        Entry(K key, V value,
          ReferenceQueue<K> queue,
              int hash, Entry<K,V> next) {
            super(key, queue);
            this.value =http://www.mamicode.com/ value;
            this.hash  = hash;
            this.next  = next;
        }

  /**
     * Expunges stale entries from the table.
     */
    private void expungeStaleEntries() {
    Entry<K,V> e;
        while ( (e = (Entry<K,V>) queue.poll()) != null) {
            int h = e.hash;
            int i = indexFor(h, table.length);

            Entry<K,V> prev = table[i];
            Entry<K,V> p = prev;
            while (p != null) {
                Entry<K,V> next = p.next;
                if (p == e) {
                    if (prev == e)
                        table[i] = next;
                    else
                        prev.next = next;
                    e.next = null;  // Help GC
                    e.value = http://www.mamicode.com/null; //  "   "
                    size--;
                    break;
                }
                prev = p;
                p = next;
            }
        }
    }

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

    /**
     * The hash table data.
     */
    private transient Entry[] table;

    /**
     * The total number of entries in the hash table.
     */
    private transient int count;

    /**
     * The table is rehashed when its size exceeds this threshold.  (The
     * value of this field is (int)(capacity * loadFactor).)
     *
     * @serial
     */
    private int threshold;

    /**
     * The load factor for the hashtable.
     *
     * @serial
     */
    private float loadFactor;

    /**
     * The number of times this Hashtable has been structurally modified
     * Structural modifications are those that change the number of entries in
     * the Hashtable or otherwise modify its internal structure (e.g.,
     * rehash).  This field is used to make iterators on Collection-views of
     * the Hashtable fail-fast.  (See ConcurrentModificationException).
     */
    private transient int modCount = 0;

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 1421746759512286392L;

    /**
     * Constructs a new, empty hashtable with the specified initial
     * capacity and the specified load factor.
     *
     * @param      initialCapacity   the initial capacity of the hashtable.
     * @param      loadFactor        the load factor of the hashtable.
     * @exception  IllegalArgumentException  if the initial capacity is less
     *             than zero, or if the load factor is nonpositive.
     */
    public Hashtable(int initialCapacity, float loadFactor) {
    if (initialCapacity < 0)
        throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new IllegalArgumentException("Illegal Load: "+loadFactor);

        if (initialCapacity==0)
            initialCapacity = 1;
    this.loadFactor = loadFactor;
    table = new Entry[initialCapacity];
    threshold = (int)(initialCapacity * loadFactor);
    }

    /**
     * Returns the number of keys in this hashtable.
     *
     * @return  the number of keys in this hashtable.
     */
    public synchronized int size() {
    return count;
    }

 public synchronized V put(K key, V value) {
    // Make sure the value is not null
    if (value =http://www.mamicode.com/= null) {
        throw new NullPointerException();
    }

    // Makes sure the key is not already in the hashtable.
    Entry tab[] = table;
    int hash = key.hashCode();
    int index = (hash & 0x7FFFFFFF) % tab.length;
    for (Entry<K,V> e = tab[index] ; e != null ; e = e.next) {
        if ((e.hash == hash) && e.key.equals(key)) {
        V old = e.value;
        e.value = value;
        return old;
        }
    }

    modCount++;
    if (count >= threshold) {
        // Rehash the table if the threshold is exceeded
        rehash(); ///////////////////////////////////////////////////////////////////////////////////////

            tab = table;
            index = (hash & 0x7FFFFFFF) % tab.length;
    }

 private void resize(int newCapacity) {
        // assert (newCapacity & -newCapacity) == newCapacity; // power of 2
        int newLength = newCapacity * 2;

    Object[] oldTable = table;
        int oldLength = oldTable.length;
        if (oldLength == 2*MAXIMUM_CAPACITY) { // can‘t expand any further
            if (threshold == MAXIMUM_CAPACITY-1)
                throw new IllegalStateException("Capacity exhausted.");
            threshold = MAXIMUM_CAPACITY-1;  // Gigantic map!
            return;
        }
        if (oldLength >= newLength)
            return;

    Object[] newTable = new Object[newLength];
        threshold = newLength / 3;

        for (int j = 0; j < oldLength; j += 2) {
            Object key = oldTable[j];
            if (key != null) {
                Object value = oldTable[j+1];
                oldTable[j] = null;
                oldTable[j+1] = null;
                int i = hash(key, newLength); ////////////////////这里重哈希了/////////////////////////
                while (newTable[i] != null)
                    i = nextKeyIndex(i, newLength);
                newTable[i] = key;
                newTable[i + 1] = value;
            }
        }
        table = newTable;
    }

 static final class Entry<K,V> implements Map.Entry<K,V> {
    K key;
        V value;
        Entry<K,V> left = null;
        Entry<K,V> right = null;
        Entry<K,V> parent;
        boolean color = BLACK;

        /**
         * Make a new cell with given key, value, and parent, and with
         * <tt>null</tt> child links, and BLACK color.
         */
        Entry(K key, V value, Entry<K,V> parent) {
            this.key = key;
            this.value =http://www.mamicode.com/ value;
            this.parent = parent;
        }