hashtable.java

java源代码 请看看啊 提点宝贵的意见

     * Compares the specified Object with this Map for equality,
     * as per the definition in the Map interface.
     *
     * @param  o object to be compared for equality with this Hashtable
     * @return true if the specified Object is equal to this Map.
     * @see Map#equals(Object)
     * @since 1.2
     */
    public synchronized boolean equals(Object o) {
	if (o == this)
	    return true;

	if (!(o instanceof Map))
	    return false;
	Map t = (Map) o;
	if (t.size() != size())
	    return false;

        try {
            Iterator i = entrySet().iterator();
            while (i.hasNext()) {
                Map.Entry e = (Map.Entry) i.next();
                Object key = e.getKey();
                Object value = e.getValue();
                if (value == null) {
                    if (!(t.get(key)==null && t.containsKey(key)))
                        return false;
                } else {
                    if (!value.equals(t.get(key)))
                        return false;
                }
            }
        } catch(ClassCastException unused)   {
            return false;
        } catch(NullPointerException unused) {
            return false;
        }

	return true;
    }

    /**
     * Returns the hash code value for this Map as per the definition in the
     * Map interface.
     *
     * @see Map#hashCode()
     * @since 1.2
     */
    public synchronized int hashCode() {
        /*
         * This code detects the recursion caused by computing the hash code
         * of a self-referential hash table and prevents the stack overflow
         * that would otherwise result.  This allows certain 1.1-era
         * applets with self-referential hash tables to work.  This code
         * abuses the loadFactor field to do double-duty as a hashCode
         * in progress flag, so as not to worsen the space performance.
         * A negative load factor indicates that hash code computation is
         * in progress.
         */
        int h = 0;
        if (count == 0 || loadFactor < 0)
            return h;  // Returns zero

        loadFactor = -loadFactor;  // Mark hashCode computation in progress
        Entry tab[] = table;
        for (int i = 0; i < tab.length; i++)
            for (Entry e = tab[i]; e != null; e = e.next)
                h += e.key.hashCode() ^ e.value.hashCode();
        loadFactor = -loadFactor;  // Mark hashCode computation complete

	return h;
    }

    /**
     * Save the state of the Hashtable to a stream (i.e., serialize it).
     *
     * @serialData The <i>capacity</i> of the Hashtable (the length of the
     *		   bucket array) is emitted (int), followed  by the
     *		   <i>size</i> of the Hashtable (the number of key-value
     *		   mappings), followed by the key (Object) and value (Object)
     *		   for each key-value mapping represented by the Hashtable
     *		   The key-value mappings are emitted in no particular order.
     */
    private synchronized void writeObject(java.io.ObjectOutputStream s)
        throws IOException
    {
	// Write out the length, threshold, loadfactor
	s.defaultWriteObject();

	// Write out length, count of elements and then the key/value objects
	s.writeInt(table.length);
	s.writeInt(count);
	for (int index = table.length-1; index >= 0; index--) {
	    Entry entry = table[index];

	    while (entry != null) {
		s.writeObject(entry.key);
		s.writeObject(entry.value);
		entry = entry.next;
	    }
	}
    }

    /**
     * Reconstitute the Hashtable from a stream (i.e., deserialize it).
     */
    private void readObject(java.io.ObjectInputStream s)
         throws IOException, ClassNotFoundException
    {
	// Read in the length, threshold, and loadfactor
	s.defaultReadObject();

	// Read the original length of the array and number of elements
	int origlength = s.readInt();
	int elements = s.readInt();

	// Compute new size with a bit of room 5% to grow but
	// No larger than the original size.  Make the length
	// odd if it's large enough, this helps distribute the entries.
	// Guard against the length ending up zero, that's not valid.
	int length = (int)(elements * loadFactor) + (elements / 20) + 3;
	if (length > elements && (length & 1) == 0)
	    length--;
	if (origlength > 0 && length > origlength)
	    length = origlength;

	table = new Entry[length];
	count = 0;

	// Read the number of elements and then all the key/value objects
	for (; elements > 0; elements--) {
	    Object key = s.readObject();
	    Object value = s.readObject();
	    put(key, value);  // synch could be eliminated for performance
	}
    }


    /**
     * Hashtable collision list.
     */
    private static class Entry implements Map.Entry {
	int hash;
	Object key;
	Object value;
	Entry next;

	protected Entry(int hash, Object key, Object value, Entry next) {
	    this.hash = hash;
	    this.key = key;
	    this.value = value;
	    this.next = next;
	}

	protected Object clone() {
	    return new Entry(hash, key, value,
			     (next==null ? null : (Entry)next.clone()));
	}

	// Map.Entry Ops 

	public Object getKey() {
	    return key;
	}

	public Object getValue() {
	    return value;
	}

	public Object setValue(Object value) {
	    if (value == null)
		throw new NullPointerException();

	    Object oldValue = this.value;
	    this.value = value;
	    return oldValue;
	}

	public boolean equals(Object o) {
	    if (!(o instanceof Map.Entry))
		return false;
	    Map.Entry e = (Map.Entry)o;

	    return (key==null ? e.getKey()==null : key.equals(e.getKey())) &&
	       (value==null ? e.getValue()==null : value.equals(e.getValue()));
	}

	public int hashCode() {
	    return hash ^ (value==null ? 0 : value.hashCode());
	}

	public String toString() {
	    return key.toString()+"="+value.toString();
	}
    }

    // Types of Enumerations/Iterations
    private static final int KEYS = 0;
    private static final int VALUES = 1;
    private static final int ENTRIES = 2;

    /**
     * A hashtable enumerator class.  This class implements both the
     * Enumeration and Iterator interfaces, but individual instances
     * can be created with the Iterator methods disabled.  This is necessary
     * to avoid unintentionally increasing the capabilities granted a user
     * by passing an Enumeration.
     */
    private class Enumerator implements Enumeration, Iterator {
	Entry[] table = Hashtable.this.table;
	int index = table.length;
	Entry entry = null;
	Entry lastReturned = null;
	int type;

	/**
	 * Indicates whether this Enumerator is serving as an Iterator
	 * or an Enumeration.  (true -> Iterator).
	 */
	boolean iterator;

	/**
	 * The modCount value that the iterator believes that the backing
	 * List should have.  If this expectation is violated, the iterator
	 * has detected concurrent modification.
	 */
	protected int expectedModCount = modCount;

	Enumerator(int type, boolean iterator) {
	    this.type = type;
	    this.iterator = iterator;
	}

	public boolean hasMoreElements() {
	    Entry e = entry;
	    int i = index;
	    Entry t[] = table;
	    /* Use locals for faster loop iteration */
	    while (e == null && i > 0) { 
		e = t[--i];
	    }
	    entry = e;
	    index = i;
	    return e != null;
	}

	public Object nextElement() {
	    Entry et = entry;
	    int i = index;
	    Entry t[] = table;
	    /* Use locals for faster loop iteration */
	    while (et == null && i > 0) { 
		et = t[--i];
	    }
	    entry = et;
	    index = i;
	    if (et != null) {
		Entry e = lastReturned = entry;
		entry = e.next;
		return type == KEYS ? e.key : (type == VALUES ? e.value : e);
	    }
	    throw new NoSuchElementException("Hashtable Enumerator");
	}

	// Iterator methods
	public boolean hasNext() {
	    return hasMoreElements();
	}

	public Object next() {
	    if (modCount != expectedModCount)
		throw new ConcurrentModificationException();
	    return nextElement();
	}

	public void remove() {
	    if (!iterator)
		throw new UnsupportedOperationException();
	    if (lastReturned == null)
		throw new IllegalStateException("Hashtable Enumerator");
	    if (modCount != expectedModCount)
		throw new ConcurrentModificationException();

	    synchronized(Hashtable.this) {
		Entry[] tab = Hashtable.this.table;
		int index = (lastReturned.hash & 0x7FFFFFFF) % tab.length;

		for (Entry e = tab[index], prev = null; e != null;
		     prev = e, e = e.next) {
		    if (e == lastReturned) {
			modCount++;
			expectedModCount++;
			if (prev == null)
			    tab[index] = e.next;
			else
			    prev.next = e.next;
			count--;
			lastReturned = null;
			return;
		    }
		}
		throw new ConcurrentModificationException();
	    }
	}
    }

   
    private static EmptyEnumerator emptyEnumerator = new EmptyEnumerator();
    private static EmptyIterator emptyIterator = new EmptyIterator();

    /**
     * A hashtable enumerator class for empty hash tables, specializes
     * the general Enumerator
     */
    private static class EmptyEnumerator implements Enumeration {

	EmptyEnumerator() {
	}

	public boolean hasMoreElements() {
	    return false;
	}

	public Object nextElement() {
	    throw new NoSuchElementException("Hashtable Enumerator");
	}
    }


    /**
     * A hashtable iterator class for empty hash tables
     */
    private static class EmptyIterator implements Iterator {

	EmptyIterator() {
	}

	public boolean hasNext() {
	    return false;
	}

	public Object next() {
	    throw new NoSuchElementException("Hashtable Iterator");
	}

	public void remove() {
	    throw new IllegalStateException("Hashtable Iterator");
	}

    }

}