identityhashtable.java

来自「java jdk 1.4的源码」· Java 代码 · 共 409 行

/*
 * @(#)IdentityHashtable.java	1.9 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

/*
 * Licensed Materials - Property of IBM
 * RMI-IIOP v1.0
 * Copyright IBM Corp. 1998 1999  All Rights Reserved
 *
 * US Government Users Restricted Rights - Use, duplication or
 * disclosure restricted by GSA ADP Schedule Contract with IBM Corp.
 */

package com.sun.corba.se.internal.util;

import java.util.Dictionary;
import java.util.Enumeration;
import java.util.NoSuchElementException;

/**
 * IdentityHashtable collision list.
 */
class IdentityHashtableEntry {
    int hash;
    Object key;
    Object value;
    IdentityHashtableEntry next;
}

/**
 * IdentityHashtable is a modified copy of the 1.1.6 Hashtable class which
 * does not rely on the hashCode() and equals() methods of the key or value; 
 * instead, it uses the System.identityHashcode() method and pointer comparison.
 * In addition, all synchronization has been removed.
 */
public final class IdentityHashtable extends Dictionary {
    /**
     * The hash table data.
     */
    private transient IdentityHashtableEntry table[];

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

    /**
     * Rehashes the table when count exceeds this threshold.
     */
    private int threshold;

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

    /**
     * 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        a number between 0.0 and 1.0.
     * @exception  IllegalArgumentException  if the initial capacity is less
     *               than or equal to zero, or if the load factor is less than
     *               or equal to zero.
     * @since      JDK1.0
     */
    public IdentityHashtable(int initialCapacity, float loadFactor) {
	if ((initialCapacity <= 0) || (loadFactor <= 0.0)) {
	    throw new IllegalArgumentException();
	}
	this.loadFactor = loadFactor;
	table = new IdentityHashtableEntry[initialCapacity];
	threshold = (int)(initialCapacity * loadFactor);
    }

    /**
     * Constructs a new, empty hashtable with the specified initial capacity
     * and default load factor.
     *
     * @param   initialCapacity   the initial capacity of the hashtable.
     * @since   JDK1.0
     */
    public IdentityHashtable(int initialCapacity) {
	this(initialCapacity, 0.75f);
    }

    /**
     * Constructs a new, empty hashtable with a default capacity and load
     * factor. 
     *
     * @since   JDK1.0
     */
    public IdentityHashtable() {
	this(101, 0.75f);
    }

    /**
     * Returns the number of keys in this hashtable.
     *
     * @return  the number of keys in this hashtable.
     * @since   JDK1.0
     */
    public int size() {
	return count;
    }

    /**
     * Tests if this hashtable maps no keys to values.
     *
     * @return  <code>true</code> if this hashtable maps no keys to values;
     *          <code>false</code> otherwise.
     * @since   JDK1.0
     */
    public boolean isEmpty() {
	return count == 0;
    }

    /**
     * Returns an enumeration of the keys in this hashtable.
     *
     * @return  an enumeration of the keys in this hashtable.
     * @see     java.util.Enumeration
     * @see     java.util.Hashtable#elements()
     * @since   JDK1.0
     */
    public Enumeration keys() {
	return new IdentityHashtableEnumerator(table, true);
    }

    /**
     * Returns an enumeration of the values in this hashtable.
     * Use the Enumeration methods on the returned object to fetch the elements
     * sequentially.
     *
     * @return  an enumeration of the values in this hashtable.
     * @see     java.util.Enumeration
     * @see     java.util.Hashtable#keys()
     * @since   JDK1.0
     */
    public Enumeration elements() {
	return new IdentityHashtableEnumerator(table, false);
    }

    /**
     * Tests if some key maps into the specified value in this hashtable.
     * This operation is more expensive than the <code>containsKey</code>
     * method.
     *
     * @param      value   a value to search for.
     * @return     <code>true</code> if some key maps to the
     *             <code>value</code> argument in this hashtable;
     *             <code>false</code> otherwise.
     * @exception  NullPointerException  if the value is <code>null</code>.
     * @see        java.util.Hashtable#containsKey(java.lang.Object)
     * @since      JDK1.0
     */
    public boolean contains(Object value) {
	if (value == null) {
	    throw new NullPointerException();
	}

	IdentityHashtableEntry tab[] = table;
	for (int i = tab.length ; i-- > 0 ;) {
	    for (IdentityHashtableEntry e = tab[i] ; e != null ; e = e.next) {
		if (e.value == value) {
		    return true;
		}
	    }
	}
	return false;
    }

    /**
     * Tests if the specified object is a key in this hashtable.
     * 
     * @param   key   possible key.
     * @return  <code>true</code> if the specified object is a key in this
     *          hashtable; <code>false</code> otherwise.
     * @see     java.util.Hashtable#contains(java.lang.Object)
     * @since   JDK1.0
     */
public boolean containsKey(Object key) {
    IdentityHashtableEntry tab[] = table;
    int hash = System.identityHashCode(key);
    int index = (hash & 0x7FFFFFFF) % tab.length;
    for (IdentityHashtableEntry e = tab[index] ; e != null ; e = e.next) {
	if ((e.hash == hash) && e.key == key) {
	    return true;
	}
    }
    return false;
}

/**
 * Returns the value to which the specified key is mapped in this hashtable.
 *
 * @param   key   a key in the hashtable.
 * @return  the value to which the key is mapped in this hashtable;
 *          <code>null</code> if the key is not mapped to any value in
 *          this hashtable.
 * @see     java.util.Hashtable#put(java.lang.Object, java.lang.Object)
 * @since   JDK1.0
 */
public Object get(Object key) {
    IdentityHashtableEntry tab[] = table;
    int hash = System.identityHashCode(key);
    int index = (hash & 0x7FFFFFFF) % tab.length;
    for (IdentityHashtableEntry e = tab[index] ; e != null ; e = e.next) {
	if ((e.hash == hash) && e.key == key) {
	    return e.value;
	}
    }
    return null;
}

/**
 * Rehashes the contents of the hashtable into a hashtable with a 
 * larger capacity. This method is called automatically when the 
 * number of keys in the hashtable exceeds this hashtable's capacity 
 * and load factor. 
 *
 * @since   JDK1.0
 */
protected void rehash() {
    int oldCapacity = table.length;
    IdentityHashtableEntry oldTable[] = table;

    int newCapacity = oldCapacity * 2 + 1;
    IdentityHashtableEntry newTable[] = new IdentityHashtableEntry[newCapacity];

    threshold = (int)(newCapacity * loadFactor);
    table = newTable;

    //System.out.println("rehash old=" + oldCapacity + ", new=" + newCapacity + ", thresh=" + threshold + ", count=" + count);

    for (int i = oldCapacity ; i-- > 0 ;) {
	for (IdentityHashtableEntry old = oldTable[i] ; old != null ; ) {
	    IdentityHashtableEntry e = old;
	    old = old.next;

	    int index = (e.hash & 0x7FFFFFFF) % newCapacity;
	    e.next = newTable[index];
	    newTable[index] = e;
	}
    }
}

/**
 * Maps the specified <code>key</code> to the specified 
 * <code>value</code> in this hashtable. Neither the key nor the 
 * value can be <code>null</code>. 
 * <p>
 * The value can be retrieved by calling the <code>get</code> method 
 * with a key that is equal to the original key. 
 *
 * @param      key     the hashtable key.
 * @param      value   the value.
 * @return     the previous value of the specified key in this hashtable,
 *             or <code>null</code> if it did not have one.
 * @exception  NullPointerException  if the key or value is
 *               <code>null</code>.
 * @see     java.util.Hashtable#get(java.lang.Object)
 * @since   JDK1.0
 */
public Object put(Object key, Object value) {
    // Make sure the value is not null
    if (value == null) {
	throw new NullPointerException();
    }

    // Makes sure the key is not already in the hashtable.
    IdentityHashtableEntry tab[] = table;
    int hash = System.identityHashCode(key);
    int index = (hash & 0x7FFFFFFF) % tab.length;
    for (IdentityHashtableEntry e = tab[index] ; e != null ; e = e.next) {
	if ((e.hash == hash) && e.key == key) {
	    Object old = e.value;
	    e.value = value;
	    return old;
	}
    }

    if (count >= threshold) {
	// Rehash the table if the threshold is exceeded
	rehash();
	return put(key, value);
    } 

    // Creates the new entry.
    IdentityHashtableEntry e = new IdentityHashtableEntry();
    e.hash = hash;
    e.key = key;
    e.value = value;
    e.next = tab[index];
    tab[index] = e;
    count++;
    return null;
}

    /**
 * Removes the key (and its corresponding value) from this 
 * hashtable. This method does nothing if the key is not in the hashtable.
 *
 * @param   key   the key that needs to be removed.
 * @return  the value to which the key had been mapped in this hashtable,
 *          or <code>null</code> if the key did not have a mapping.
 * @since   JDK1.0
 */
public Object remove(Object key) {
    IdentityHashtableEntry tab[] = table;
    int hash = System.identityHashCode(key);
    int index = (hash & 0x7FFFFFFF) % tab.length;
    for (IdentityHashtableEntry e = tab[index], prev = null ; e != null ; prev = e, e = e.next) {
	if ((e.hash == hash) && e.key == key) {
	    if (prev != null) {
		prev.next = e.next;
	    } else {
		tab[index] = e.next;
	    }
	    count--;
	    return e.value;
	}
    }
    return null;
}

/**
 * Clears this hashtable so that it contains no keys. 
 *
 * @since   JDK1.0
 */
public void clear() {
    IdentityHashtableEntry tab[] = table;
    for (int index = tab.length; --index >= 0; )
	tab[index] = null;
    count = 0;
}

/**
 * Returns a rather long string representation of this hashtable.
 *
 * @return  a string representation of this hashtable.
 * @since   JDK1.0
 */
public String toString() {
    int max = size() - 1;
    StringBuffer buf = new StringBuffer();
    Enumeration k = keys();
    Enumeration e = elements();
    buf.append("{");

    for (int i = 0; i <= max; i++) {
	String s1 = k.nextElement().toString();
	String s2 = e.nextElement().toString();
	buf.append(s1 + "=" + s2);
	if (i < max) {
	    buf.append(", ");
	}
    }
    buf.append("}");
    return buf.toString();
}
}

/**
 * A hashtable enumerator class.  This class should remain opaque 
 * to the client. It will use the Enumeration interface. 
 */
class IdentityHashtableEnumerator implements Enumeration {
    boolean keys;
    int index;
    IdentityHashtableEntry table[];
    IdentityHashtableEntry entry;

    IdentityHashtableEnumerator(IdentityHashtableEntry table[], boolean keys) {
	this.table = table;
	this.keys = keys;
	this.index = table.length;
    }
	
    public boolean hasMoreElements() {
	if (entry != null) {
	    return true;
	}
	while (index-- > 0) {
	    if ((entry = table[index]) != null) {
		return true;
	    }
	}
	return false;
}

public Object nextElement() {
    if (entry == null) {
	while ((index-- > 0) && ((entry = table[index]) == null));
    }
    if (entry != null) {
	    IdentityHashtableEntry e = entry;
	entry = e.next;
	return keys ? e.key : e.value;
    }
	throw new NoSuchElementException("IdentityHashtableEnumerator");
    }
}