/*
* @(#)Hashtable.java 1.31 95/12/01
*
* Copyright (c) 1994 Sun Microsystems, Inc. All Rights Reserved.
*
* Permission to use, copy, modify, and distribute this software
* and its documentation for NON-COMMERCIAL purposes and without
* fee is hereby granted provided that this copyright notice
* appears in all copies. Please refer to the file "copyright.html"
* for further important copyright and licensing information.
*
* SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF
* THE SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
* TO THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
* PARTICULAR PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR
* ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR
* DISTRIBUTING THIS SOFTWARE OR ITS DERIVATIVES.
*/
package java.util;
/**
* Hashtable collision list.
*/
class HashtableEntry {
int hash;
Object key;
Object value;
HashtableEntry next;
protected Object clone() {
HashtableEntry entry = new HashtableEntry();
entry.hash = hash;
entry.key = key;
entry.value = value;
entry.next = (next != null) ? (HashtableEntry)next.clone() : null;
return entry;
}
}
/**
* Hashtable class. Maps keys to values. Any object can be used as
* a key and/or value.<p>
*
* To sucessfully store and retrieve objects from a hash table the
* object used as the key must implement the hashCode() and equals()
* methods.<p>
*
* This example creates a hashtable of numbers. It uses the names of
* the numbers as keys:
* <pre>
* Hashtable numbers = new Hashtable();
* numbers.put("one", new Integer(1));
* numbers.put("two", new Integer(2));
* numbers.put("three", new Integer(3));
* </pre>
* To retrieve a number use:
* <pre>
* Integer n = (Integer)numbers.get("two");
* if (n != null) {
* System.out.println("two = " + n);
* }
* </pre>
*
* @see java.lang.Object#hashCode
* @see java.lang.Object#equals
* @version 1.31, 01 Dec 1995
* @author Arthur van Hoff
*/
public
class Hashtable extends Dictionary implements Cloneable {
/**
* The hash table data.
*/
private HashtableEntry table[];
/**
* The total number of entries in the hash table.
*/
private 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 number of buckets
* @param loadFactor a number between 0.0 and 1.0, it defines
* the threshold for rehashing the hashtable into
* a bigger one.
* @exception IllegalArgumentException If the initial capacity
* is less than or equal to zero.
* @exception IllegalArgumentException If the load factor is
* less than or equal to zero.
*/
public Hashtable(int initialCapacity, float loadFactor) {
if ((initialCapacity <= 0) || (loadFactor <= 0.0)) {
throw new IllegalArgumentException();
}
this.loadFactor = loadFactor;
table = new HashtableEntry[initialCapacity];
threshold = (int)(initialCapacity * loadFactor);
}
/**
* Constructs a new, empty hashtable with the specified initial
* capacity.
* @param initialCapacity the initial number of buckets
*/
public Hashtable(int initialCapacity) {
this(initialCapacity, 0.75f);
}
/**
* Constructs a new, empty hashtable. A default capacity and load factor
* is used. Note that the hashtable will automatically grow when it gets
* full.
*/
public Hashtable() {
this(101, 0.75f);
}
/**
* Returns the number of elements contained in the hashtable.
*/
public int size() {
return count;
}
/**
* Returns true if the hashtable contains no elements.
*/
public boolean isEmpty() {
return count == 0;
}
/**
* Returns an enumeration of the hashtable's keys.
* @see Hashtable#elements
* @see Enumeration
*/
public synchronized Enumeration keys() {
return new HashtableEnumerator(table, true);
}
/**
* Returns an enumeration of the elements. Use the Enumeration methods
* on the returned object to fetch the elements sequentially.
* @see Hashtable#keys
* @see Enumeration
*/
public synchronized Enumeration elements() {
return new HashtableEnumerator(table, false);
}
/**
* Returns true if the specified object is an element of the hashtable.
* This operation is more expensive than the containsKey() method.
* @param value the value that we are looking for
* @exception NullPointerException If the value being searched
* for is equal to null.
* @see Hashtable#containsKey
*/
public synchronized boolean contains(Object value) {
if (value == null) {
throw new NullPointerException();
}
HashtableEntry tab[] = table;
for (int i = tab.length ; i-- > 0 ;) {
for (HashtableEntry e = tab[i] ; e != null ; e = e.next) {
if (e.value.equals(value)) {
return true;
}
}
}
return false;
}
/**
* Returns true if the collection contains an element for the key.
* @param key the key that we are looking for
* @see Hashtable#contains
*/
public synchronized boolean containsKey(Object key) {
HashtableEntry tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (HashtableEntry e = tab[index] ; e != null ; e = e.next) {
if ((e.hash == hash) && e.key.equals(key)) {
return true;
}
}
return false;
}
/**
* Gets the object associated with the specified key in the
* hashtable.
* @param key the specified key
* @returns the element for the key or null if the key
* is not defined in the hash table.
* @see Hashtable#put
*/
public synchronized Object get(Object key) {
HashtableEntry tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (HashtableEntry e = tab[index] ; e != null ; e = e.next) {
if ((e.hash == hash) && e.key.equals(key)) {
return e.value;
}
}
return null;
}
/**
* Rehashes the content of the table into a bigger table.
* This method is called automatically when the hashtable's
* size exceeds the threshold.
*/
protected void rehash() {
int oldCapacity = table.length;
HashtableEntry oldTable[] = table;
int newCapacity = oldCapacity * 2 + 1;
HashtableEntry newTable[] = new HashtableEntry[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 (HashtableEntry old = oldTable[i] ; old != null ; ) {
HashtableEntry e = old;
old = old.next;
int index = (e.hash & 0x7FFFFFFF) % newCapacity;
e.next = newTable[index];
newTable[index] = e;
}
}
}
/**
* Puts the specified element into the hashtable, using the specified
* key. The element may be retrieved by doing a get() with the same key.
* The key and the element cannot be null.
* @param key the specified key in the hashtable
* @param value the specified element
* @exception NullPointerException If the value of the element
* is equal to null.
* @see Hashtable#get
* @return the old value of the key, or null if it did not have one.
*/
public synchronized 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.
HashtableEntry tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (HashtableEntry e = tab[index] ; e != null ; e = e.next) {
if ((e.hash == hash) && e.key.equals(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.
HashtableEntry e = new HashtableEntry();
e.hash = hash;
e.key = key;
e.value = value;
e.next = tab[index];
tab[index] = e;
count++;
return null;
}
/**
* Removes the element corresponding to the key. Does nothing if the
* key is not present.
* @param key the key that needs to be removed
* @return the value of key, or null if the key was not found.
*/
public synchronized Object remove(Object key) {
HashtableEntry tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (HashtableEntry e = tab[index], prev = null ; e != null ; prev = e, e = e.next) {
if ((e.hash == hash) && e.key.equals(key)) {
if (prev != null) {
prev.next = e.next;
} else {
tab[index] = e.next;
}
count--;
return e.value;
}
}
return null;
}
/**
* Clears the hash table so that it has no more elements in it.
*/
public synchronized void clear() {
HashtableEntry tab[] = table;
for (int index = tab.length; --index >= 0; )
tab[index] = null;
count = 0;
}
/**
* Creates a clone of the hashtable. A shallow copy is made,
* the keys and elements themselves are NOT cloned. This is a
* relatively expensive operation.
*/
public synchronized Object clone() {
try {
Hashtable t = (Hashtable)super.clone();
t.table = new HashtableEntry[table.length];
for (int i = table.length ; i-- > 0 ; ) {
t.table[i] = (table[i] != null)
? (HashtableEntry)table[i].clone() : null;
}
return t;
} catch (CloneNotSupportedException e) {
// this shouldn't happen, since we are Cloneable
throw new InternalError();
}
}
/**
* Converts to a rather lengthy String.
*/
public synchronized 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 HashtableEnumerator implements Enumeration {
boolean keys;
int index;
HashtableEntry table[];
HashtableEntry entry;
HashtableEnumerator(HashtableEntry 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) {
HashtableEntry e = entry;
entry = e.next;
return keys ? e.key : e.value;
}
throw new NoSuchElementException("HashtableEnumerator");
}
}