// Use just like java.util.Hashtable, except that the keys must be ints. // This is much faster than creating a new Integer for each access. //
// Fetch the software.
// Fetch the entire Acme package.
//
// @see java.util.Hashtable
public class IntHashtable extends Dictionary implements Cloneable
{
/// The hash table data.
private IntHashtableEntry 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 IntHashtable( int initialCapacity, float loadFactor )
{
if ( initialCapacity <= 0 || loadFactor <= 0.0 )
throw new IllegalArgumentException();
this.loadFactor = loadFactor;
table = new IntHashtableEntry[initialCapacity];
threshold = (int) ( initialCapacity * loadFactor );
}
/// Constructs a new, empty hashtable with the specified initial
// capacity.
// @param initialCapacity the initial number of buckets
public IntHashtable( 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 IntHashtable()
{
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 IntHashtable#elements
public synchronized Enumeration keys()
{
return new IntHashtableEnumerator( table, true );
}
/// Returns an enumeration of the elements. Use the Enumeration methods
// on the returned object to fetch the elements sequentially.
// @see IntHashtable#keys
public synchronized Enumeration elements()
{
return new IntHashtableEnumerator( 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 IntHashtable#containsKey
public synchronized boolean contains( Object value )
{
if ( value == null )
throw new NullPointerException();
IntHashtableEntry tab[] = table;
for ( int i = tab.length ; i-- > 0 ; )
{
for ( IntHashtableEntry 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 IntHashtable#contains
public synchronized boolean containsKey( int key )
{
IntHashtableEntry tab[] = table;
int hash = key;
int index = ( hash & 0x7FFFFFFF ) % tab.length;
for ( IntHashtableEntry e = tab[index] ; e != null ; e = e.next )
{
if ( e.hash == hash && e.key == 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 IntHashtable#put
public synchronized Object get( int key )
{
IntHashtableEntry tab[] = table;
int hash = key;
int index = ( hash & 0x7FFFFFFF ) % tab.length;
for ( IntHashtableEntry e = tab[index] ; e != null ; e = e.next )
{
if ( e.hash == hash && e.key == key )
return e.value;
}
return null;
}
/// A get method that takes an Object, for compatibility with
// java.util.Dictionary. The Object must be an Integer.
public Object get( Object okey )
{
if ( ! ( okey instanceof Integer ) )
throw new InternalError( "key is not an Integer" );
Integer ikey = (Integer) okey;
int key = ikey.intValue();
return get( key );
}
/// 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;
IntHashtableEntry oldTable[] = table;
int newCapacity = oldCapacity * 2 + 1;
IntHashtableEntry newTable[] = new IntHashtableEntry[newCapacity];
threshold = (int) ( newCapacity * loadFactor );
table = newTable;
for ( int i = oldCapacity ; i-- > 0 ; )
{
for ( IntHashtableEntry old = oldTable[i] ; old != null ; )
{
IntHashtableEntry 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 IntHashtable#get
// @return the old value of the key, or null if it did not have one.
public synchronized Object put( int 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.
IntHashtableEntry tab[] = table;
int hash = key;
int index = ( hash & 0x7FFFFFFF ) % tab.length;
for ( IntHashtableEntry 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.
IntHashtableEntry e = new IntHashtableEntry();
e.hash = hash;
e.key = key;
e.value = value;
e.next = tab[index];
tab[index] = e;
++count;
return null;
}
/// A put method that takes an Object, for compatibility with
// java.util.Dictionary. The Object must be an Integer.
public Object put( Object okey, Object value )
{
if ( ! ( okey instanceof Integer ) )
throw new InternalError( "key is not an Integer" );
Integer ikey = (Integer) okey;
int key = ikey.intValue();
return put( key, value );
}
/// 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( int key )
{
IntHashtableEntry tab[] = table;
int hash = key;
int index = ( hash & 0x7FFFFFFF ) % tab.length;
for ( IntHashtableEntry 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;
}
/// A remove method that takes an Object, for compatibility with
// java.util.Dictionary. The Object must be an Integer.
public Object remove( Object okey )
{
if ( ! ( okey instanceof Integer ) )
throw new InternalError( "key is not an Integer" );
Integer ikey = (Integer) okey;
int key = ikey.intValue();
return remove( key );
}
/// Clears the hash table so that it has no more elements in it.
public synchronized void clear()
{
IntHashtableEntry 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
{
IntHashtable t = (IntHashtable) super.clone();
t.table = new IntHashtableEntry[table.length];
for ( int i = table.length ; i-- > 0 ; )
t.table[i] = ( table[i] != null ) ?
(IntHashtableEntry) 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();
}
}
class IntHashtableEntry
{
int hash;
int key;
Object value;
IntHashtableEntry next;
protected Object clone()
{
IntHashtableEntry entry = new IntHashtableEntry();
entry.hash = hash;
entry.key = key;
entry.value = value;
entry.next = ( next != null ) ? (IntHashtableEntry) next.clone() : null;
return entry;
}
}
class IntHashtableEnumerator implements Enumeration
{
boolean keys;
int index;
IntHashtableEntry table[];
IntHashtableEntry entry;
IntHashtableEnumerator( IntHashtableEntry 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 )
{
IntHashtableEntry e = entry;
entry = e.next;
return keys ? new Integer( e.key ) : e.value;
}
throw new NoSuchElementException( "IntHashtableEnumerator" );
}
}
/* */