java.util.Hashtable except that: The overall result is that it's less expensive to use these in
* performance-critical locations, in terms both of CPU and memory,
* than java.util.Hashtable instances. In this package
* it makes a significant difference when normalizing attributes,
* which is done for each start-element construct.
*
* @version $Revision: 1.2 $
*/
final class SimpleHashtable implements Enumeration {
// entries ...
private Entry table[];
// currently enumerated key
private Entry current = null;
private int currentBucket = 0;
private int count;
private int threshold;
private static final float loadFactor = 0.75f;
/**
* Constructs a new, empty hashtable with the specified initial
* capacity.
*
* @param initialCapacity the initial capacity of the hashtable.
*/
public SimpleHashtable(int initialCapacity) {
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: " +
initialCapacity);
if (initialCapacity == 0)
initialCapacity = 1;
table = new Entry[initialCapacity];
threshold = (int) (initialCapacity * loadFactor);
}
/**
* Constructs a new, empty hashtable with a default capacity.
*/
public SimpleHashtable() {
this(11);
}
/**
*/
public void clear() {
count = 0;
currentBucket = 0;
current = null;
for (int i = 0; i < table.length; i++)
table[i] = null;
}
/**
* Returns the number of keys in this hashtable.
*
* @return the number of keys in this hashtable.
*/
public int size() {
return count;
}
/**
* Returns an enumeration of the keys in this hashtable.
*
* @return an enumeration of the keys in this hashtable.
* @see Enumeration
*/
public Enumeration keys() {
currentBucket = 0;
current = null;
return this;
}
/**
* Used to view this as an enumeration; returns true if there
* are more keys to be enumerated.
*/
public boolean hasMoreElements() {
if (current != null)
return true;
while (currentBucket < table.length) {
current = table[currentBucket++];
if (current != null)
return true;
}
return false;
}
/**
* Used to view this as an enumeration; returns the next key
* in the enumeration.
*/
public Object nextElement() {
Object retval;
if (current == null)
throw new IllegalStateException();
retval = current.key;
current = current.next;
return retval;
}
/**
* Returns the value to which the specified key is mapped in this hashtable.
*/
public Object get(String key) {
Entry tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entry e = tab[index]; e != null; e = e.next) {
if ((e.hash == hash) && (e.key == key))
return e.value;
}
return null;
}
/**
* Returns the value to which the specified key is mapped in this
* hashtable ... the key isn't necessarily interned, though.
*/
public Object getNonInterned(String key) {
Entry tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entry e = tab[index]; e != null; e = e.next) {
if ((e.hash == hash) && e.key.equals(key))
return e.value;
}
return null;
}
/**
* Increases the capacity of and internally reorganizes this
* hashtable, in order to accommodate and access its entries more
* efficiently. This method is called automatically when the
* number of keys in the hashtable exceeds this hashtable's capacity
* and load factor.
*/
private void rehash() {
int oldCapacity = table.length;
Entry oldMap[] = table;
int newCapacity = oldCapacity * 2 + 1;
Entry newMap[] = new Entry[newCapacity];
threshold = (int) (newCapacity * loadFactor);
table = newMap;
/*
System.out.println("rehash old=" + oldCapacity
+ ", new=" + newCapacity
+ ", thresh=" + threshold
+ ", count=" + count);
*/
for (int i = oldCapacity; i-- > 0;) {
for (Entry old = oldMap[i]; old != null;) {
Entry e = old;
old = old.next;
int index = (e.hash & 0x7FFFFFFF) % newCapacity;
e.next = newMap[index];
newMap[index] = e;
}
}
}
/**
* Maps the specified key to the specified
* value in this hashtable. Neither the key nor the
* value can be null.
*
The value can be retrieved by calling the get method
* with a key that is equal to the original key.
*/
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.
Entry tab[] = table;
int hash = key.hashCode();
int index = (hash & 0x7FFFFFFF) % tab.length;
for (Entry e = tab[index]; e != null; e = e.next) {
// if ((e.hash == hash) && e.key.equals(key)) {
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();
tab = table;
index = (hash & 0x7FFFFFFF) % tab.length;
}
// Creates the new entry.
Entry e = new Entry(hash, key, value, tab[index]);
tab[index] = e;
count++;
return null;
}
/**
* Hashtable collision list.
*/
private static class 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;
}
}
}