true if this hashtable maps no keys to values;
* false 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 containsKey
* method.
*
* @param value a value to search for.
* @return true if some key maps to the
* value argument in this hashtable;
* false otherwise.
* @exception NullPointerException if the value is null.
* @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 true if the specified object is a key in this
* hashtable; false 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;
* null 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 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.
*
* @param key the hashtable key.
* @param value the value.
* @return the previous value of the specified key in this hashtable,
* or null if it did not have one.
* @exception NullPointerException if the key or value is
* null.
* @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 null 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();
}
}