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();
- }
-}