Acme.IntHashtable Maven / Gradle / Ivy
// IntHashtable - a Hashtable that uses ints as the keys
//
// This is 90% based on JavaSoft's java.util.Hashtable.
//
// Visit the ACME Labs Java page for up-to-date versions of this and other
// fine Java utilities: http://www.acme.com/java/
package Acme;
import java.util.Dictionary;
import java.util.Enumeration;
import java.util.NoSuchElementException;
/// A Hashtable that uses ints as the keys.
//
// 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.
@Override
public int size() {
return count;
}
/// Returns true if the hashtable contains no elements.
@Override
public boolean isEmpty() {
return count == 0;
}
/// Returns an enumeration of the hashtable's keys.
// @see IntHashtable#elements
@Override
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
@Override
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.
@Override
public Object get(Object okey) {
if (!(okey instanceof Integer))
throw new InternalError("key is not an Integer");
Integer ikey = (Integer) okey;
int key = ikey;
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;
threshold = (int) (newCapacity * loadFactor);
IntHashtableEntry[] newTable = new IntHashtableEntry[newCapacity];
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.
@Override
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;
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.
@Override
public Object remove(Object okey) {
if (!(okey instanceof Integer))
throw new InternalError("key is not an Integer");
Integer ikey = (Integer) okey;
int key = ikey;
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.
@Override
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;
StringBuilder buf = new StringBuilder();
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).append('=').append(s2);
if (i < max)
buf.append(", ");
}
buf.append('}');
return buf.toString();
}
}
class IntHashtableEntry {
int hash;
int key;
Object value;
IntHashtableEntry next;
@Override
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;
}
@Override
public boolean hasMoreElements() {
if (entry != null)
return true;
while (index-- > 0)
if ((entry = table[index]) != null)
return true;
return false;
}
@Override
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");
}
}