859 lines
24 KiB
Java
859 lines
24 KiB
Java
/* HashMap.java -- a class providing a basic hashtable data structure,
|
|
mapping Object --> Object
|
|
Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
|
|
|
|
This file is part of GNU Classpath.
|
|
|
|
GNU Classpath is free software; you can redistribute it and/or modify
|
|
it under the terms of the GNU General Public License as published by
|
|
the Free Software Foundation; either version 2, or (at your option)
|
|
any later version.
|
|
|
|
GNU Classpath is distributed in the hope that it will be useful, but
|
|
WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
|
General Public License for more details.
|
|
|
|
You should have received a copy of the GNU General Public License
|
|
along with GNU Classpath; see the file COPYING. If not, write to the
|
|
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
|
|
02111-1307 USA.
|
|
|
|
As a special exception, if you link this library with other files to
|
|
produce an executable, this library does not by itself cause the
|
|
resulting executable to be covered by the GNU General Public License.
|
|
This exception does not however invalidate any other reasons why the
|
|
executable file might be covered by the GNU General Public License. */
|
|
|
|
|
|
package java.util;
|
|
|
|
import java.io.IOException;
|
|
import java.io.Serializable;
|
|
import java.io.ObjectInputStream;
|
|
import java.io.ObjectOutputStream;
|
|
import java.io.ObjectStreamField;
|
|
|
|
/**
|
|
* This class provides a hashtable-backed implementation of the
|
|
* Map interface.
|
|
*
|
|
* It uses a hash-bucket approach; that is, hash
|
|
* collisions are handled by linking the new node off of the
|
|
* pre-existing node (or list of nodes). In this manner, techniques
|
|
* such as linear probing (which can casue primary clustering) and
|
|
* rehashing (which does not fit very well with Java's method of
|
|
* precomputing hash codes) are avoided.
|
|
*
|
|
* Under ideal circumstances (no collisions, HashMap offers O(1)
|
|
* performance on most operations (<pre>containsValue()</pre> is,
|
|
* of course, O(n)). In the worst case (all keys map to the same
|
|
* hash code -- very unlikely), most operations are O(n).
|
|
*
|
|
* HashMap is part of the JDK1.2 Collections API. It differs from
|
|
* Hashtable in that it accepts the null key and null values, and it
|
|
* does not support "Enumeration views."
|
|
*
|
|
* @author Jon Zeppieri
|
|
* @version $Revision: 1.6 $
|
|
* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
|
|
*/
|
|
public class HashMap extends AbstractMap
|
|
implements Map, Cloneable, Serializable
|
|
{
|
|
// STATIC (CLASS) VARIABLES ------------------------------------------
|
|
|
|
/**
|
|
* the default capacity for an instance of HashMap -- I think this
|
|
* is low, and perhaps it shoudl be raised; Sun's documentation mildly
|
|
* suggests that this (11) is the correct value, though
|
|
*/
|
|
private static final int DEFAULT_CAPACITY = 11;
|
|
|
|
/** the default load factor of a HashMap */
|
|
private static final float DEFAULT_LOAD_FACTOR = 0.75F;
|
|
|
|
/** used internally to represent the null key */
|
|
private static final HashMap.Null NULL_KEY = new HashMap.Null();
|
|
|
|
/** used internally to parameterize the creation of set/collection views */
|
|
private static final int KEYS = 0;
|
|
|
|
/** used internally to parameterize the creation of set/collection views */
|
|
private static final int VALUES = 1;
|
|
|
|
/** used internally to parameterize the creation of set/collection views */
|
|
private static final int ENTRIES = 2;
|
|
|
|
private static final long serialVersionUID = 362498820763181265L;
|
|
|
|
// INSTANCE VARIABLES -------------------------------------------------
|
|
|
|
/** the capacity of this HashMap: denotes the size of the bucket array */
|
|
transient int capacity;
|
|
|
|
/** the size of this HashMap: denotes the number of key-value pairs */
|
|
private transient int size;
|
|
|
|
/** the load factor of this HashMap: used in computing the threshold
|
|
* @serial
|
|
*/
|
|
float loadFactor;
|
|
|
|
/* the rounded product of the capacity and the load factor; when the number of
|
|
* elements exceeds the threshold, the HashMap calls <pre>rehash()</pre>
|
|
* @serial
|
|
*/
|
|
private int threshold;
|
|
|
|
/**
|
|
* this data structure contains the actual key-value mappings; a
|
|
* <pre>BucketList</pre> is a lightweight linked list of "Buckets",
|
|
* which, in turn, are linked nodes containing a key-value mapping
|
|
* and a reference to the "next" Bucket in the list
|
|
*/
|
|
private transient Bucket[] buckets;
|
|
|
|
/**
|
|
* counts the number of modifications this HashMap has undergone; used by Iterators
|
|
* to know when to throw ConcurrentModificationExceptions (idea ripped-off from
|
|
* Stuart Ballard's AbstractList implementation)
|
|
*/
|
|
private transient int modCount;
|
|
|
|
|
|
// CONSTRUCTORS ---------------------------------------------------------
|
|
|
|
/**
|
|
* construct a new HashMap with the default capacity and the default
|
|
* load factor
|
|
*/
|
|
public HashMap()
|
|
{
|
|
init(DEFAULT_CAPACITY, DEFAULT_LOAD_FACTOR);
|
|
}
|
|
|
|
/**
|
|
* construct a new HashMap with a specific inital capacity and load factor
|
|
*
|
|
* @param initialCapacity the initial capacity of this HashMap (>=0)
|
|
* @param initialLoadFactor the load factor of this HashMap
|
|
* (a misnomer, really, since the load factor of
|
|
* a HashMap does not change)
|
|
*
|
|
* @throws IllegalArgumentException if (initialCapacity < 0) ||
|
|
* (initialLoadFactor > 1.0) ||
|
|
* (initialLoadFactor <= 0.0)
|
|
*/
|
|
public HashMap(int initialCapacity, float initialLoadFactor)
|
|
throws IllegalArgumentException
|
|
{
|
|
if (initialCapacity < 0 || initialLoadFactor <= 0 || initialLoadFactor > 1)
|
|
throw new IllegalArgumentException();
|
|
else
|
|
init(initialCapacity, initialLoadFactor);
|
|
}
|
|
|
|
/**
|
|
* construct a new HashMap with a specific inital capacity
|
|
*
|
|
* @param initialCapacity the initial capacity of this HashMap (>=0)
|
|
*
|
|
* @throws IllegalArgumentException if (initialCapacity < 0)
|
|
*/
|
|
public HashMap(int initialCapacity)
|
|
throws IllegalArgumentException
|
|
{
|
|
if (initialCapacity < 0)
|
|
throw new IllegalArgumentException();
|
|
else
|
|
init(initialCapacity, DEFAULT_LOAD_FACTOR);
|
|
}
|
|
|
|
/**
|
|
* construct a new HashMap from the given Map
|
|
*
|
|
* every element in Map t will be put into this new HashMap
|
|
*
|
|
* @param t a Map whose key / value pairs will be put into
|
|
* the new HashMap. <b>NOTE: key / value pairs
|
|
* are not cloned in this constructor</b>
|
|
*/
|
|
public HashMap(Map t)
|
|
{
|
|
int mapSize = t.size() * 2;
|
|
init(((mapSize > DEFAULT_CAPACITY) ? mapSize : DEFAULT_CAPACITY), DEFAULT_LOAD_FACTOR);
|
|
putAll(t);
|
|
}
|
|
|
|
|
|
// PUBLIC METHODS ---------------------------------------------------------
|
|
|
|
/** returns the number of kay-value mappings currently in this Map */
|
|
public int size()
|
|
{
|
|
return size;
|
|
}
|
|
|
|
/** returns true if there are no key-value mappings currently in this Map */
|
|
public boolean isEmpty()
|
|
{
|
|
return size == 0;
|
|
}
|
|
|
|
/** empties this HashMap of all elements */
|
|
public void clear()
|
|
{
|
|
size = 0;
|
|
modCount++;
|
|
buckets = new Bucket[capacity];
|
|
}
|
|
|
|
/**
|
|
* returns a shallow clone of this HashMap (i.e. the Map itself is cloned, but
|
|
* its contents are not)
|
|
*/
|
|
public Object clone()
|
|
{
|
|
Map.Entry entry;
|
|
Iterator it = entrySet().iterator();
|
|
HashMap clone = new HashMap(capacity, loadFactor);
|
|
while (it.hasNext())
|
|
{
|
|
entry = (Map.Entry) it.next();
|
|
clone.internalPut(entry.getKey(), entry.getValue());
|
|
}
|
|
return clone;
|
|
}
|
|
|
|
/** returns a "set view" of this HashMap's keys */
|
|
public Set keySet()
|
|
{
|
|
return new HashMapSet(KEYS);
|
|
}
|
|
|
|
/** returns a "set view" of this HashMap's entries */
|
|
public Set entrySet()
|
|
{
|
|
return new HashMapSet(ENTRIES);
|
|
}
|
|
|
|
/** returns a "collection view" (or "bag view") of this HashMap's values */
|
|
public Collection values()
|
|
{
|
|
return new HashMapCollection();
|
|
}
|
|
|
|
/**
|
|
* returns true if the supplied object equals (<pre>equals()</pre>) a key
|
|
* in this HashMap
|
|
*
|
|
* @param key the key to search for in this HashMap
|
|
*/
|
|
public boolean containsKey(Object key)
|
|
{
|
|
return (internalGet(key) != null);
|
|
}
|
|
|
|
/**
|
|
* returns true if this HashMap contains a value <pre>o</pre>, such that
|
|
* <pre>o.equals(value)</pre>.
|
|
*
|
|
* @param value the value to search for in this Hashtable
|
|
*/
|
|
public boolean containsValue(Object value)
|
|
{
|
|
int i;
|
|
Bucket list;
|
|
|
|
for (i = 0; i < capacity; i++)
|
|
{
|
|
list = buckets[i];
|
|
if (list != null && list.containsValue(value))
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* return the value in this Hashtable associated with the supplied key, or <pre>null</pre>
|
|
* if the key maps to nothing
|
|
*
|
|
* @param key the key for which to fetch an associated value
|
|
*/
|
|
public Object get(Object key)
|
|
{
|
|
Map.Entry oResult = internalGet(key);
|
|
return (oResult == null) ? null : oResult.getValue();
|
|
}
|
|
|
|
/**
|
|
* puts the supplied value into the Map, mapped by the supplied key
|
|
*
|
|
* @param key the HashMap key used to locate the value
|
|
* @param value the value to be stored in the HashMap
|
|
*/
|
|
public Object put(Object key, Object value)
|
|
{
|
|
return internalPut(key, value);
|
|
}
|
|
|
|
/**
|
|
* removes from the HashMap and returns the value which is mapped by the
|
|
* supplied key; if the key maps to nothing, then the HashMap remains unchanged,
|
|
* and <pre>null</pre> is returned
|
|
*
|
|
* @param key the key used to locate the value to remove from the HashMap
|
|
*/
|
|
public Object remove(Object key)
|
|
{
|
|
Bucket list;
|
|
int index;
|
|
Object result = null;
|
|
if (size > 0)
|
|
{
|
|
index = hash(((key == null) ? NULL_KEY : key));
|
|
list = buckets[index];
|
|
if (list != null)
|
|
{
|
|
result = list.removeByKey(key);
|
|
if (result != null)
|
|
{
|
|
size--;
|
|
modCount++;
|
|
if (list.first == null)
|
|
buckets[index] = null;
|
|
}
|
|
}
|
|
}
|
|
return result;
|
|
}
|
|
|
|
|
|
// PRIVATE METHODS -----------------------------------------------------------
|
|
|
|
/**
|
|
* puts the given key-value pair into this HashMap; a private method is used
|
|
* because it is called by the rehash() method as well as the put() method,
|
|
* and if a subclass overrides put(), then rehash would do funky things
|
|
* if it called put()
|
|
*
|
|
* @param key the HashMap key used to locate the value
|
|
* @param value the value to be stored in the HashMap
|
|
*/
|
|
private Object internalPut(Object key, Object value)
|
|
{
|
|
HashMapEntry entry;
|
|
Bucket list;
|
|
int hashIndex;
|
|
Object oResult;
|
|
Object oRealKey = ((key == null) ? NULL_KEY : key);
|
|
|
|
entry = new HashMapEntry(oRealKey, value);
|
|
hashIndex = hash(oRealKey);
|
|
list = buckets[hashIndex];
|
|
if (list == null)
|
|
{
|
|
list = new Bucket();
|
|
buckets[hashIndex] = list;
|
|
}
|
|
oResult = list.add(entry);
|
|
if (oResult == null)
|
|
{
|
|
modCount++;
|
|
if (size++ == threshold)
|
|
rehash();
|
|
return null;
|
|
}
|
|
else
|
|
{
|
|
// SEH: if key already exists, we don't rehash & we don't update the modCount
|
|
// because it is not a "structural" modification
|
|
return oResult;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* a private method, called by all of the constructors to initialize a new HashMap
|
|
*
|
|
* @param initialCapacity the initial capacity of this HashMap (>=0)
|
|
* @param initialLoadFactor the load factor of this HashMap
|
|
* (a misnomer, really, since the load factor of
|
|
* a HashMap does not change)
|
|
*/
|
|
private void init(int initialCapacity, float initialLoadFactor)
|
|
{
|
|
size = 0;
|
|
modCount = 0;
|
|
capacity = initialCapacity;
|
|
loadFactor = initialLoadFactor;
|
|
threshold = (int) ((float) capacity * loadFactor);
|
|
buckets = new Bucket[capacity];
|
|
}
|
|
|
|
/** private -- simply hashes a non-null Object to its array index */
|
|
private int hash(Object key)
|
|
{
|
|
return Math.abs(key.hashCode() % capacity);
|
|
}
|
|
|
|
/**
|
|
* increases the size of the HashMap and rehashes all keys to new array indices;
|
|
* this is called when the addition of a new value would cause size() > threshold
|
|
*/
|
|
private void rehash()
|
|
{
|
|
int i;
|
|
Bucket[] data = buckets;
|
|
Bucket.Node node;
|
|
|
|
modCount++;
|
|
capacity = (capacity * 2) + 1;
|
|
size = 0;
|
|
threshold = (int) ((float) capacity * loadFactor);
|
|
buckets = new Bucket[capacity];
|
|
for (i = 0; i < data.length; i++)
|
|
{
|
|
if (data[i] != null)
|
|
{
|
|
node = data[i].first;
|
|
while (node != null)
|
|
{
|
|
internalPut(node.getKey(), node.getValue());
|
|
node = node.next;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* a private method which does the "dirty work" (or some of it anyway) of fetching a value
|
|
* with a key
|
|
*
|
|
* @param key the key for which to fetch an associated value
|
|
*/
|
|
private Map.Entry internalGet(Object key)
|
|
{
|
|
Bucket list;
|
|
if (size == 0)
|
|
{
|
|
return null;
|
|
}
|
|
else
|
|
{
|
|
list = buckets[hash(((key == null) ? NULL_KEY : key))];
|
|
return (list == null) ? null : list.getEntryByKey(key);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* a private method used by inner class HashMapSet to implement its own
|
|
* <pre>contains(Map.Entry)</pre> method; returns true if the supplied
|
|
* key / value pair is found in this HashMap (again, using <pre>equals()</pre>,
|
|
* rather than <pre>==</pre>)
|
|
*
|
|
* @param entry a Map.Entry to match against key / value pairs in
|
|
* this HashMap
|
|
*/
|
|
private boolean containsEntry(Map.Entry entry)
|
|
{
|
|
Map.Entry oInternalEntry;
|
|
if (entry == null)
|
|
{
|
|
return false;
|
|
}
|
|
else
|
|
{
|
|
oInternalEntry = internalGet(entry.getKey());
|
|
return (oInternalEntry != null && oInternalEntry.equals(entry));
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Serializes this object to the given stream.
|
|
* @serialdata the <i>capacity</i>(int) that is the length of the
|
|
* bucket array, the <i>size</i>(int) of the hash map are emitted
|
|
* first. They are followed by size entries, each consisting of
|
|
* a key (Object) and a value (Object).
|
|
*/
|
|
private void writeObject(ObjectOutputStream s)
|
|
throws IOException
|
|
{
|
|
// the fields
|
|
s.defaultWriteObject();
|
|
|
|
s.writeInt(capacity);
|
|
s.writeInt(size);
|
|
Iterator it = entrySet().iterator();
|
|
while (it.hasNext())
|
|
{
|
|
Map.Entry oEntry = (Map.Entry) it.next();
|
|
s.writeObject(oEntry.getKey());
|
|
s.writeObject(oEntry.getValue());
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Deserializes this object from the given stream.
|
|
* @serialdata the <i>capacity</i>(int) that is the length of the
|
|
* bucket array, the <i>size</i>(int) of the hash map are emitted
|
|
* first. They are followed by size entries, each consisting of
|
|
* a key (Object) and a value (Object).
|
|
*/
|
|
private void readObject(ObjectInputStream s)
|
|
throws IOException, ClassNotFoundException
|
|
{
|
|
// the fields
|
|
s.defaultReadObject();
|
|
|
|
capacity = s.readInt();
|
|
int iLen = s.readInt();
|
|
size = 0;
|
|
modCount = 0;
|
|
buckets = new Bucket[capacity];
|
|
|
|
for (int i = 0; i < iLen; i++)
|
|
{
|
|
Object oKey = s.readObject();
|
|
Object oValue = s.readObject();
|
|
internalPut(oKey, oValue);
|
|
}
|
|
}
|
|
|
|
// INNER CLASSES -------------------------------------------------------------
|
|
// ---------------------------------------------------------------------------
|
|
|
|
/**
|
|
* an inner class providing a Set view of a HashMap; this implementation is
|
|
* parameterized to view either a Set of keys or a Set of Map.Entry objects
|
|
*
|
|
* Note: a lot of these methods are implemented by AbstractSet, and would work
|
|
* just fine without any meddling, but far greater efficiency can be gained by
|
|
* overriding a number of them. And so I did.
|
|
*
|
|
* @author Jon Zeppieri
|
|
* @version $Revision: 1.6 $
|
|
* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
|
|
*/
|
|
private class HashMapSet extends AbstractSet
|
|
implements Set
|
|
{
|
|
/** the type of this Set view: KEYS or ENTRIES */
|
|
private int setType;
|
|
|
|
/** construct a new HashtableSet with the supplied view type */
|
|
HashMapSet(int type)
|
|
{
|
|
setType = type;
|
|
}
|
|
|
|
/**
|
|
* adding an element is unsupported; this method simply throws an exception
|
|
*
|
|
* @throws UnsupportedOperationException
|
|
*/
|
|
public boolean add(Object o) throws UnsupportedOperationException
|
|
{
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* adding an element is unsupported; this method simply throws an exception
|
|
*
|
|
* @throws UnsupportedOperationException
|
|
*/
|
|
public boolean addAll(Collection c) throws UnsupportedOperationException
|
|
{
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* clears the backing HashMap; this is a prime example of an overridden implementation
|
|
* which is far more efficient than its superclass implementation (which uses an iterator
|
|
* and is O(n) -- this is an O(1) call)
|
|
*/
|
|
public void clear()
|
|
{
|
|
HashMap.this.clear();
|
|
}
|
|
|
|
/**
|
|
* returns true if the supplied object is contained by this Set
|
|
*
|
|
* @param o an Object being testing to see if it is in this Set
|
|
*/
|
|
public boolean contains(Object o)
|
|
{
|
|
if (setType == KEYS)
|
|
return HashMap.this.containsKey(o);
|
|
else
|
|
return (o instanceof Map.Entry) ? HashMap.this.containsEntry((Map.Entry) o) : false;
|
|
}
|
|
|
|
/**
|
|
* returns true if the backing HashMap is empty (which is the only case either a KEYS
|
|
* Set or an ENTRIES Set would be empty)
|
|
*/
|
|
public boolean isEmpty()
|
|
{
|
|
return HashMap.this.isEmpty();
|
|
}
|
|
|
|
/**
|
|
* removes the supplied Object from the Set
|
|
*
|
|
* @param o the Object to be removed
|
|
*/
|
|
public boolean remove(Object o)
|
|
{
|
|
if (setType == KEYS)
|
|
return (HashMap.this.remove(o) != null);
|
|
else
|
|
return (o instanceof Map.Entry) ?
|
|
(HashMap.this.remove(((Map.Entry) o).getKey()) != null) : false;
|
|
}
|
|
|
|
/** returns the size of this Set (always equal to the size of the backing Hashtable) */
|
|
public int size()
|
|
{
|
|
return HashMap.this.size();
|
|
}
|
|
|
|
/** returns an Iterator over the elements of this Set */
|
|
public Iterator iterator()
|
|
{
|
|
return new HashMapIterator(setType);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Like the above Set view, except this one if for values, which are not
|
|
* guaranteed to be unique in a Map; this prvides a Bag of values
|
|
* in the HashMap
|
|
*
|
|
* @author Jon Zeppieri
|
|
* @version $Revision: 1.6 $
|
|
* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
|
|
*/
|
|
private class HashMapCollection extends AbstractCollection
|
|
implements Collection
|
|
{
|
|
/** a trivial contructor for HashMapCollection */
|
|
HashMapCollection()
|
|
{
|
|
}
|
|
|
|
/**
|
|
* adding elements is not supported by this Collection;
|
|
* this method merely throws an exception
|
|
*
|
|
* @throws UnsupportedOperationException
|
|
*/
|
|
public boolean add(Object o) throws UnsupportedOperationException
|
|
{
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/**
|
|
* adding elements is not supported by this Collection;
|
|
* this method merely throws an exception
|
|
*
|
|
* @throws UnsupportedOperationException
|
|
*/
|
|
public boolean addAll(Collection c) throws UnsupportedOperationException
|
|
{
|
|
throw new UnsupportedOperationException();
|
|
}
|
|
|
|
/** removes all elements from this Collection (and from the backing HashMap) */
|
|
public void clear()
|
|
{
|
|
HashMap.this.clear();
|
|
}
|
|
|
|
/**
|
|
* returns true if this Collection contains at least one Object which equals() the
|
|
* supplied Object
|
|
*
|
|
* @param o the Object to compare against those in the Set
|
|
*/
|
|
public boolean contains(Object o)
|
|
{
|
|
return HashMap.this.containsValue(o);
|
|
}
|
|
|
|
/** returns true IFF the Collection has no elements */
|
|
public boolean isEmpty()
|
|
{
|
|
return HashMap.this.isEmpty();
|
|
}
|
|
|
|
/** returns the size of this Collection */
|
|
public int size()
|
|
{
|
|
return HashMap.this.size();
|
|
}
|
|
|
|
/** returns an Iterator over the elements in this Collection */
|
|
public Iterator iterator()
|
|
{
|
|
return new HashMapIterator(VALUES);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* a class which implements the Iterator interface and is used for
|
|
* iterating over HashMaps;
|
|
* this implementation is parameterized to give a sequential view of
|
|
* keys, values, or entries; it also allows the removal of elements,
|
|
* as per the Javasoft spec.
|
|
*
|
|
* @author Jon Zeppieri
|
|
* @version $Revision: 1.6 $
|
|
* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
|
|
*/
|
|
class HashMapIterator implements Iterator
|
|
{
|
|
/** the type of this Iterator: KEYS, VALUES, or ENTRIES */
|
|
private int myType;
|
|
/**
|
|
* the number of modifications to the backing Hashtable for which
|
|
* this Iterator can account (idea ripped off from Stuart Ballard)
|
|
*/
|
|
private int knownMods;
|
|
/** the location of our sequential "cursor" */
|
|
private int position;
|
|
/** the current index of the BucketList array */
|
|
private int bucketIndex;
|
|
/** a reference, originally null, to the specific Bucket our "cursor" is pointing to */
|
|
private Bucket.Node currentNode;
|
|
/** a reference to the current key -- used fro removing elements via the Iterator */
|
|
private Object currentKey;
|
|
|
|
/** construct a new HashtableIterator with the supllied type: KEYS, VALUES, or ENTRIES */
|
|
HashMapIterator(int type)
|
|
{
|
|
myType = type;
|
|
knownMods = HashMap.this.modCount;
|
|
position = 0;
|
|
bucketIndex = -1;
|
|
currentNode = null;
|
|
currentKey = null;
|
|
}
|
|
|
|
/**
|
|
* Stuart Ballard's code: if the backing HashMap has been altered through anything
|
|
* but <i>this</i> Iterator's <pre>remove()</pre> method, we will give up right here,
|
|
* rather than risking undefined behavior
|
|
*
|
|
* @throws ConcurrentModificationException
|
|
*/
|
|
private void checkMod()
|
|
{
|
|
if (knownMods != HashMap.this.modCount)
|
|
throw new ConcurrentModificationException();
|
|
}
|
|
|
|
/** returns true if the Iterator has more elements */
|
|
public boolean hasNext()
|
|
{
|
|
checkMod();
|
|
return position < HashMap.this.size();
|
|
}
|
|
|
|
/** returns the next element in the Iterator's sequential view */
|
|
public Object next()
|
|
{
|
|
Bucket list = null;
|
|
Object result;
|
|
checkMod();
|
|
try
|
|
{
|
|
while (currentNode == null)
|
|
{
|
|
while (list == null)
|
|
list = HashMap.this.buckets[++bucketIndex];
|
|
currentNode = list.first;
|
|
}
|
|
currentKey = currentNode.getKey();
|
|
result = (myType == KEYS) ? currentKey :
|
|
((myType == VALUES) ? currentNode.getValue() : currentNode);
|
|
currentNode = currentNode.next;
|
|
}
|
|
catch(Exception e)
|
|
{
|
|
throw new NoSuchElementException();
|
|
}
|
|
position++;
|
|
return result;
|
|
}
|
|
|
|
/**
|
|
* removes from the backing HashMap the last element which was fetched with the
|
|
* <pre>next()</pre> method
|
|
*/
|
|
public void remove()
|
|
{
|
|
checkMod();
|
|
if (currentKey == null)
|
|
{
|
|
throw new IllegalStateException();
|
|
}
|
|
else
|
|
{
|
|
HashMap.this.remove(currentKey);
|
|
knownMods++;
|
|
position--;
|
|
currentKey = null;
|
|
}
|
|
}
|
|
}
|
|
|
|
/**
|
|
* a singleton instance of this class (HashMap.NULL_KEY)
|
|
* is used to represent the null key in HashMap objects
|
|
*
|
|
* @author Jon Zeppieri
|
|
* @version $Revision: 1.6 $
|
|
* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
|
|
*/
|
|
private static class Null
|
|
{
|
|
/** trivial constructor */
|
|
Null()
|
|
{
|
|
}
|
|
}
|
|
|
|
/**
|
|
* a HashMap version of Map.Entry -- one thing in this implementation is
|
|
* HashMap-specific: if the key is HashMap.NULL_KEY, getKey() will return
|
|
* null
|
|
*
|
|
* Simply, a key / value pair
|
|
*
|
|
* @author Jon Zeppieri
|
|
* @version $Revision: 1.6 $
|
|
* @modified $Id: HashMap.java,v 1.6 2000/03/15 21:59:13 rao Exp $
|
|
*/
|
|
private static class HashMapEntry extends Bucket.Node implements Map.Entry
|
|
{
|
|
/** construct a new HashMapEntry with the given key and value */
|
|
public HashMapEntry(Object key, Object value)
|
|
{
|
|
super(key, value);
|
|
}
|
|
|
|
/**
|
|
* if the key == HashMap.NULL_KEY, null is returned, otherwise the actual
|
|
* key is returned
|
|
*/
|
|
public Object getKey()
|
|
{
|
|
Object oResult = super.getKey();
|
|
return (oResult == HashMap.NULL_KEY) ? null : oResult;
|
|
}
|
|
}
|
|
// EOF -----------------------------------------------------------------------
|
|
}
|