As Ray points out, there is danger in allowing any sort of iterating if we
automatically clear entries on get(). Since the point of this is to be a cache and not to be iterable, we will simply remove all but the safe and necessary functionality to keep people out of trouble. Keep it simple! Put things it, get them out. Or not. git-svn-id: https://samskivert.googlecode.com/svn/trunk@1886 6335cc39-0255-0410-8fd6-9bcaacd3b74c
This commit is contained in:
mdb
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//
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// samskivert library - useful routines for java programs
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// Copyright (C) 2001-2006 Michael Bayne
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//
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// This library is free software; you can redistribute it and/or modify it
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// under the terms of the GNU Lesser General Public License as published
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// by the Free Software Foundation; either version 2.1 of the License, or
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// (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public
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// License along with this library; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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package com.samskivert.util;
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import java.lang.ref.SoftReference;
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import java.util.HashMap;
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import java.util.Map;
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/**
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* Implements a {@link SoftReference} cache wherein the values in the hashmap
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* are not prevented from being garbage collected.
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*/
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public class SoftCache<K,V>
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{
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public SoftCache (int initialCapacity, float loadFactor)
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{
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_map = new HashMap<K,SoftReference<V>>(initialCapacity, loadFactor);
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}
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public SoftCache (int initialCapacity)
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{
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_map = new HashMap<K,SoftReference<V>>(initialCapacity);
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}
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public SoftCache ()
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{
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_map = new HashMap<K,SoftReference<V>>();
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}
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/**
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* Returns true if the supplied key exists in this map and is mapped to an
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* active value.
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*/
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public boolean containsKey (K key)
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{
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return (get(key) != null);
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}
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/**
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* Looks up and returns the value associated with the supplied key.
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*/
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public V get (K key)
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{
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V value = null;
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SoftReference<V> ref = _map.get(key);
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if (ref != null) {
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value = ref.get();
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if (value == null) {
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_map.remove(key);
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}
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}
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return value;
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}
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/**
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* Maps the specified key to the specified value.
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*/
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public V put (K key, V value)
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{
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SoftReference<V> old = _map.put(key, new SoftReference<V>(value));
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return (old == null) ? null : old.get();
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}
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/**
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* Removes the specified key from the map. Returns the value to which the
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* key was previously mapped or null.
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*/
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public V remove (K key)
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{
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SoftReference<V> ref = _map.remove(key);
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return (ref == null) ? null : ref.get();
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}
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/**
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* Clears all mappings.
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*/
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public void clear ()
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{
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_map.clear();
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}
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protected HashMap<K,SoftReference<V>> _map;
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}
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@@ -1,169 +0,0 @@
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//
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// samskivert library - useful routines for java programs
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// Copyright (C) 2001-2006 Michael Bayne
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//
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// This library is free software; you can redistribute it and/or modify it
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// under the terms of the GNU Lesser General Public License as published
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// by the Free Software Foundation; either version 2.1 of the License, or
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// (at your option) any later version.
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//
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// Lesser General Public License for more details.
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//
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// You should have received a copy of the GNU Lesser General Public
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// License along with this library; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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package com.samskivert.util;
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import java.lang.ref.SoftReference;
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import java.util.AbstractMap;
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import java.util.AbstractSet;
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import java.util.Collection;
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import java.util.HashMap;
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import java.util.Iterator;
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import java.util.Map;
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import java.util.Set;
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/**
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* Implements a {@link SoftReference} cache wherein the values in the hashmap
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* are not prevented from being garbage collected.
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*
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* <p><em>Beware!</em> if you iterate over the contents of this map, some
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* values may be null. Also note that if you try to store null values in this
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* map, those entries will be pruned because the map cannot distinguish between
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* an expired soft reference and a null value. Why would you cache null anyway?
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*/
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public class SoftCacheMap<K,V> extends AbstractMap<K,V>
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{
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public SoftCacheMap (int initialCapacity, float loadFactor)
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{
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_map = new HashMap<K,SoftReference<V>>(initialCapacity, loadFactor);
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}
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public SoftCacheMap (int initialCapacity)
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{
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_map = new HashMap<K,SoftReference<V>>(initialCapacity);
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}
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public SoftCacheMap ()
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{
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_map = new HashMap<K,SoftReference<V>>();
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}
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// from interface Map
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public int size ()
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{
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return _map.size();
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}
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// from interface Map
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public boolean containsKey (Object key)
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{
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return (get(key) != null);
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}
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// from interface Map
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public V get (Object key)
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{
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V value = null;
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SoftReference<V> ref = _map.get(key);
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if (ref != null) {
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value = ref.get();
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if (value == null) {
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_map.remove(key);
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}
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}
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return value;
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}
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// from interface Map
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public V put (K key, V value)
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{
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SoftReference<V> old = _map.put(key, new SoftReference<V>(value));
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return (old == null) ? null : old.get();
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}
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// from interface Map
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public V remove (Object key)
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{
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SoftReference<V> ref = _map.remove(key);
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return (ref == null) ? null : ref.get();
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}
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// from interface Map
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public void clear ()
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{
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_map.clear();
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}
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// from interface Map
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public Set<K> keySet ()
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{
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return _map.keySet();
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}
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// from interface Map
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public Set<Entry<K,V>> entrySet ()
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{
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return new EntrySet();
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}
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/**
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* Used by {@link EntrySet}.
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*/
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protected Entry<K,V> getEntry (Object key)
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{
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SoftReference<V> value = _map.get(key);
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@SuppressWarnings("unchecked") K ckey = (K)key;
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return (value == null) ? null : new MapEntry<K,V>(ckey, value.get());
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}
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protected class EntrySet extends AbstractSet<Entry<K,V>> {
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public Iterator<Entry<K,V>> iterator () {
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final Iterator<Entry<K,SoftReference<V>>> iter =
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_map.entrySet().iterator();
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return new Iterator<Entry<K,V>>() {
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public boolean hasNext () {
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return iter.hasNext();
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}
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public Entry<K,V> next () {
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Entry<K,SoftReference<V>> ent = iter.next();
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return (ent == null) ? null :
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new MapEntry<K,V>(ent.getKey(), ent.getValue().get());
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}
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public void remove () {
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iter.remove();
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}
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};
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}
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public boolean contains (Object o) {
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if (!(o instanceof Entry)) {
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return false;
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}
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@SuppressWarnings("unchecked") Entry<K,V> entry = (Entry<K,V>)o;
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return containsKey(entry.getKey());
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}
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public boolean remove (Object o) {
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if (!(o instanceof Entry)) {
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return false;
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}
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@SuppressWarnings("unchecked") Entry<K,V> entry = (Entry<K,V>)o;
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return remove(entry.getKey());
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}
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public int size () {
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return _map.size();
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}
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public void clear () {
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_map.clear();
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}
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}
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protected HashMap<K,SoftReference<V>> _map;
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}
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