A fixed size map implementation.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
import java.io.Serializable;
import java.util.AbstractList;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* A fixed size map implementation. Holds an array of keys and array of values which correspond by
* index. Null key entries are available for use. This means that null is not a valid key.
*
* @author Jonathan Locke
* @param <K>
* Key type
* @param <V>
* Value type
*/
public class MiniMap<K, V> implements Map<K, V>, Serializable
{
private static final long serialVersionUID = 1L;
/** The array of keys. Keys that are null are not used. */
private final K[] keys;
/** The array of values which correspond by index with the keys array. */
private final V[] values;
/** The number of valid entries */
private int size;
/** The last search index. This makes putting and getting more efficient. */
private int lastSearchIndex;
/**
* Constructor
*
* @param maxEntries
* The maximum number of entries this map can hold
*/
@SuppressWarnings("unchecked")
public MiniMap(final int maxEntries)
{
keys = (K[])new Object[maxEntries];
values = (V[])new Object[maxEntries];
}
/**
* Constructor
*
* @param map
* The map
* @param maxEntries
* The maximum number of entries this map can hold
*/
public MiniMap(final Map<? extends K, ? extends V> map, final int maxEntries)
{
this(maxEntries);
putAll(map);
}
/**
* @return True if this MicroMap is full
*/
public boolean isFull()
{
return size == keys.length;
}
/**
* @see java.util.Map#size()
*/
public int size()
{
return size;
}
/**
* @see java.util.Map#isEmpty()
*/
public boolean isEmpty()
{
return size == 0;
}
/**
* @see java.util.Map#containsKey(java.lang.Object)
*/
public boolean containsKey(final Object key)
{
return findKey(0, key) != -1;
}
/**
* @see java.util.Map#containsValue(java.lang.Object)
*/
public boolean containsValue(final Object value)
{
return findValue(0, value) != -1;
}
/**
* @see java.util.Map#get(java.lang.Object)
*/
public V get(final Object key)
{
// Search for key
final int index = findKey(key);
if (index != -1)
{
// Return value
return values[index];
}
// Failed to find key
return null;
}
/**
* @see java.util.Map#put(java.lang.Object, java.lang.Object)
*/
public V put(final K key, final V value)
{
// Search for key
final int index = findKey(key);
if (index != -1)
{
// Replace existing value
final V oldValue = values[index];
values[index] = value;
return oldValue;
}
// Is there room for a new entry?
if (size < keys.length)
{
// Store at first null index and continue searching after null index
// next time
final int nullIndex = nextNullKey(lastSearchIndex);
lastSearchIndex = nextIndex(nullIndex);
keys[nullIndex] = key;
values[nullIndex] = value;
size++;
return null;
}
else
{
throw new IllegalStateException("Map full");
}
}
/**
* @see java.util.Map#remove(java.lang.Object)
*/
public V remove(final Object key)
{
// Search for key
final int index = findKey(key);
if (index != -1)
{
// Store value
final V oldValue = values[index];
keys[index] = null;
values[index] = null;
size--;
return oldValue;
}
return null;
}
/**
* @see java.util.Map#putAll(java.util.Map)
*/
public void putAll(Map<? extends K, ? extends V> map)
{
for (final Iterator<? extends Entry<? extends K, ? extends V>> iterator = map.entrySet()
.iterator(); iterator.hasNext();)
{
final Map.Entry<? extends K, ? extends V> e = iterator.next();
put(e.getKey(), e.getValue());
}
}
/**
* @see java.util.Map#clear()
*/
public void clear()
{
for (int i = 0; i < keys.length; i++)
{
keys[i] = null;
values[i] = null;
}
size = 0;
}
/**
* @see java.util.Map#keySet()
*/
public Set<K> keySet()
{
return new AbstractSet<K>()
{
@Override
public Iterator<K> iterator()
{
return new Iterator<K>()
{
public boolean hasNext()
{
return i < size - 1;
}
public K next()
{
// Just in case... (WICKET-428)
if (!hasNext())
{
throw new NoSuchElementException();
}
// Find next key
i = nextKey(nextIndex(i));
// Get key
return keys[i];
}
public void remove()
{
keys[i] = null;
values[i] = null;
size--;
}
int i = -1;
};
}
@Override
public int size()
{
return size;
}
};
}
/**
* @see java.util.Map#values()
*/
public Collection<V> values()
{
return new AbstractList<V>()
{
@Override
public V get(final int index)
{
if (index > size - 1)
{
throw new IndexOutOfBoundsException();
}
int keyIndex = nextKey(0);
for (int i = 0; i < index; i++)
{
keyIndex = nextKey(keyIndex + 1);
}
return values[keyIndex];
}
@Override
public int size()
{
return size;
}
};
}
/**
* @see java.util.Map#entrySet()
*/
public Set<Entry<K, V>> entrySet()
{
return new AbstractSet<Entry<K, V>>()
{
@Override
public Iterator<Entry<K, V>> iterator()
{
return new Iterator<Entry<K, V>>()
{
public boolean hasNext()
{
return index < size;
}
public Entry<K, V> next()
{
if (!hasNext())
{
throw new NoSuchElementException();
}
keyIndex = nextKey(nextIndex(keyIndex));
index++;
return new Map.Entry<K, V>()
{
public K getKey()
{
return keys[keyIndex];
}
public V getValue()
{
return values[keyIndex];
}
public V setValue(final V value)
{
final V oldValue = values[keyIndex];
values[keyIndex] = value;
return oldValue;
}
};
}
public void remove()
{
keys[keyIndex] = null;
values[keyIndex] = null;
}
int keyIndex = -1;
int index = 0;
};
}
@Override
public int size()
{
return size;
}
};
}
/**
* Computes the next index in the key or value array (both are the same length)
*
* @param index
* The index
* @return The next index, taking into account wraparound
*/
private int nextIndex(final int index)
{
return (index + 1) % keys.length;
}
/**
* Finds the index of the next non-null key. If the map is empty, -1 will be returned.
*
* @param start
* Index to start at
* @return Index of next non-null key
*/
private int nextKey(final int start)
{
int i = start;
do
{
if (keys[i] != null)
{
return i;
}
i = nextIndex(i);
}
while (i != start);
return -1;
}
/**
* Finds the index of the next null key. If no null key can be found, the map is full and -1
* will be returned.
*
* @param start
* Index to start at
* @return Index of next null key
*/
private int nextNullKey(final int start)
{
int i = start;
do
{
if (keys[i] == null)
{
return i;
}
i = nextIndex(i);
}
while (i != start);
return -1;
}
/**
* Finds a key by starting at lastSearchIndex and searching from there. If the key is found,
* lastSearchIndex is advanced so the next key search can find the next key in the array, which
* is the most likely to be retrieved.
*
* @param key
* Key to find in map
* @return Index of matching key or -1 if not found
*/
private int findKey(final Object key)
{
if (size > 0)
{
// Find key starting at search index
final int index = findKey(lastSearchIndex, key);
// Found match?
if (index != -1)
{
// Start search at the next index next time
lastSearchIndex = nextIndex(index);
// Return index of key
return index;
}
}
return -1;
}
/**
* Searches for a key from a given starting index.
*
* @param key
* The key to find in this map
* @param start
* Index to start at
* @return Index of matching key or -1 if not found
*/
private int findKey(final int start, final Object key)
{
int i = start;
do
{
if (key.equals(keys[i]))
{
return i;
}
i = nextIndex(i);
}
while (i != start);
return -1;
}
/**
* Searches for a value from a given starting index.
*
* @param start
* Index to start at
* @param value
* The value to find in this map
* @return Index of matching value or -1 if not found
*/
private int findValue(final int start, final Object value)
{
int i = start;
do
{
if (value.equals(values[i]))
{
return i;
}
i = nextIndex(i);
}
while (i != start);
return -1;
}
}
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