Mega Code Archive
An implementation of the java util Map interface which can only hold a single object
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/*
* 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;
/**
* An implementation of the java.util.Map interface which can only hold a single object. This is
* particularly useful to control memory usage in Wicket because many containers hold only a single
* component.
*
* @author Jonathan Locke
* @param <K>
* Key type
* @param <V>
* Value type
*/
public final class MicroMap<K, V> implements Map<K, V>, Serializable
{
private static final long serialVersionUID = 1L;
/** The maximum number of entries this map supports. */
public static final int MAX_ENTRIES = 1;
/** The one and only key in this tiny map */
private K key;
/** The value for the only key in this tiny map */
private V value;
/**
* Constructor
*/
public MicroMap()
{
}
/**
* Constructs map with a single key and value pair.
*
* @param key
* The key
* @param value
* The value
*/
public MicroMap(final K key, final V value)
{
put(key, value);
}
/**
* @return True if this MicroMap is full
*/
public boolean isFull()
{
return size() == MAX_ENTRIES;
}
/**
* @see java.util.Map#size()
*/
public int size()
{
return (key != null) ? 1 : 0;
}
/**
* @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 key.equals(this.key);
}
/**
* @see java.util.Map#containsValue(java.lang.Object)
*/
public boolean containsValue(final Object value)
{
return value.equals(this.value);
}
/**
* @see java.util.Map#get(java.lang.Object)
*/
public V get(final Object key)
{
if (key.equals(this.key))
{
return value;
}
return null;
}
/**
* @see java.util.Map#put(java.lang.Object, java.lang.Object)
*/
public V put(final K key, final V value)
{
// Replace?
if (key.equals(this.key))
{
final V oldValue = this.value;
this.value = value;
return oldValue;
}
else
{
// Is there room for a new entry?
if (size() < MAX_ENTRIES)
{
// Store
this.key = key;
this.value = value;
return null;
}
else
{
throw new IllegalStateException("Map full");
}
}
}
/**
* @see java.util.Map#remove(java.lang.Object)
*/
public V remove(final Object key)
{
if (key.equals(this.key))
{
final V oldValue = value;
this.key = null;
value = null;
return oldValue;
}
return null;
}
/**
* @see java.util.Map#putAll(java.util.Map)
*/
public void putAll(final Map< ? extends K, ? extends V> map)
{
if (map.size() <= MAX_ENTRIES)
{
final Entry< ? extends K, ? extends V> e = map.entrySet().iterator().next();
put(e.getKey(), e.getValue());
}
else
{
throw new IllegalStateException("Map full. Cannot add " + map.size() + " entries");
}
}
/**
* @see java.util.Map#clear()
*/
public void clear()
{
key = null;
value = null;
}
/**
* @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 index < MicroMap.this.size();
}
public K next()
{
if (!hasNext())
{
throw new NoSuchElementException();
}
index++;
return key;
}
public void remove()
{
MicroMap.this.clear();
}
int index;
};
}
@Override
public int size()
{
return MicroMap.this.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();
}
return value;
}
@Override
public int size()
{
return MicroMap.this.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 < MicroMap.this.size();
}
public Entry<K, V> next()
{
if (!hasNext())
{
throw new NoSuchElementException();
}
index++;
return new Map.Entry<K, V>()
{
public K getKey()
{
return key;
}
public V getValue()
{
return value;
}
public V setValue(final V value)
{
final V oldValue = MicroMap.this.value;
MicroMap.this.value = value;
return oldValue;
}
};
}
public void remove()
{
clear();
}
int index = 0;
};
}
@Override
public int size()
{
return MicroMap.this.size();
}
};
}
}
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