Mega Code Archive
A java util Map interface which can only hold a single object
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/*
* $Id: MicroMap.java 458489 2006-01-04 09:28:14Z ivaynberg $ $Revision:
* 1.4 $ $Date: 2006-01-04 10:28:14 +0100 (Wed, 04 Jan 2006) $
*
*
* Licensed 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.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
*/
public final class MicroMap implements Map, 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 Object key;
/** The value for the only key in this tiny map */
private Object value;
/**
* Constructor
*/
public MicroMap()
{
}
/**
* Constructs map with a single key and value pair.
*
* @param key
* The key
* @param value
* The value
*/
public MicroMap(final Object key, final Object 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 Object 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 Object put(final Object key, final Object value)
{
// Replace?
if (key.equals(this.key))
{
final Object 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 Object remove(final Object key)
{
if (key.equals(this.key))
{
final Object oldValue = this.value;
this.key = null;
this.value = null;
return oldValue;
}
return null;
}
/**
* @see java.util.Map#putAll(java.util.Map)
*/
public void putAll(final Map map)
{
if (map.size() <= MAX_ENTRIES)
{
final Map.Entry e = (Map.Entry)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 keySet()
{
return new AbstractSet()
{
public Iterator iterator()
{
return new Iterator()
{
public boolean hasNext()
{
return index < MicroMap.this.size();
}
public Object next()
{
index++;
return key;
}
public void remove()
{
MicroMap.this.clear();
}
int index;
};
}
public int size()
{
return MicroMap.this.size();
}
};
}
/**
* @see java.util.Map#values()
*/
public Collection values()
{
return new AbstractList()
{
public Object get(final int index)
{
return value;
}
public int size()
{
return MicroMap.this.size();
}
};
}
/**
* @see java.util.Map#entrySet()
*/
public Set entrySet()
{
return new AbstractSet()
{
public Iterator iterator()
{
return new Iterator()
{
public boolean hasNext()
{
return index < MicroMap.this.size();
}
public Object next()
{
index++;
return new Map.Entry()
{
public Object getKey()
{
return key;
}
public Object getValue()
{
return value;
}
public Object setValue(final Object value)
{
final Object oldValue = MicroMap.this.value;
MicroMap.this.value = value;
return oldValue;
}
};
}
public void remove()
{
clear();
}
int index = 0;
};
}
public int size()
{
return MicroMap.this.size();
}
};
}
}
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