Source Code : A java.util.Map interface which can only hold a single object

Java Is Open Source Programming Language You Can Download From Java and Java Libraries From http://www.oracle.com. Click Here to download
We provide this code related to title for you to solve your developing problem easily. Libraries which is import in this program you can download from http://www.oracle.com. Click Here or search from google with Libraries Name you get jar file related it

A java.util.Map interface which can only hold a single object

    
/*
 * $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();
      }
    };
  }
}

   
    
    
    
  

Thank with us