net.sf.javagimmicks.collections.AutoFillingMapDecorator Maven / Gradle / Ivy

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package net.sf.javagimmicks.collections;

import java.util.Map;

import net.sf.javagimmicks.collections.decorators.AbstractMapDecorator;
import net.sf.javagimmicks.util.Supplier;

/**
 * A special {@link Map} decorator that wraps a given {@link Map} and there
 * automatically fills in (default) values if a call to {@link #get(Object)}
 * tries to receive the value for a not yet contained key. This is useful in
 * some special cases e.g. if {@link NullPointerException}s should be avoided
 * and there is some logic for creating default values.
 * 
 * Default values for auto-filling have to be provided/generated via a given
 * {@link Supplier}.
 * 
 * @param 
 *           the type of keys
 * @param 
 *           the type of values
 */
public class AutoFillingMapDecorator extends AbstractMapDecorator
{
   private static final long serialVersionUID = -955460173448590006L;

   /**
    * Decorates a given {@link Map} using the given {@link Supplier} for
    * generating default values.
    * 
    * @param decorated
    *           the {@link Map} to wrap
    * @param valueFactory
    *           the {@link Supplier} to use for generating default values
    * @param 
    *           the type of the keys
    * @param 
    *           the type of the values
    * @return the resulting wrapped {@link Map}
    */
   public static  Map decorate(final Map decorated, final Supplier valueFactory)
   {
      return new AutoFillingMapDecorator(decorated, valueFactory);
   }

   protected final Supplier _valueFactory;

   protected AutoFillingMapDecorator(final Map decorated, final Supplier valueFactory)
   {
      super(decorated);
      _valueFactory = valueFactory;
   }

   /**
    * Re-implements the default behavior in the following way:
    * 

    * If the given key does exist in the underlying {@link Map}, return the
    * associated value (may be null)
    * 
If the given key does not yet exist in the underlying {@link Map}
    * 
    * Call the underlying {@link Supplier} the receive a default value
    * Perform a {@link #put(Object, Object)} with the given key and new
    * default value on the underlying {@link Map}
    * 
Return the default value
    * 
    * 
    */
   @Override
   @SuppressWarnings("unchecked")
   public V get(final Object key)
   {
      if (!containsKey(key))
      {
         put((K) key, _valueFactory.get());
      }

      return super.get(key);
   }
}