Aggregator.java

package org.openflamingo.mapreduce.aggregator;


import org.apache.hadoop.io.Writable;

/**
 * Interface for Aggregator.  Allows aggregate operations for all vertices
 * in a given superstep.
 *
 * @param <A> Aggregated value
 */
public interface Aggregator<A extends Writable> {
	/**
	 * Add a new value.
	 * Needs to be commutative and associative
	 *
	 * @param value Value to be aggregated.
	 */
	void aggregate(A value);

	/**
	 * Set aggregated value.
	 * Can be used for initialization or reset.
	 *
	 * @param value Value to be set.
	 */
	void setAggregatedValue(A value);

	/**
	 * Return current aggregated value.
	 * Needs to be initialized if aggregate or setAggregatedValue
	 * have not been called before.
	 *
	 * @return Aggregated
	 */
	A getAggregatedValue();

	/**
	 * Return new aggregated value.
	 * Must be changeable without affecting internals of Aggregator
	 *
	 * @return Writable
	 */
	A createAggregatedValue();
}