/***********************************************************************************************************************
 *
 * Copyright (C) 2012 by the Stratosphere project (http://stratosphere.eu)
 *
 * 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.
 *
 **********************************************************************************************************************/

package eu.stratosphere.pact.generic.types;

/**
 * This interface defines the method required by the runtime to use data types in join-like operations.
 * In such operations, instances of different data types are compared for equality with respect to certain
 * attributes, such as join keys.
 * 
 * The class compares instances of two different data types. One is always used as the reference data type,
 * and the other is checked against the reference. An instance of the reference data type is normally set as the
 * reference for comparisons. Afterwards one or more instances of the other data type are checked against the
 * reference.
 * 
 * @param <T1> The class of the first data type.
 * @param <T2> The class of the second data type. 
 */
public abstract class TypePairComparator<T1, T2>
{
	/**
	 * Sets the reference for comparisons.
	 * 
	 * @param reference The reference instance.
	 */
	public abstract void setReference(T1 reference);
	
	/**
	 * Checks, whether the given candidate instance is equal to the reference instance, with respect
	 * to this comparator's equality definition.
	 * 
	 * @param candidate The candidate to check.
	 * @return True, if the candidate is equal to the reference, false otherwise.
	 */
	public abstract boolean equalToReference(T2 candidate);
	
	public abstract int compareToReference(T2 candidate);
}
