/***********************************************************************************************************************
 * Copyright (C) 2010-2013 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.api.java.record.functions;

import eu.stratosphere.api.common.functions.AbstractFunction;
import eu.stratosphere.api.common.functions.GenericJoiner;
import eu.stratosphere.types.Record;
import eu.stratosphere.util.Collector;

/**
 * The JoinFunction must implementation by functions of a {@link JoinOperator}.
 * It resembles an equality join of both inputs on their key fields.
 */
public abstract class JoinFunction extends AbstractFunction implements GenericJoiner<Record, Record, Record> {
	
	private static final long serialVersionUID = 1L;
	
	/**
	 * This method must be implemented to provide a user implementation of a join.
	 * It is called for each two records that share the same key and come from different inputs.
	 * 
	 * @param value1 The record that comes from the first input.
	 * @param value2 The record that comes from the second input.
	 * @param out A collector that collects all output pairs.
	 * 
	 * @throws Exception Implementations may forward exceptions, which are caught by the runtime. When the
	 *                   runtime catches an exception, it aborts the combine task and lets the fail-over logic
	 *                   decide whether to retry the combiner execution.
	 */
	@Override
	public abstract void join(Record value1, Record value2, Collector<Record> out) throws Exception;
}