/***********************************************************************************************************************
*
* 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.functions;
import eu.stratosphere.api.common.functions.AbstractFunction;
import eu.stratosphere.api.common.functions.GenericCrosser;
import eu.stratosphere.util.Collector;
/**
* The abstract base class for Cross functions. Cross functions build a Cartesian produce of their inputs
* and call the function or each pair of elements.
* They are a means of convenience and can be used to directly produce manipulate the
* pair of elements, instead of having the operator build 2-tuples, and then using a
* MapFunction over those 2-tuples.
* <p>
* The basic syntax for using Cross on two data sets is as follows:
* <pre><blockquote>
* DataSet<X> set1 = ...;
* DataSet<Y> set2 = ...;
*
* set1.cross(set2).with(new MyCrossFunction());
* </blockquote></pre>
* <p>
* {@code set1} is here considered the first input, {@code set2} the second input.
* <p>
* All functions need to be serializable, as defined in {@link java.io.Serializable}.
*
* @param <IN1> The type of the elements in the first input.
* @param <IN2> The type of the elements in the second input.
* @param <OUT> The type of the result elements.
*/
public abstract class CrossFunction<IN1, IN2, OUT> extends AbstractFunction implements GenericCrosser<IN1, IN2, OUT>{
private static final long serialVersionUID = 1L;
/**
* The core method of the cross operation. The method will be invoked for each pair of elements
* in the Cartesian product.
*
* @param first The element from the first input.
* @param second The element from the second input.
* @return The result element.
*
* @throws Exception This method may throw exceptions. Throwing an exception will cause the operation
* to fail and may trigger recovery.
*/
public abstract OUT cross(IN1 first, IN2 second) throws Exception;
/**
* This method only delegates calls to the {@link #cross(Object, Object)} method.
*/
@Override
public final void cross(IN1 record1, IN2 record2, Collector<OUT> out) throws Exception {
out.collect(cross(record1, record2));
}
}