/***********************************************************************************************************************
*
* 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.GenericFilter;
/**
* The abstract base class for Filter functions. A filter function take elements and evaluates a
* predicate on them to decide whether to keep the element, or to discard it.
* <p>
* The basic syntax for using a FilterFunction is as follows:
* <pre><blockquote>
* DataSet<X> input = ...;
*
* DataSet<X> result = input.filter(new MyFilterFunction());
* </blockquote></pre>
* <p>
* Like all functions, the FilterFunction needs to be serializable, as defined in {@link java.io.Serializable}.
*
* @param <T> The type of the filtered elements.
*/
public abstract class FilterFunction<T> extends AbstractFunction implements GenericFilter<T> {
private static final long serialVersionUID = 1L;
/**
* The core method of the FilterFunction. The method is called for each element in the input,
* and determines whether the element should be kept or filtered out. If the method returns true,
* the element passes the filter and is kept, if the method returns false, the element is
* filtered out.
*
* @param value The input value to be filtered.
* @return Flag to indicate whether to keep the value (true) or to discard it (false).
*
* @throws Exception This method may throw exceptions. Throwing an exception will cause the operation
* to fail and may trigger recovery.
*/
@Override
public abstract boolean filter(T value) throws Exception;
}