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/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.hadoop.hive.ql.exec;

import org.apache.hadoop.hive.ql.udf.UDFType;

/**
 * A User-defined function (UDF) for the use with Hive.
 *
 * New UDF classes need to inherit from this UDF class.
 *
 * Required for all UDF classes: 1. Implement one or more methods named
 * "evaluate" which will be called by Hive. The following are some examples:
 * public int evaluate(); public int evaluate(int a); public double evaluate(int
 * a, double b); public String evaluate(String a, int b, String c);
 *
 * "evaluate" should never be a void method. However it can return "null" if
 * needed.
 */
@UDFType(deterministic = true)
public class UDF {

  /**
   * The resolver to use for method resolution.
   */
  private UDFMethodResolver rslv;

  /**
   * The constructor.
   */
  public UDF() {
    rslv = new DefaultUDFMethodResolver(this.getClass());
  }

  /**
   * The constructor with user-provided UDFMethodResolver.
   */
  protected UDF(UDFMethodResolver rslv) {
    this.rslv = rslv;
  }

  /**
   * Sets the resolver.
   *
   * @param rslv
   *          The method resolver to use for method resolution.
   */
  public void setResolver(UDFMethodResolver rslv) {
    this.rslv = rslv;
  }

  /**
   * Get the method resolver.
   */
  public UDFMethodResolver getResolver() {
    return rslv;
  }

  /**
   * These can be overriden to provide the same functionality as the
   * correspondingly named methods in GenericUDF.
   */
  public String[] getRequiredJars() {
    return null;
  }

  public String[] getRequiredFiles() {
    return null;
  }
}