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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;

Base class for all User-defined Aggregation Function (UDAF) classes. UDAF classes are REQUIRED to inherit from this class. Required for a UDAF class: 1. Implement the init() method, which reset the status of the aggregation function. 2. Implement a single method called "aggregate" that returns boolean. The method should always return "true" on valid inputs, or the framework will throw an Exception. Following are some examples: public boolean aggregate(double a); public boolean aggregate(int b); public boolean aggregate(double c, double d); 3. Implement a single method called "evaluate" that returns the FINAL aggregation result. "evaluate" should never return "null" or an Exception will be thrown. Following are some examples. public int evaluate(); public long evaluate(); public double evaluate(); public Double evaluate(); public String evaluate(); Optional for a UDAF class (by implementing these 2 methods, the user declares that the UDAF support partial aggregations): 1. Implement a single method called "evaluatePartial" that returns the PARTIAL aggregation result. "evaluatePartial" should never return "null" or an Exception will be thrown. 2. Implement a single method called "aggregatePartial" that takes a PARTIAL aggregation result and returns a boolean. The method should always return "true" on valid inputs, or the framework will throw an Exception. Following are some examples: public int evaluatePartial(); public boolean aggregatePartial(int partial); public String evaluatePartial(); public boolean aggregatePartial(String partial);
public class UDAF {

  
The resolver used for method resolution.
The default constructor.
  public UDAF() {
     = new DefaultUDAFEvaluatorResolver(this.getClass());
  }

  
The constructor with a particular type of resolver.
  public UDAF(UDAFEvaluatorResolver rslv) {
    this. = rslv;
  }

  
Sets the resolver.

Parameters:
rslv The method resolver to use for method resolution.
  public void setResolver(UDAFEvaluatorResolver rslv) {
    this. = rslv;
  }

  
Gets the resolver.
    return ;
  }
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