org.apache.hadoop.hive.ql.exec.UDAF Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* 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,
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*/
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);
*
*/
@Deprecated
public class UDAF {
/**
* The resolver used for method resolution.
*/
UDAFEvaluatorResolver rslv;
/**
* The default constructor.
*/
public UDAF() {
rslv = new DefaultUDAFEvaluatorResolver(this.getClass());
}
/**
* The constructor with a particular type of resolver.
*/
public UDAF(UDAFEvaluatorResolver rslv) {
this.rslv = rslv;
}
/**
* Sets the resolver.
*
* @param rslv
* The method resolver to use for method resolution.
*/
public void setResolver(UDAFEvaluatorResolver rslv) {
this.rslv = rslv;
}
/**
* Gets the resolver.
*/
public UDAFEvaluatorResolver getResolver() {
return rslv;
}
}