- Direct Known Subclasses:
- NumericUDAF, UDAFPercentile, UDAFTestMax, UDAFWrongArgLengthForTestCase
public class UDAF
extends java.lang.Object
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);