package com.suning.udf;import org.apache.hadoop.hive.ql.exec.UDAF;import org.apache.hadoop.hive.ql.exec.UDAFEvaluator;public class Avg extends UDAF {    public static class AvgState {        private long mCount;        private double mSum;    }    public static class AvgEvaluator implements UDAFEvaluator {        AvgState state;        public AvgEvaluator() {            super();            state = new AvgState();            init();        }        /**         * init函数类似于构造函数，用于UDAF的初始化         */        public void init() {            state.mSum = 0;            state.mCount = 0;        }        /**         * iterate接收传入的参数，并进行内部的轮转。其返回类型为boolean * * @param o * @return         */        public boolean iterate(Double o) {            if (o != null) {                state.mSum += o;                state.mCount++;            }            return true;        }        /**         * terminatePartial无参数，其为iterate函数遍历结束后，返回轮转数据， * terminatePartial类似于hadoop的Combiner * * @return         */        public AvgState terminatePartial() {            // combiner            return state.mCount == 0 ? null : state;        }        /**         * merge接收terminatePartial的返回结果，进行数据merge操作，其返回类型为boolean * * @param o * @return         */        public boolean merge(AvgState avgState) {            if (avgState != null) {                state.mCount += avgState.mCount;                state.mSum += avgState.mSum;            }            return true;        }        /**         * terminate返回最终的聚集函数结果 * * @return         */        public Double terminate() {            return state.mCount == 0 ? null : Double.valueOf(state.mSum / state.mCount);        }    }}