spark中迭代器的使用（求最大或最小）

import java.util.Arrays;
import java.util.List;
import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaPairRDD;
import org.apache.spark.api.java.JavaSparkContext;
import jersey.repackaged.com.google.common.collect.Lists;
import scala.Tuple2;
public class groupbykey {
  public static void main(String[] args) {
    // TODO Auto-generated method stub
    SparkConf conf=new SparkConf().setAppName("").setMaster("local");
    JavaSparkContext sc=new JavaSparkContext(conf);
    List<Tuple2<String,Integer>> scores=Arrays.asList(
        new Tuple2<String,Integer>("jac",80),
        new Tuple2<String,Integer>("jac",100),
        new Tuple2<String,Integer>("jac",70),
        new Tuple2<String,Integer>("gs",80),
        new Tuple2<String,Integer>("gs",90)
        );
    JavaPairRDD<String,Integer> pardd=sc.parallelizePairs(scores);
    JavaPairRDD<String,Iterable<Integer>> pardd1=pardd.groupByKey();
    JavaPairRDD<String,Integer> pardd2=
        pardd1.mapValues(f->{
      List<Integer> li=Lists.newArrayList(f);//迭代器转list
      Integer j=0;
      for(int i=0;i<li.size();i++) {
        if(li.get(i)>j) {
          j=li.get(i);
        }
      }
      return j;
    });
    pardd2.foreach(f->System.out.println(f));
  }
}