The action max returns the largest value in the RDD where the comparison between the elements is decided by the comparator passed as an argument:

Java 7:

// max()
JavaRDD<Integer> intRDD = sparkContext.parallelize(Arrays.asList(1,2,3));
Integer maxVal=intRDD.max(new integerComparator());
System.out.println("The max value of RDD is "+maxVal);
//Also create a Comparator class as below
static class integer Comparator implements Comparator<Integer>, Serializable
{
  private static finallongserialVersionUID = 1L;
  @Override
  public int compare(Integer a, Integer b) {
    return a.compareTo(b);
  }
}

Java 8:

JavaRDD<Integer> intRDD = sparkContext.parallelize(Arrays.asList(1,2,3));
Integer maxVal=intRDD.max(Comparator.naturalOrder());
System.out.println("The max value of RDD is "+maxVal);