public void map() {

    JavaRDD<Integer> rdd = sc.parallelize(Arrays.asList(1, 2, 3, 4, 5));

    JavaDoubleRDD doubles = rdd.mapToDouble(x -> 1.0 * x).cache();

    doubles.collect();

    JavaPairRDD<Integer, Integer> pairs = rdd.mapToPair(x -> new Tuple2<>(x, x))

      .cache();

    pairs.collect();

    JavaRDD<String> strings = rdd.map(Object::toString).cache();

    strings.collect();

  }