In a previous post I gave a way of generating random test mobile numbers (Ofcom approved!) using Scala iterators.

Now that Java 8 gives us lambdas and streams I thought I would see what those generators might look like in Java.

Here’s the mobile generator:

Supplier<String> mobileSupplier = () -> String.format("447700900%03d", ThreadLocalRandom.current().nextInt(999));

Nice, still a one-liner.

Generating pseudo MAC addresses is a little bit more trouble. This supplier uses another nested stream to generate the random hex array.

Supplier<String> macSupplier = () -> ThreadLocalRandom.current().ints(6, 0, 255)
        .mapToObj(i -> String.format("%02x", i))
        .collect(Collectors.joining(":"));

You use these Supplier functions with the static generate method of Stream. Because the generators create infinite streams we use limit to just get a few values. Eg:

import java.util.concurrent.ThreadLocalRandom;
import java.util.function.Supplier;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Generators {

    private static final Supplier<String> mobileSupplier = () -> String.format("447700900%03d", ThreadLocalRandom.current().nextInt(999));

    private static final Supplier<String> macSupplier = () -> ThreadLocalRandom.current().ints(6, 0, 255)
            .mapToObj(i -> String.format("%02x", i))
            .collect(Collectors.joining(":"));

    public static void main(String[] args) {
        System.out.println("Some mobile numbers:");
        Stream.generate(Generators.mobileSupplier)
                .limit(5)
                .forEach(System.out::println);
        System.out.println();

        System.out.println("Some (pseudo) mac addresses:");
        Stream.generate(Generators.macSupplier)
                .limit(5)
                .forEach(System.out::println);
    }
}