Java 8 Lambdas - equivalent of c# OfType

Question

I am learning the new java 8 features now, after 4 years exclusively in C# world, so lambdas are on top for me. I am now struggling to find an equivalent for C#\'s \"OfType\" me

Answer 1

Instead of first filtering and then mapping the stream to the desired target type, it is possible to do both in a single call to the stream via flatMap and this small helper function:

private static  Function> ofType(Class targetType) {
    return value -> targetType.isInstance(value) ? Stream.of(targetType.cast(value)) : Stream.empty();
}

This Function basically checks for a element if a cast is possible and then casts it, returning a stream with the single casted element or an empty stream if the cast was not possible.

Stream.of(1, 2, 3, "Hallo", 4, 5, "Welt")
    .flatMap(ofType(String.class))
    .forEach(System.out::println);

With the help of a flatMap operation all returned streams can be concatenated.

I assume that a separated check and cast are easier to understand and maybe even faster in execution, this is just a prove of concept for a single stream operation.