may supply some method Stream.concat, Stream.append, Stream.prepend

[wjtxyz]

simplify the stream concatenation syntax

static <T> Stream<T> concat2(final Stream<T> ...streams){        
    return Stream.of(streams).flatMap(UnaryOperator.Util.identity());
}

Stream<T> append(T t){
   return Stream.concat(this, Stream.of(t));  
}

Stream<T> prepend(T t){
   return Stream.concat(Stream.of(t), this);
}

[aNNiMON]

Concatenating more than two streams is a good idea. I've start implementing this on #187
In order not to break compatibility (and to avoid concat2 naming), I've created a method

public static <T> Stream<T> concat(
            Stream<? extends T> stream1,
            Stream<? extends T> stream2,
            Stream<? extends T>... rest)

but i think it would be better to replace this with simple

public static <T> Stream<T> concat(
            List<Stream<? extends T>> streams)

So, it will be possible to call the method by passing a dynamically generated list of streams

List<Stream<Integer>> streams = Stream.range(1, 5)
        .flatMap(count -> Stream.range(0, count))
        .toList();
Stream.concat(streams).map(...)

or by specifying all streams statically:

Stream.concat(Arrays.asList(stream1, stream2, stream3)).map(...)