Insert element into stream

Question

is there a way to insert an element T into a Stream<T>?

    ArrayList<Foo> foos = new ArrayList<>();
    Foo foo = new Foo();

    Stream<Foo> stream = Stream.concat(foos.stream(), Stream.of(foo));

Is there another way? basically a kind of foo.stream().add(foo)... - of course add() doesn't exist. -

Answer 1

No, there's no other way to add elements to the given stream in standard Java Stream API. Some third-party libraries including my StreamEx library provide additional convenient methods to do this:

Stream<Foo> stream = StreamEx.of(foos).append(foo);

Internally it uses the same concat method.

Similar method is available in jOOL library:

Stream<Foo> stream = Seq.seq(foos).concat(foo);

Answer 2

Assuming that foos don't exist. You can build a Stream with the Stream.Builder instead of an ArrayList like this:

Stream.Builder<Integer> builder = Stream.builder();
for (int i = 0; i < 10; i++) {
    builder.accept(i);
}
Stream<Integer> build = builder.add(50).build();
// ...