question: @ SuppressWarnings ( { "unchecked" } ) @ Override default LazyFutureStream < U > concat ( final Stream < ? extends U > other ) { return fromStream ( Stream . concat ( StreamSupport . stream ( Spliterators . spliteratorUnknownSize ( iterator ( ) , Spliterator . ORDERED ) , false ) , StreamSupport . stream ( Spliterators . spliteratorUnknownSize ( other . iterator ( ) , Spliterator . ORDERED ) , false ) ) ) ; }
target:  Concatenate two streams. // (1, 2, 3, 4, 5, 6) LazyFutureStream.of(1, 2, 3).concat(LazyFutureStream.of(4, 5, 6))