src/main/java/io/reactivex/subjects/UnicastSubject.java
@CheckReturnValue
    @NonNull
    public static <T> UnicastSubject<T> create(int capacityHint) {
        return new UnicastSubject<T>(capacityHint, true);
    }
@CheckReturnValue
    @NonNull
    public static <T> UnicastSubject<T> create(int capacityHint) {
        return new UnicastSubject<T>(capacityHint, true);
    }
Creates an UnicastSubject with the given internal buffer capacity hint.
@param <T> the value type
@param capacityHint the hint to size the internal unbounded buffer
@return an UnicastSubject instance