Method of

base/src/main/java/net/time4j/Duration.java:393–428

(
        long amount,
        U unit
    )

     * @return  new duration
     */
    public static <U extends IsoUnit> Duration<U> of(
        long amount,
        U unit
    ) {

        if (amount == 0) {
            return ofZero();
        }

        U u = unit;
        long value = amount;

        if (amount < 0) {
            value = MathUtils.safeNegate(amount);
        }

        if (unit instanceof ClockUnit) {
	        switch (unit.getSymbol()) {
	            case '3':
	                u = cast(ClockUnit.NANOS);
	                value = MathUtils.safeMultiply(value, MIO);
	                break;
	            case '6':
	                u = cast(ClockUnit.NANOS);
	                value = MathUtils.safeMultiply(value, 1000);
	                break;
	            default:
	                // no-op
	        }
        }

        List<Item<U>> items = new ArrayList<>(1);
        items.add(Item.of(value, u));
        return new Duration<>(items, (amount < 0));

    }

    /**
     * <p>Konstructs a new positive duration for combined date- and time items