public static Tween stretch(double desiredLength, Tween... delegates) {
        if (delegates.length == 1) {
            return new Stretch(delegates[0], desiredLength);
        }
        return new Stretch(sequence(delegates), desiredLength);
    }
Creates a tween that scales the specified delegate tween or tweens
to the desired length.  If more than one tween is specified then they
are wrapped in a sequence using the sequence() method.

@param desiredLength the desired duration (in seconds)
@param delegates the desired sequence of tweens
@return a new instance
jme3-core/src/main/java/com/jme3/anim/tween/Tweens.java