No, the primary reason is that a mandolin has wire/steel strings, an ukulele uses gut or nylon. The tension required for a steel string is not going to be good for the instrument. Other reasons: They...
Typically the top and bottom strings are doubled. They often are an octave apart which gives the instrument a fuller sound, but are played the same way as one with only 4 strings.
The related question below talks about the various tunings and strings for an ukulele. The mechanical process is pretty straightforward for those that can be done with a simple knot at the bridge...