Good start.
Now refactor and add the following methods:
lcd() - return the true Least Common Denominator. LCD of 1/3 and 2/3 is 3, not 9.
reduce() - reduces 2/6 to 1/3
equals() - (new Fraction(1, 3)).equals(new Fraction(2, 6)) should be true
inverse() -
System.out.println((new Fraction(2, 3)).inverse()); // "3/2"
or to make it more interesting, make it printout "1-1/2" (Sorry, I've forgotten all the proper terms for these fractions)
Have fun!