This image gives you quite a lot of help. I would implement this as a base class, (AbstractSevenSegmentDigit) containing booleans if the segment should be printed or not. By default, everything is off.
Then I would create subclasses where I in the constructor sets the segments that are to be lit. The class OneSevenSegmentDigit would look something like this:
What I would like the digits to do is to return to me a two dimensional boolean array that is a multiple of the integer I send into it. Then you can iterate over that array to print "light the board".
Making a separate class for each digit is *very* heavy handed. Instead I would use a single class that can assert or clear the segments individually, and return a collection of asserted segments.
My example stores the state of the display internally as an int value, and has a hard-coded list of values for each digit.
Note that I only added a toString() method to the SegmentDisplay class to illustrate the correctness of the class. I normally wouldn't add a toString() method that contains line separators. The hard-coded Strings in the Segment enum can then also be removed.
The original poster could add a String toLines(int size) method, that returns a String for each line of digit, depending on the length of each segment. These lines can then simply be merged together when there are multiple digits to be printed. For this, methods isHorizontal()/isVertical() could be added to the Segment enum.
The mind is a strange and wonderful thing. I'm not sure that it will ever be able to figure itself out, everything else, maybe. From the atom to the universe, everything, except itself.