I notice that you use lot of "if" statements alone. i.e:

if(something)
(There should be something her before going to the next if, or use { } between
the next statements if they are dependant on the above one )
if(somethinglese)


As I understand the problem, you need to use else { } between all of what
follows:

if (isLeap == false)
System.out.println ("It is unknown " + year  + " is a leap
year.");


else

{

the rest of the program

}


Try it and let me know if that makes or doesn't make sense.