Please post your code between code tags, not quote tags.
From this line:
String tokens = threeWord.split("");
the variable tokens is intended to be AN ARRAY of String objects or literals. However, since the quotes in your call to the split() method are empty, I'm not sure what you'll get. Assuming the user will enter spaces between the words, add a space between the quotes.
Then, this line
if(tokens > 4)
can be changed to:
if( tokens.length > 4 ),
but I think you mean '> 3' rather than '> 4'. And then your if statement needs a body that makes sense.