Question

this peice of code initialises X as a new formatter variable.

 private Formatter X;
     public void Create() {
                    try{
                        X = new Formatter("users.txt");
                        X.format("%1$20s %2$20s %3$20s %4$20s %5$20s %6$20s %7$20s %8$20s %9$20s \n","Firstname","Lastname","Password","ID","Addressln1","Addressln2","Addressln3","EstimatedValue","Tax Owed");
                        System.out.println("Due to there not being any users file present one has been created.");
                    }
                    catch(Exception e){
                        System.out.println("There is a users file present so i will not create another one.");
                    }
                }
            }

This is the piece of code i am having trouble with , at the X.format bit , it keeps giving me a null pointer error and i have tried everything to fix it.

public void WriteToFilecmd(){
                Scanner input = new Scanner(System.in);
                System.out.println("Please enter your First name");
                String Fname = input.next();
                System.out.println("Please enter your Last name");
                String Lname = input.next();
                System.out.println("Please enter your Password");
                String Password = input.next();
                System.out.println("Please enter your user ID");
                String ID = input.next();
                System.out.println("Please enter the first address line of your Property");
                String addressln1 = input.next();
                System.out.println("Please enter the second address line of your Property");
                String addressln2 = input.next();
                System.out.println("Please enter the third address line of your Property");
                String addressln3 = input.next();
                System.out.println("Please enter the properties estimated market value");
                String EstimatedPropertyValue = input.next();
                System.out.println("Please enter your tax owed");
                String Taxowed = input.next();
                input.close();
                X.format("%1$20s %2$20s %3$20s %4$20s %5$20s %6$20s %7$20s %8$20s %9$20s \n",Fname,Lname,Password,ID,addressln1,addressln2,addressln3,EstimatedPropertyValue,Taxowed);


    }

Answer 1

NullPointerException on the line

X.format("%1$20s %2$20s %3$20s %4$20s %5$20s %6$20s %7$20s %8$20s %9$20s \n",Fname,Lname,Password,ID,addressln1,addressln2,addressln3,EstimatedPropertyValue,Taxowed);

means either that X itself is null, or the method throws it. Normally, Java foundation classes handle null arguments very well (and Scanner#next() does not return null anyways) and don’t contain bugs, so X is most likely null at the moment it’s being used.

This could happen if your create method catches an exception (see the console output), you overwrite X later or if you don’t call the create method at all or you call it too late.

Also note that pokemon exception handling (“gotta catch them all”, catch(Exception e)) is a bad practice. Catch what you can handle, not what you can catch.