Implementing a method that calculates the factorial of a number, with exception

Question

public class fakultaet1 {

    public static long fakultaet(long n)   {
        if (n<0)
            throw new FakultaetNichtDefiniertException(n);
         if (n==0)
            return 1;
          long fakultaet = 1;       
            while(n>1){
              fakultaet *= n;  // had a litte mistake here
             n--;
        }
        return fakultaet;   
    }

    public class FakultaetNichtDefiniertException extends RuntimeException{
        public FakultaetNichtDefiniertException(long n){
            super("Die Fakultät is für den Wert "+ n +" nicht definiert.");
        }
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
            System.out.println(fakultaet(5));
    }
}

So i want my code to calculate the factorial of the input n, and it should throw an Exception when the number is less than 0, but if i try to run it gives me this output.

 Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
 No enclosing instance of type fakultaet1 is accessible. Must qualify the 
 allocation with an enclosing instance of type fakultaet1 (e.g. x.new A() 
 where x is an instance of fakultaet1).

at klausur_ws1718.fakultaet1.fakultaet(fakultaet1.java:8)
at klausur_ws1718.fakultaet1.main(fakultaet1.java:29)

I do not really understand the Error. Thanks in advance.

if `n==0` you immediately `return 1`, making the rest of the code unreachable. Edit: I think. The lack of `{}` and indents makes it hard for me to read your if statements. Sorry if it is a single-line. — , May 17 '18 at 13:07
The whole thing is messed up somehow. You can only have **one** public class per class. So it looks like you are **not** showing the full class here. Thus: look into [mcve] and improve your question accordingly. And "unresolved compilation" problem basically means: it doesn't even compile. So, even when eclipse allows to do that: when your class doesnt compile, dont run it! — GhostCat, May 17 '18 at 13:09

score 5 · Accepted Answer · answered May 17 '18 at 13:07

You defined the FakultaetNichtDefiniertException class as an inner class of fakultaet1, which means you can only create an instance of it if you supply an instance of the enclosing fakultaet1 class. This doesn't make much sense.

You can either move the exception class out of fakultaet1, or make it a nested class (static), which doesn't require an enclosing instance:

static class FakultaetNichtDefiniertException extends RuntimeException{
    public FakultaetNichtDefiniertException(long n){
        super("Die Fakultät is für den Wert "+ n +" nicht definiert.");
    } 
}

Thank you, i wasn't even thinking about it that way! – RYU5 May 17 '18 at 13:14 — RYU5, May 17 '18 at 13:14

score 1 · Answer 2 · answered May 17 '18 at 13:21

Your FakultaetNichtDefiniertException class is an inner class of class fakultaet1. You cannot instantiate an object of an inner class if there is no instance of the enclosing class available in the scope. A possible solution is to make the inner class static. Another solution is to define the inner class as a normal class, outside of the enclosing class.

Java - No enclosing instance of type Foo is accessible

Implementing a method that calculates the factorial of a number, with exception

2 Answers2