Question

Exception handling question (code included)

I need to enter an exception handling part to this code here:

import java.util.Scanner;

public class Summation{
public static void main(String[] args) throws Exception{
Scanner input=new Scanner(new java.io.File(args[0]));
int total=0;
while(input.hasNext()){
total += input.nextInt();
}
input.close();

System.out.println("Total = "+ total);
}
}

Answer 1

I've tried using this exception handling code to enter into my program stated above but it doesn't work.

Scanner sc = new Scanner(System.in);
int numberInput;
try{
System.out.print("Enter an integer: ");
numberInput = sc.nextInt(); //
} catch (InputMismatchException e){ e.printStackTrace(); }
catch(Exception ex){ ex.printStackTrace(); }

Answer 2

Looks like it works to me..
```
Scanner sc = new Scanner(System.in);
int numberInput;
try{
System.out.print("Enter an integer: ");
numberInput = sc.nextInt(); //
} catch (InputMismatchException e){ System.out.println("e 1"); e.printStackTrace(); }
catch(Exception e){ System.out.println("e 2"); e.printStackTrace(); }
```
perhaps you're confused what e.printStackTrace() does.. it prints out the error. If you remove e.printStackTrace(); it will give no error. Upon entering "go" into the keyboard with my code, "e 1" will print out followed by an error.

You can combine exception handling like this with a loop to provide input validation.

Answer 3

@woodrow73 yes i understand that it works, but what doesn't work is when i tried to incorporate the exception handling code given into the code i posted. i still don't understand that either.

Answer 4

Hint:
What is the scope of ` int total=0; ` in what you did for your code?

Answer 5

Is it the number input of int = 0?

Answer 6

No. The scope... let me see.

Answer 7

The basics of scope. In this example code:

```
a{
int x;
b{
int y;
c{
int z;
}
}
}
```

x can be used in a, b, or c because the scope of a includes everything inside it. b and c are inside a, so they are in this scope.

y can only be used in b and c. z can only be used in c. So the following code would make for errors:

```
a{
int x=0;
b{
int y=1;
c{
int z=2;
}
}
print x+y+z;
}
```
because I am trying in a to use y and z in a, but they only exist inside b and c, not a.

Answer 8

So in that example, the scope of z is the function c and only the function c. The scope of z is the funtion a, which includes b and c.

So when I ask what the scope of ` int total=0; ` is, I am asking where can you use that variable.

Answer 9

So in this case the total of int will determine based on the code explained above? Since there's int x, y, and z and that all adds up to the total, right?

Answer 10

Ah, but I can't use it outside of c because I used x. It will cause an error.

Answer 11

The way to fix the example is this:
```
a{
int x, y, z;
x=0
b{
y=1;
c{
z=2;
}
}
print x+y+z;
}
```

Because I am declaring x, y, and z in a, they can all be used anywhere!

Do you now see the problem with your try block as posted?