Reading material

(1st) Pages 704-707 (section on exceptions)

(2nd) Pages 76-80 (section on exceptions)

Additional material

• Handling Errors with Exceptions (rest of the chapter)
• ImprovedFibonacci.java
• ExceptionCreator.java
• MyException.java

public static void fibonacci(String[] args)
{
       try
       {
              int lo = 1;
              int hi = 1;
              int n = Integer.parseInt(args[0]);
              System.out.println(lo);
              for (int i = 1; i < n; i++)
              {
                    System.out.println(hi);
                    int temp = hi;
                    hi = lo + hi;
                    lo = temp;
              }
        }
        catch (ArrayIndexOutOfBoundsException e)
        {
              System.err.println("No command line argument provided");
        }
        catch (NumberFormatException e)
        {
              System.err.println("Command line argument " + e.getMessage() + " is not an integer");
        }
        finally
        {
              System.out.println("Done!");
        }
}

Specifying exceptions

public static void fibonacci(String[] args) throws ArrayIndexOutOfBoundsException, NumberFormatException
{
       int lo = 1;
       int hi = 1;
       int n = Integer.parseInt(args[0]);
       System.out.println(lo);
       for (int i = 1; i < n; i++)
       {
             System.out.println(hi);
             int temp = hi;
             hi = lo + hi;
             lo = temp;
       }
}

Throwning exceptions

public static void fibonacci(String[] args) throws ArrayIndexOutOfBoundsException, NumberFormatException
{
       int lo = 1;
       int hi = 1;
       if (args.length == 0)
       {
             throw new ArrayIndexOutOfBoundsException();
       }
       int n = Integer.parseInt(args[0]);     // may still throw a NumberFormatException
       System.out.println(lo);
       for (int i = 1; i < n; i++)
       {
             System.out.println(hi);
             int temp = hi;
             hi = lo + hi;
             lo = temp;
       }
}

Question

AException and BException are both subclasses of Exception. Furthermore, BException is a subclass of AException. Draw the inheritance diagram. Is an AException object of type BException? Is a BException object of type AException? method may throw exceptions of type AException and BException. Do the following code fragments always produce the same output?

try                               try
{                                 {
    method();                         method();
}                                 }
catch (AException e)              catch (BException e)
{                                 {
    System.out.println("A");          System.out.println("B");
}                                 }
catch (BException e)              catch (AException e)
{                                 {
    System.out.println("B");          System.out.println("A");
}                                 }