Reading material

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;
       }
}

Throwing 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;
       }
}

Interfaces

• Creating Interfaces
• Stack
• StackEmptyException
• Queue
• QueueEmptyException
• Deque

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. Are the following code fragments valid? If so, do they 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");
}                                 }