Exception Handling

1
Exception Handling

• Chapter 10

2
Exceptions Handling

• Allows a programmer to catch abnormal condition
  that arise in a code sequence
• Keywords
• try
• catch
• throw
• throws
• finally

3
Exception Types

• Run-time Exceptions
• Exceptions that can be handled by your programs
• Checked Exceptions
• Always required to catch
• Unchecked Exceptions
• Dont need to be handled by the programmer (an
  option)

• Errors
• Can not be handled by the programs
• Out of the programmers control

4
try and catch

• try
• Used to enclose a block of code where an
  exception can take place
• catch
• Will jump to this area of code if a particular
  type of exception needs to be handled

5
An Example

• class Test
• public static void main (String args )
• int a 0
• try
• a 84 / (math.Random( ) 7)
• System.out.println(When will this line be
  skipped?)
• catch (ArithmeticException e)
• System.out.println(Division by zero.)
• a 0

6
Multiple catch clauses

• class Test
• .
• .
• try
• .
• catch (ArithmeticException e)
• catch (IOException e)
• catch (Exception e)

7
Nested try statements

• class Test
• .
• .
• try
• .
• try //NESTED if exception is not handled
  here
• catch // it will go up to the next
  exception try to find
• // the next place to handle the exception
• catch (ArithmeticException e)
• catch (Exception e)

8
Throw

• Allows the programmer to handle the exception
  within the area and then sends it up to the next
  level to handle the exception
• try
• catch (IOException e)
• //write code handle exception
• Throws e // pass it along

9
Throws

• Keyword that allows other components of the
  program know that this code can throw an
  exception and it is not handled within the block
  of code
• ..
• class Test
• public static void main(String args) throws
  IOException
• BufferedReader in new BufferedReader(new
  InputReader(System.in))

10
finally

• Keyword that is used to designate a block of code
  that should be executed whether there was an
  exception or there was no exception
• try
• .
• catch (ArithmeticException e)
• finally
• //code will always be

11
Creating your own exceptions

• Subclass Throwable
• class yourClass extends Throwable
• .
• Exception would be called yourClass
• Table 10-3.