Exception Handling

Throwable Hierarchy

• All exceptions in Java must inherit from Throwable class.

• Error is an exception that unrecoverable e.g. JVM runs out-of-memory
• Exception is split into two categories
  • Checked exceptions - caught by compiler
  • Unchecked exceptions - inherits from RuntimeException

Chained Exception

• Throw exception back to the calling method

   // call method2; throw exceptions back to main
   public static void method1() throws Exception
   {
      try 
      { 
         method2(); 
      }
      catch (Exception exception) // exception thrown from method2
      {
         throw new Exception("Exception thrown in method1", exception);
      }
   } // end method method1

Assertions

• Helps ensure program's validity
  • Pre-condition
  • Post-condition
• Must be explicitly enabled by -ea in java CLI argument in order to throw an exception

// assert that the value is >= 0 and <= 10
assert (number >= 0 && number <= 10) : "bad number: " + number;

try-with-resources

• Introduced with Java 7
• try statement that automatically call close() on an AutoClosable object when try block execution terminates
• Used for resource de-allocation

try (ClassName theObject = new ClassName())
{
  // Do somehing
}
catch (Exception e)
{
  // Catch exception
}