Chapter 6

Chapter 6

1. Exceptions

   • Event that alter program flow
   • Throwable supperclass
     • for all objects
     • java.lang.Throwable
       • java.lang.Exception(Checked Exceptions)
         • java.lang.RuntimeException (Unchecked Exceptions)
       • java.lang.Error
   • Error
     • something went wrong and your program should not attempt to recover from it.
       • Not okay for program to catch
       • No required to handle or declare
   • Exception(Checked)
     • Java requires code to
       • handle them
       • declare them in method
     • Okay to catch
   • RuntimeException(Unchecked)
     • unexpected but not necessarily fatal
       • Okay to catch
       • No required to handle or declare
   • keywords
     • throw
       • Tells Java to throw an exception
     • throws
       • might throw an exception

2. Try Statement

   • Java use it to separate the logic
     • might throw an exception
       • from the logic to handle that exception.
   • Syntax
     • Try Block
       • If doesn't throw an exception
         • catch block doesn't run
       • Needs:
         • to have a catch or finally block
     • Catch Block
       • Exception handler
       • catch exception type must match the try exception error
       • must have a parenthesis
         • (exception_type identifier)
     • Finally Block
       • finally must be after a catch block
         • not viceversa
       • Run code at the end of the statement
         • Always executes whether or not an exception occurs
           • except if System.exit(0)
   • When a superclass is caught before a subclass
     • compiler error unreachable code

3. Common Exception Types

   • Runtime Exceptions
     • thrown by JVM
       • ArithmeticException
         • when code attempt to divide by zero
       • ArrayIndexOutOfBoundsException
         • when code uses an illegal index to access an array
       • ClassCastException
         • when cast an exception to a subclass of which it is not an instance
     • thrown by programmer
       • IllegalArgumentException
         • indicate that a method has been passed an illegal argument
       • NullPointerException
         • when there is a null reference when an object is required
       • NumberFormatException
         • when try to convert a string to a numeric type and the string doesn't have an appropiate format
   • Checked Exceptions
     • thrown programmatically
       • IOException
         • when there's a problem reading or writing a file.
       • FileNotFoundException
         • when trying to reference an unexisting file
         • subclass of IOException
   • Errors
     • thrown by JVM
       • ExceptionInInitializerError
         • when static initializer throws an Exception and doesn't handle it
       • StackOverflowError
         • when a method calls itself to many times
       • NoClassDefFoundError
         • when a class code is available at compile time but not at runtime