Java Exceptions

• Java Exception


  An event that disrupts the normal flow of the program. It is an object which is thrown at runtime.
• Exception Handling


  A mechanism to handle errors such as ClassNotFoundException, IOException, SQLException, RemoteException, etc.
• Advantage of Exception Handling

  • The core advantage is to maintain the normal flow of the application.
• Checked Exception


  Checked at compile-time, can be recognized by the compiler, e.g. IOException, SQLException
• Unchecked Exception


  Checked at runtime, not recognized by the compiler, e.g. ArithmeticException, NullPointerException
• Error

  This is considered as an unchecked exception
• Java catch block


  Used to handle the Exception by declaring the type of exception within the parameter
• Java Multi-catch block


  A try block can be followed by one or more catch blocks, each containing a different exception handler

  
• Why use Java finally block?

  • To put "cleanup" code such as closing a file, closing connection, etc. and to place important statements to be printed regardless of the exception occurring or not.
• throw vs. throws


  throw is used to explicitly throw an exception, throws is used in the method header to indicate what exceptions the method may throw
• Java Custom Exceptions


  Also known as user-defined exceptions, derived classes of the Exception class used to customize the exception according to the user need
• NullPointerException

  Thrown when a java program process an object which contains a null value
• ArrayIndexOutOfBoundsException

  Occurs while processing an array and asking for a position that does not exist within the size of the array
• ArithmeticException

  Occurs when an exceptional arithmetic condition has occurred, this often happens when a program attempts to divide by 0
• NumberFormatException

  An unchecked exception thrown by parseXXX() methods when they are unable to convert a string to a number
• InputMismatchException

  Thrown by a Scanner to indicate the token retrieved does not match the pattern for the selected type, or that the token is out of range for the expected type
• FileNotFoundException

  References to a file that cannot be found
• IllegalArgumentsException

  Calling a method with illegal arguments
• StringIndexOutOfBoundsException

  A string index is either less than 0 or greater than or equal to the length of the string
• try

  This keyword is used to specify a block where we should place an exception code
• catch

  This keyword is used to handle the exception
• finally

  This keyword is used to execute the necessary code of the program. It is executed whether an exception is handled or not
• throw

  This word is used to throw an exception
• throws

  This keyword is used to declare exceptions. It specifies that there may occur an exception in the method
• try block

  used to enclose the code that might throw an exception
• catch block

  used to handle the exception by declaring the type of exception within the parameter