Java-Exceptions

• each time compiler catch a failure, it will through an exception and terminate execution
  • if didn`t catch, terminate and show error message
• each exception is in different and all class can call exception
  • useful when programmer want to check if input satisfy precondition
    • use if for case you know what is error
      • if(){ throw new exception(“error message”) }
    • use try-catch  when you don not know what might happen and program fail
      • try{   }catch(exception){print”***”; terminate/redo}
      • add finally block at the end of try-catch block
        • do no matter exception catch or not
        • finally executed
      • always do something or at least print a message and terminate the program when you catch a exception(do nothignexception is called Squelch Exceptions)
    • add throw Exception after function header when you try to throw exception in that function
    • when exception is catched, the execution is paused and check if exception is called in method it throw
      • if so, that`s where pick up
      • else, keep track the exception until catch where happened
      • continue until hit main method, if still not find, print error message and terminated
    • so if code may trigger exception, put it inside try box and use catch to catch error
      • if detected, program immediately jump to catch section and do part inside catch
• 
• code won`t check runTime exception but check others
  • try to handle with if()  bacuse it caused by programmer
  • other exception caused by compiler it will catch

 

 

• tip
  • throw early
    • throw a exception  rather than come up with imperfect fix
  • catch late
    • catch exception only if the situation can be fixed
    • otherwise, let other part throw exception rather than catch it and do nothing