Define exceptions in the package in which they are thrown.

Exception Classes

• Guideline: Throw a different exception type for each abnormal condition.
• When you need to throw an exception, you can choose an already existing exception or make one of your own
  
  

  // In file TemperatureException.java
  class TemperatureException
      extends Exception {
  }
  
  // In file TooColdException.java
  class TooColdException
      extends TemperatureException {
  }
  
  // In file TooHotException.java
  class TooHotException
      extends TemperatureException {
  }
  

• Exception class should indicate the type of problem that caused the exception
• Often, exception classes may have no fields or methods
• Declare exceptions in the package they are thrown

Why Exception Classes?

• Catch clauses catch exceptions based on type
• You want each different kind of abnormal condition to be catchable in its own catch clause, to separate the handlers
• Use inheritance relationships to enable a single catch clause to catch all flavors (subclasses) of a certain kind of abnormal condition
• A catch clause for TemperatureException, for example, can catch TooHotException and TooColdException
• catch (TooHotException e) { ... has meaning