Slide 10.8: Checked vs unchecked exceptions (cont.)

Slide 10.7: Checked vs unchecked exceptions
Slide 10.9: A travel-agent case study
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Checked vs Unchecked Exceptions (Cont.)

Unchecked Exceptions
Unchecked exceptions are not checked at compiling time.

In Java, exceptions under Error and RuntimeException classes are unchecked exceptions, and everything else under Throwable is checked.

In C++, all exceptions are unchecked, so it is not forced by the compiler to either handle or specify the exception. It is up to the programmers to be civilized, and specify or catch the exceptions.

Consider the following Java program. It compiles well, but it throws ArithmeticException when run. The compiler allows it to compile, because ArithmeticException is an unchecked exception.

DivideByZero.java (unchecked ArithmeticException exception)

class DivideByZero { 
  public static void main( String args[ ] ) { 
    int x = Integer.parseInt( args[0] ); 
    int y = Integer.parseInt( args[1] ); 
    System.out.println( x / y );
  }
}

shell> java DivideByZero (integer) (integer)

Two comments:

Why two types?
See Unchecked Exceptions — The Controversy for details.

Should we make our exceptions checked or unchecked?
Following is the bottom line from the Java document:
- If a client can reasonably be expected to recover from an exception, make it a checked exception.
- If a client cannot do anything to recover from the exception, make it an unchecked exception.

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Slide 10.7: Checked vs unchecked exceptions
Slide 10.9: A travel-agent case study
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