Exception handling

Checked exceptions, unchecked exceptions, Errors

2 Types of Exceptions

Some Exception must not arrive (unckecked exception) but other (from external) must be managed (IOException, FileNotFoundExption)

Common exception classes

Common exception classes

  • NullPointerException
  • ArithmeticException
  • ArrayIndexOutOfBoundsException
  • ClassCastException
  • ….

API java.lang.Throwable
API Class java.lang.Error
An Error is a subclass of Throwable that indicates serious problems that a reasonable application should not try to catch. Most such errors are abnormal conditions.
API Class java.lang.Exception
The class Exception and its subclasses are a form of Throwable that indicates conditions that a reasonable application might want to catch.

Exercice

1
2
3
4
5
class X {
    void doStuff() ____________ {
        throw new FileNotFoundException();
    }
}

Which are correct in place of _?

A) blank
B) throws Throwable
C) throws RuntimeException
D) throws IOException
E) throws FileNotFoundException

Responses : B, D, E
FileNotFoundException is a IOException is a Throwable

Exercice

1
2
3
4
5
6
7
8
9
10
11
class Base2 {
    void doBaseStuff() {
        System.out.println("doBaseStuff");
    }
}

class Sub2 extends Base2 {
    void doBaseStuff() {
        System.out.println("doSubStuff");
    }
}

Which are true?
A) doBaseStuff in Base2 can be marked throws Exception without causing errors
B) doBaseStuff in Base2 can be marked throws RuntimeException without causing errors
C) doBaseStuff in Sub2 can be marked throws Exception without causing errors
D) doBaseStuff in Sub2 can be marked throws RuntimeException without causing errors
E) if doBaseStuff in Base2 were marked throws Exception,
then doBaseStuff in Sub2 can be marked throws IOException without causing errors

Reponses: A, B, D as RuntimeException is a base Exception, D
Etrange a revoir

Course

Methods must manage restult but also possible failure are their level

Multi Catch Exception from Java 7

Checked Exceptions

  • “I dont’ know what to do”
  • “I can’t fix that”

  • “It’s fatal anyway”

    So it’s waste of typing

Good desing => Limit consequences of change

When implementation changes, the client is affected => Wrong Design
Encapsulation

What type of failure are acceptable ?

  • Depends on the model /abstraction
    • Payment Method : Failure can be : No Money, Card Stolen , … or Infrastructure failure

So try to Create New Exception to specify what is the error in design/model point of view (absraction) and regroup exceptions not associated to design