Exceptions

• Throwable superclass
• Throwable is parent van Exception en Error

• Exception is parent van RuntimeException

• RuntimeException kan altijd gegooid worden. De andere Exceptions moeten worden gechecked

• Exception hoeft niet bad te zijn
• checked exception => CHECKED by the compiler

• unchecked exception => NOTCHECKED by the compiler

• Bij overriding methods only same or less exceptions NOT more exceptions

Throwable
  Exception
    RuntimeException

  Error
    OutOfMemoryError
    StackOverflowError

exceptions


Exception Types

• Throwable
• Exception
• Error

Checked Exceptions

• must be declared or handled by the application where it is thrown
• checked exception inherit Exception but not RuntimeException
• try catch blocks
• handle or declare rule

Unchecked Exceptions

• checked exceptions
• unchecked exceptions (Runtime exceptions)
• unchecked do not need to be declared or handled where it is thrown. RuntimeExceptions or Error
• unexpected but not fatal.

throws and throw

Recognizing Exception Classes

• RuntimeException
• checked Exception (oplossen!)
• Error

RuntimeException e  = new RuntimeException();
throw e;
Exception e  = new Exception(); 
throw e; // DNC

public class MyRuntimeException extends RuntimeException {

    public MyRuntimeException() {
        super("My runtime exception");
    }
}

public static void main(String[] args) {
        MyCheckedException e = new MyCheckedException(); // DNC
        throw e; //DNC
    }

Checked exception - program continues na catch

RuntimeException - continues in try catch - stops als niet in try catch

Error stopt altijd

Recognizing Exception CLasses

• ArithmeticException - Thrown when code attempts to divide by zero
• ArrayOutOfBoundsException - array en illegal index
• ClassCastException - illegal cast to another class
• NullPointerException - when there is a null reference when object is required..
• IllegalArgumentException - method input illegal (handig als guard met specifieke error)
• NumberFormatException - "123abc" is een string die niet naar nummer kan SUBCLASS van IllegalArgumentException

ClassCastException

let op:

String s = "sdf";
        Object o = s;
        Integer i = (Integer) o;
// bouwt wel maar runtime error

String s = "sdf";
Integer i = (Integer) s; // bouwt niet.

Checked Exceptions Classes

• IOException while reading/writing file
• FileNotFoundException subclass of IOException

Error Classes

• ExceptionInInitializerError static init throws
• StackOverflowError endless loop in memry
• NoClassDeffoundError

Handling Exceptions

• eerst subclass dan parent anders unreachable code => DNC
• multicatch met | => catch( exception1 | exception2 error) {}
• multicatch met 1x error variable!
• multicatch niet met sub and parent classes DNC
• exception kan maar in 1 catch voorkomen
• catch niet verplicht kan maar moet niet

Finally

• als geen catch dan finally
• finally will always run!
• finally kan zonder catch
• allen System.exit(0); kan finally doen ontlopen
• finally is handig om resources af te knopen

Closing resources

• try-with-resources statement or automatically cloase all resources openend in a try clause.
• mag catch en finnally overslaan
• implicit finally runs FIRST
• 1x finally is max
• declaring multiple resources gescheiden door ;

Scope of try-with-resources

• Scope is alleen in de try. Niet catch en finally....
• resources are closed after try en before catch&finally
• resource closed in reveoerse order of creation

Declaring and Overriding Methods with exceptions

• minder CHECKED exceptions mag in child NIET in parent
• child mag ook child van exception
• unchecked exception mag minder of meer in childs en parents

printing exceptions

• sout(e)
• sout(e.message())
• e.printStackTrace()

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