CODEWITHSUNDEEP
javaexceptionmulti-catch
Ishan Saini
Ishan Saini

Reputation: 31

Unable to resolve exception class in Multi catch

I am creating a custom exception class using multicatch(Java 7 and above). This is the class that I have created. Please refer to the following code: 

public class CustomException extends Exception{

public CustomException() {
    System.out.println("Default Constructor");
}
public CustomException(ArithmeticException e, int num){
    System.out.println("Divison by ZERO! is attempted!!! Not defined.");
}
public CustomException(ArrayIndexOutOfBoundsException e, int num){
    System.out.println("Array Overflow!!!");
}
public CustomException(Exception e, int num){
    System.out.println("Error");
}

and the above class is extended by the following class. 

import java.util.Scanner;

public class ImplementCustomException extends CustomException {

public static void main(String[] args) throws CustomException {
    int num = 0;
    System.out.println("Enter a number: ");
    try(Scanner in = new Scanner(System.in);){

        num = in.nextInt();
        int a = 35/num;

        int c[] = { 1 };
        c[42] = 99;
    }
    catch(ArithmeticException|ArrayIndexOutOfBoundsException e){

        throw new CustomException(e, num);
    }
}
}

Every time I am trying to run this, it calls the same constructor which is the one with "Exception". Why is that happening?

However, if I replace the multi-catch syntax with the following code. It is working as expected.

catch(ArithmeticException ex){
        CustomException e = new CustomException(ex, num);
        throw e;
}
catch(ArrayIndexOutOfBoundsException ex){
        CustomException e = new CustomException(ex, num);
        throw e;
}

Please assist me with the possible changes that I can make in order to use multi catch and make it throw the required exception.

Upvotes: 1

Views: 516

Answers (2)

glglgl
glglgl

Reputation: 91129

There is no common parent to ArithmeticException and ArrayIndexOutOfBoundsException other than Exception. In this one block

catch(ArithmeticException|ArrayIndexOutOfBoundsException e){
    throw new CustomException(e, num);
}

e gets a static type, and this is ExceptionRuntimeException. With this, the CustomException(Exception e, int num) is called.

If you split them up, e has a more dedicated type.

Upvotes: 4

Andy Turner
Andy Turner

Reputation: 140514

The behaviour is defined in JLS Sec 14.20 via this not-very-prominent sentence:

The declared type of an exception parameter that denotes its type as a union with alternatives D1 | D2 | ... | Dn is lub(D1, D2, ..., Dn).

lub means "least upper bound", defined in JLS Sec 4.10.4:

The least upper bound, or "lub", of a set of reference types is a shared supertype that is more specific than any other shared supertype (that is, no other shared supertype is a subtype of the least upper bound).

In your case, the lub of ArithmeticException and ArrayIndexOutOfBoundsException is RuntimeException, so the overload taking Exception as a parameter type is the most specific method that can be called.

Remember that it is the compiler that decides on the overload to be called: it is not decided at runtime.

Upvotes: 3

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