抛出异常以及捕获异常？

Question

I was wondering how Java takes the following scenario

public static void main(String[] args) throws IndexOutOfBoundsException, CoordinateException, MissionException, SQLException, ParserConfigurationException {
    try {
        doSomething();
    } catch (Exception e) {
        e.printStackTrace();
    } 
}

In the above code, I am declaring the main function to throw many different exceptions, but inside the function, I am catching the generic Exception. I am wondering how java takes this internally? Ie, say doSomething() throws an IndexOutOfBounds exception, will the e.printStackTrace() get called in the last catch (Exception e) {...} block?

I know if an exception not declared in the throws area of the function gets thrown, the try/catch will handle it, but what about exceptions mentioned in the declaration?

Answer 1

In your case if ANY Exception is thrown or generated in doSomething() it will be caught in the try-catch block because of the Exception e you are catching.

Exception is the parent of all Exceptions. All Exceptions inherit from this class.

Answer 2

The catch block has greater priority over the method level throw declarations. If something would pass by that catch block, it would be thrown by the method (but that's not the case since all your mentioned exceptions are indeed inheriting from the Exception ).

If you need an exception to be handled by the catch block but forwarded further, you would have to rethrow it, eg

throw e;

Answer 3

say doSomething() throws an IndexOutOfBounds exception, will the e.printStackTrace() get called in the last catch (Exception e) {...} block?

Yes, e.printStackTrace() will be called. Because you have caught Exception which is broader than (either direct or indirect super class of ) IndexOutOfBoundException or any of the other exceptions that you have put in throws clause. But if you catch some exceptions which is narrower than IndexOutOfBoundException and other exceptions in throws clauses and any of these exceptions is encountered then throws clause will trigger.

Answer 4

Suppose you have this code:

   try{
        doSomething();
    }catch(Exception ex){
        System.out.println("Exception:");
        ex.printStackTrace();
    }catch(IndexOutOfBoundsException ex){
         System.out.println("IndexOutOfBoundsException :");
        ex.printStackTrace();
    }

You will get a compile error saying

Exception IndexOutIfBounds is already been caught

That's because every exceptions inherits from Exception class so the first thing that catch block catches is the Exception because IndexOutOfBounds is an Exception so not needed to catch it twice one for the first and one for the second.
In one case the throws will do its work when you don't declare an exception class after throws or in the try-catch.

Answer 5

The exceptions, mentioned in the declaration, is to allow a method further up the call stack to handle it. In your case these exceptions, if your main method throws them, will get handled by runtime.

Source http://docs.oracle.com/javase/tutorial/essential/exceptions/declaring.html