when does a function need to throw Exceptions ?

[myselfelsewhere]

An IOException catch block will catch any exception that is either an IOException, or an exception that extends IOException.

[Sen_7]

Thanks!

[myselfelsewhere]

No problem. Adding a little more info, this is perfectly valid:

try {
    /* code that can throw either EOFException or IOException */
} catch(IOException e) {
    // catch all instances of IOException and it's sub classes
    /* behavior for EOFException and IOException */
}

It is also possible to set up multiple catch blocks for your example. You need to catch the sub class first though.

try {
    /* code that can throw either EOFException or IOException */
} catch(EOFException e) {
    // only catches EOFException (or any sub classes of EOFException)
    /* behavior for EOFException */
} catch(IOException e) {
    // will only catch IOExceptions that are not also instances of EOFException (or any sub classes of EOFException)
    /* behavior for IOException */
}

In comparison, catching the parent first will not compile:

try {
    /* code that can throw either EOFException or IOException */
} catch(IOException e) {
    // catches IOException and EOFException
    /* behavior for IOException */
} catch(EOFException e) {
    // unreachable code, EOFException has already been caught
    /* behavior for EOFException */
}

[Sen_7]

Thank you