Rethrowing an Exception: Why does the method compile without a throws clause?

Question

On the source code below I\'m rethrowing an Exception.
Why is it not necessary to put the throws keyword on the method\'s signature?

Answer 1

If you thorw an checked exception you need to have it in the throws list

public void retrhowChecked() throws Exception {
    try {
        throw new IOException();
    } catch(Exception e) {
        throw e;
    }
}

If you throw an unchecked exception you don't need to put it in the throws list, you can use this to pack a checked Exception inside an unchecked one to avoid breaking code that uses this method if you change the method in question in such a way that it after the change may produce a checked exception. But you have to be careful with that, checked Exception are there to be handled!

public void retrhowUnchecked() {
    try {
        throw new IOException();
    } catch(Exception e) {
        throw new RuntimeException(e);
    }
}

Read more about Exceptions here.