What is the meaning of this statement from a blog saying a function has to declare Throwable at method signature to catch it?

Question

I am trying to understand exception handling in Java and i keep running into variations of the below mentioned confusing statement in several articles -

There are several reasons why catching instance of java.lang.Throwable is bad idea, because in order to catch them you have to declare at your method signature e.g. public void doSomething() throws Throwable.

This is from http://javarevisited.blogspot.com/2014/02/why-catching-throwable-or-error-is-bad.html#ixzz4hQPkFktf

However, this code compiles -

class CatchThrowable
{

    void function()
    {

        try
        {
            throw new Throwable();
        }
        catch (Throwable t)
        {

        }
    }

    public static void main(String[] args)
    {

        try
        {

        }
        catch (Throwable t)
        {

        }
    }
}

Both main and function are able to catch Throwable without declaring that they throw it. My understanding is that the throws keyword is used to declare the checked exceptions which a function throws, not those which it catches. Please clarify the quoted statement.

If you catch it in the method, then the method doesn't throw it *outside*. Capiche? — Kayaman, May 18 '17 at 11:29
yes, i think the tutorial meant the method that will throw the exception should have `throws Exception` in it's signature — Yazan, May 18 '17 at 11:30
I don't think the blog makes this very clear. Related: http://stackoverflow.com/questions/6083248/is-it-a-bad-practice-to-catch-throwable — Steve Smith, May 18 '17 at 11:34

score 1 · Answer 1 · answered May 18 '17 at 11:30

The statement:

order to catch them you have to declare at your method signature e.g. public void doSomething() throws Throwable.

is basically wrong.

You just have to understand the following. There is a exception Hierarchy A method can throw all types of exception, it just depends on your needs which one you catch and which one not.

It is also not a good idea to catch Error (which includes that you should also not catch Throwable) because there are some severe JMV-VirtualMachineError's like OutOfMemoryError which you usually not should catch.

But this has nothing to do which the fact, what a method declares in its throws part.

What is the meaning of this statement from a blog saying a function has to declare Throwable at method signature to catch it?

1 Answers1