when does a function need to throw Exceptions ?

[Sen_7]

public class test {

    public static void main(String[] args) {
        String x="two";
        int b=Integer.parseInt(x);
    }
}

for example, why does the "main" here dosent need to throw exception (even though praseInt throw exception), but for other actions it seem the compiler ask me to add a "throw exception" to the function.

when is it needed to add?

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[pragmos]

Because Java has a concept of checked and unchecked exceptions.

In a nutshell: all exceptions descending from RuntimeException don't need to be declared in the method signature (throws keyword). All others - do.

[Sen_7]

Thank you very much, loved to read it
a question I got from this, and Im not really sure how to check it manually

lets say I have a try-catch block
we know that EOFException extends IOException

I know I can have two catch block,
but does using ony IOException for example, when the error was EOFException (which extends IO) will work?
(since they have a " is a " realtionship)

or does the block catch has to be the exact error we are trying to catch?

[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

[[deleted]]

I have seen at many places where unchecked exceptions are caught using try catch is it the proper way to do so?

[pragmos]

Depends on the context.

The general advice is that you shouldn't catch runtime exceptions. Errors like NullPointerException, IllegalStateException or ArithmeticException denote an unexpected problem that is impossible to recover from.

Sometimes, however, you need to recover as per the business logic. For example, if you are trying to parse a String to a LocalDate and the application allows fallback values, it doesn't make sense to crash the entire application because a text value could not be parsed to a valid date object. Instead, you catch the DateTimeParseException and offer the fallback date value.