Catch (exception E) in Java before 7

In Chapter 3 of the Oracle OCP Java se 8 programmer II study guide, it says as follows (page 184):

In Java 6, we can't write catch (exception E) but just throw a specific exception If we try, the compiler will still complain:

Unhandled exception type exception

What's the meaning of this? What are specific examples?

Solution

Consider the following example:

Integer add (Integer a,Integer b) {
    try {
        return a + b;
    } catch (Exception e) {
        throw e;
    }
}

Of course, adding two numbers does not throw any checked exceptions However, in Java 6, the compiler will see throw e, where e is an exception, and conclude that the method can throw any exception This requires adding a declaration that throws an exception

Starting with Java 7, what types of exceptions can the compiler solve when re - throwing e is smarter In this case, it can calculate that e can only be runtimeException (unchecked), so it is no longer necessary to add the declaration of throws exception