Java7 multiple exception handling

Question

I have been trying to find out answer to this question but did not get any satisfactory explanation. Here is some background:

Java 7 allows us to catch multiple exceptions in a single catch block provided those exceptions are from diffrent hierarchy. Eg:

try {
    // some code

} catch(SQLException | FileNotFoundException e) {
    e.printStackTrace();
} catch(Exception e) {
    e.printStackTrace();
}

But if exceptions are from the same hierarchy we must use multiple catch blocks like:

try {
    // some code
} catch(FileNotFoundException  e) {
    e.printStackTrace();
} catch(IOException e) {
    e.printStackTrace();
}

But if I try to write code like below compiler complains that "The exception FileNotFoundException is already caught by the alternative IOException"

try {
    // some code
} catch(FileNotFoundException | IOException  e) { // compiler error
    e.printStackTrace();
}

Now my question is: Why compiler reports an error in last case, can't it figure out that FileNotFoundException is special case of IOException? This would save code duplication when my exception handling logic is same.

Answer 1

Why compiler reports an error in last case, can't it figure out that FileNotFoundException is special case of IOException?

Because FileNotFoundException is a subclass of IOException. In other words, the "FileNotFoundException |" part is redundant.

The reason why the code below is ok...

} catch(FileNotFoundException  e) {
    ...
} catch(IOException e) {
    ...
}

...is because here the IOException clause matters: If a SocketException is thrown for instance, it will pass the by the FileNotFoundException part, and get caught in the IOException clause.