Rethrow exception in java

Question

I have a very simple question about re-throwing exception in Java.

Here is the code snippet:

public static void main(String[] args) throws FileNotFoundException {
    try {
        FileReader reader = new FileReader("java.pdf");
    } catch (FileNotFoundException ex) {
        throw ex;
    }
}

public static void main(String[] args) throws FileNotFoundException {        
        FileReader reader = new FileReader("java.pdf");        
}

Why do we need to re-throw ex in the first version while the second version looks more elegant? What might be the benefits and which version is preferred over the other?

Answer 1

The question is why you think you need to rethrow the exception. Did Eclipse suggest surrounding with try-catch? In practice we rarely rethrow the same exception, but very often catch one and throw another that wraps the first one, especially if the wrapper exception is unchecked. This happens whenever you have calls declaring checked exceptions, but the method you write those calls in doesn't declare those exceptions:

public int findId(String name) {
  try {
    return db.select("select id from person where name=?", name);
  } catch (SQLException e) {
    throw new RuntimeException(e);
  }
}