Question

I have a variable that is not supposed to change its value after it’s been initialized, so I want to define it as a final variable.

the problem is that the variable has to be initialized inside a try block, so I get the following troubles:

I have the following code:

Connection conn = null;
try {
    conn = getConn(prefix);
    [...do some stuff with conn...]
} catch (Exception e) {
    throw new DbHelperException("error opening connection", e);
} finally {
    closeConnection(conn);
}

If I declare the variabale as final, without initializing it to null, I get a ‘The local variable conn may not have been initialized’ on the finally block. On the other hand, if I declare it final and initialize it to null, I get the error ‘The final local variable conn cannot be assigned’ in the try block.

EDIT: after lxx answer, I came with this version

try {
    final Connection conn = conn = getConn(prefix);
    try {
        return selectAll(conn, sql, params);
    } catch (Exception e) {
        throw new DbHelperException("error executing query", e);
    } finally {
        closeConnection(conn);  
    }
} catch (Exception e) {
    throw new DbHelperException("error opening connection", e);
}

So this should be the way to do it?

—

Lesson learned:

I think that the correct answer to the question is the one that lxx gave, but in this case I guess that the cons of declaring the variable final outweights it’s benefits…

—

EDIT: found two questions on stack overflow about when to use final

When should one use final for method parameters and local variables?

Using "final" modifier whenever applicable in java

Answer 1

You could handle the Exceptions more accurately. If you get an Exception opening the connection, you don’t have to close it in the finally block I guess. If you get an exception after that, in the try block, and handle the exception in a new nested try-catch block you don’t need to define the variable outside. Something like:

    try {
        final Connection conn = getConn(prefix);
        try {
            //code using conn
        } catch (Exception e) {

        } finally {
            closeConnection(conn);
        }
    } catch (DbHelperException e) {
        throw new DbHelperException("error opening connection", e);
    }