Setting outer variable from anonymous inner class

Is there any way to access caller-scoped variables from an anonymous inner class in Java?

Here's the sample code to understand what I need:

public Long getNumber(final String type, final String refNumber, final Long year) throws ServiceException {
    Long result = null;
    try {
        Session session = PersistenceHelper.getSession();
        session.doWork(new Work() {
                public void execute(Connection conn) throws SQLException {
                    CallableStatement st = conn.prepareCall("{ CALL PACKAGE.procedure(?, ?, ?, ?) }");
                    st.setString(1, type);
                    st.setString(2, refNumber);
                    st.setLong(3, year);
                    st.registerOutParameter(4, OracleTypes.NUMBER);
                    st.execute();
                    result = st.getLong(4) ;
                }
            });
    } catch (Exception e) {
        log.error(e);
    }
    return result;
}

The code is in a DAO service class. Obviously it doesn't compile, because it asks that result be final, if it is -- it doesn't compile because I try to modify a final var. I'm bound to JDK5. Other than dropping the doWork() altogether, is there a way to set the result value from within doWork()?

Solution 1:

Java doesn't know that doWork is going to be synchronous and that the stack frame that result is in will still be there. You need to alter something that isn't in the stack.

I think this would work

 final Long[] result = new Long[1];

and then

 result[0] = st.getLong(4);

in execute(). At the end, you need to return result[0];

Solution 2:

This situation arises a lot in Java, and the cleanest way to handle it is with a simple value container class. It's the same type thing as the array approach, but it's cleaner IMO.

public class ValContainer<T> {
    private T val;

    public ValContainer() {
    }

    public ValContainer(T v) {
        this.val = v;
    }

    public T getVal() {
        return val;
    }

    public void setVal(T val) {
        this.val = val;
    }
}

Solution 3:

Long is immutable. If you use a mutable class, holding a long value, you can change the value. For example:

public class Main {

public static void main( String[] args ) throws Exception {
    Main a = new Main();
    System.out.println( a.getNumber() );
}

public void doWork( Work work ) {
    work.doWork();
}


public Long getNumber() {
    final LongHolder result = new LongHolder();
    doWork( new Work() {
        public void doWork() {
            result.value = 1L;
        }
    } );
    return result.value;
}

private static class LongHolder { 
    public Long value; 
}

private static abstract class Work {
    public abstract void doWork();
}

}