Try-with-resource 'must be a variable declaration'

Question

So I am using JDBC to connect to a local host MySQL server, and when I am coding my try block to connect with the server and send a query I am getting a 'Cannot find symbol' error.

I understand that this is because the object is initialised inside the try condition and I am trying to use it from a finally condition, but I cannot initialise it outside of the try block either, as I get an error saying 'The try-with-resources resource must be a variable declaration or an expression denoting to a final or effectively final variable'

The general idea I am trying to code up is being able to close the connection to the database in the finally block regardless of whether an exception is thrown or not. The code in question is as follows (Lines with errors highlighted) :

public static String returnEmployeeName(String ID) throws ClassNotFoundException, SQLException {
    HashMap<String, String> infoHR = connectionInfoHR();

    String query = "SELECT first_name FROM employees WHERE employee_id = '" + ID + "'";

    Class.forName("com.mysql.cj.jdbc.Driver");

    Statement st;
    ResultSet rs;
    Connection con;

    try (con = DriverManager.getConnection(infoHR.get("url"), infoHR.get("uname"), infoHR.get("pass"))) {
        //Error on line above relating to not initialising the object within the statement

        st = con.createStatement();
        rs = st.executeQuery(query);

        rs.next();
        return rs.getString("first_name");

    } finally {

        st.close();
        con.close();
    }
}

Cheers in advance for any help that can be provided :)

SSK · Answer 1 · 2020-06-05T13:49:41.420

0

You need to change your code like below

 try (Connection con = DriverManager.getConnection(infoHR.get("url"), infoHR.get("uname"), infoHR.get("pass")),
              Statement st = con.createStatement()) {
        //Error on line above relating to not initialising the object within the statement

        rs = st.executeQuery(query);

        rs.next();
        return rs.getString("first_name");
    }

Java 7 – allows us to declare resources to be used in a try block with the assurance that the resources will be closed when after the execution of that block.

you can find more here https://www.baeldung.com/java-try-with-resources

edited Jun 05 '20 at 13:49

answered Jun 05 '20 at 12:16

SSK

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Why is there no need for the closing statements? – YahooYazooYapoo Jun 05 '20 at 12:17
`try-with-resources` automatically close the connection for you. That is the main function of `try-with-resources` to close all declared resources automatically. – SSK Jun 05 '20 at 12:21
you can find out more here https://mkyong.com/java/try-with-resources-example-in-jdk-7/ – SSK Jun 05 '20 at 12:23
Why aren't you applying the try-with-resources to the statement and result set as well? – Mark Rotteveel Jun 05 '20 at 12:31
You can apply for that one as well. Edited my answer to reflect the same – SSK Jun 05 '20 at 12:32
Does this mean it will close st as well even though it isn't in the statement? – YahooYazooYapoo Jun 05 '20 at 13:34
yes it will close st as well – SSK Jun 05 '20 at 13:50

score 0 · Answer 2 · edited Jun 05 '20 at 12:31

0

I think you mean to use:

    ResultSet rs;
    try (Connection con = DriverManager.getConnection(infoHR.get("url"), infoHR.get("uname"), infoHR.get("pass")); 
         Statement st = con.createStatement()) {
        //Error on line above relating to not initialising the object within the statement

        rs = st.executeQuery(query);

        rs.next();
        return rs.getString("first_name");
    }

Keep in mind that you are using try-with-resources block that closes the connection automatically. You don't need to declare the connection before and close it in the finnaly block.

edited Jun 05 '20 at 12:31

Mark Rotteveel

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answered Jun 05 '20 at 12:16

fjsv

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Why is there no need for the closing statements? – YahooYazooYapoo Jun 05 '20 at 12:17
Just edited my answer to include that part – fjsv Jun 05 '20 at 12:18
The same can be said for result sets: they to should be closed. – Mark Rotteveel Jun 05 '20 at 12:30
Does this mean it will close st as well even though it isn't in the statement? – YahooYazooYapoo Jun 05 '20 at 13:34
Everything inside `try()` and that implements `AutoCloseable` will be automatically closed. Everything else still needs to be closed in a finally block or included in the `try()` statement – fjsv Jun 05 '20 at 13:43

Try-with-resource 'must be a variable declaration'

2 Answers2