Cannot find symbol

[Eleeist]

Hello,

When I try to compile this code:

import java.sql.*;

public class Database {
    
    public Connection connectToDatabase() throws Exception {

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

        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost/mud", "x", "x");
        
        return connection;
        
    }
    
    public void getCommands(String category) throws Exception {
        
        this.connectToDatabase();
        
        Statement statement = connection.createStatement();
        ResultSet queryResult = statement.executeQuery("SELECT * FROM commands WHERE category=" + category);

        while (queryResult.next()) {
            
            String outputString = queryResult.getString("command");
            System.out.println(outputString);
        
        }
        
    }
    
}

I get compile error:

cannot find symbol
symbol  : variable connection
location: class Database
        Statement statement = connection.createStatement();

But connectToDatabase() returns variable connection, so why does it say it does not exists?

[Fubarable]

The compiler doesn't lie:


connection != Connection.

[Eleeist]

Ok, but here:

Statement statement = connection.createStatement();

connection is lowercase and connectToDatabase() also returns lowercase:

Connection connection = DriverManager.getConnection("jdbc:mysql://localhost/mud", "x", "x");         
        return connection;

I don't really get it.

[Fubarable]

The connection variable inside of the connectToDatabase method is "local" to that method. Outside of the method it is invisible (read up on variable scope for more on this).

You call connectToDatabase inside of your getCommands method, but you discard the object returned. For example you do this:

    public void getCommands(String category) throws Exception {
        this.connectToDatabase();

instead of this:

    public void getCommands(String category) throws Exception {
        Connection connection = connectToDatabase();  // the "this" is not necessary

To use the Connection object returned by that method, you'll have to assign it to a variable as I show above.

[Eleeist]

I get it now. Thanks for explanation :).

[Fubarable]

I get it now. Thanks for explanation :).

You're welcome. Glad you've got it working.