为什么不从SQLite数据库获取数据？

Question

I am trying to connect to a database located in my project directory and get data from it, but is give Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException error.

Here is my code:

public static Connection ConnectDB(){
        Connection conn = null;
        Statement stmt = null;
        try{
            Class.forName("org.sqlite.JDBC");
            conn = DriverManager.getConnection("jdbc:sqlite:database01s.sqlite");
            JOptionPane.showMessageDialog(null, "Connected");

        conn.setAutoCommit(false);
        System.out.println("Opened database successfully");

        ResultSet rs = stmt.executeQuery( "SELECT id FROM DAN" );

        while(rs.next()){
            System.out.println( rs.getInt("id") );
        }

        rs.close();
        stmt.close();
        conn.close();

    }catch(ClassNotFoundException | SQLException | HeadlessException e){
        JOptionPane.showMessageDialog(null, e);
        System.err.println( e.getClass().getName() + ": " + e.getMessage() );
        System.exit(0);
    }
    return null;
}

It does connect successfully, but it gives error when it reaches this line: ResultSet rs = stmt.executeQuery( "SELECT id FROM dan" );

And this is a picture of my database to to see if I am entering the right table and info:

Answer 1

You are getting a null pointer exception because stmt is equal to null, and you are calling executeQuery() on it. You can't call methods on a null object.