Load database values to Vector

Question

we have a database and in this database there is one table "content" and 3 columns "id", "movie_name", "movie_category".

We want to load this values to Vector and show it but there is a problem that we just get "null" value.

How can we fix this ?

import java.sql.Connection;  
import java.sql.DriverManager;  
import java.sql.ResultSet;  
import java.sql.Statement; 
import java.util.*;
import java.awt.*;
import javax.swing.*;

public class Data extends JPanel{

         Connection connection = null;  
         ResultSet resultSet = null;  
         Statement statement = null;  

         static Vector<Vector<String>> data = new Vector<Vector<String>>();
         public String vString;

         public String database(){
             try 
             {  
                 Class.forName("org.sqlite.JDBC");  
                 connection = DriverManager.getConnection("jdbc:sqlite:src//movies.db");  
                 statement = connection.createStatement();  
                 resultSet = statement.executeQuery("SELECT id, movie_name, movie_category FROM content");

                 Vector<String> columnNames = new Vector<String>();
                 columnNames.add("id");
                 columnNames.add("movie_name");
                 columnNames.add("movie_category");

                 while (resultSet.next()) 
                 {  
                     Vector<String> vString = new Vector<String>();

                     vString.addElement(resultSet.getString("id"));
                     vString.addElement(resultSet.getString("movie_name"));
                     vString.addElement(resultSet.getString("movie_category"));


                     data.add(vString);




                 }  
             } //try
             catch (Exception e) 
             {  
                 e.printStackTrace();  
             }
             finally 
             {  
                 try 
                 {  
                     resultSet.close();  
                     statement.close();  
                     connection.close();  
                 } 
                 catch (Exception e) 
                 {  
                     e.printStackTrace();  
                 }  
             }
            return vString;  
         }


public static void main(String[] args) {


    Data d = new Data();
    System.out.print(d.database());

}

}

Please post the **relevant** part of the code here. – Mureinik Dec 20 '14 at 15:39 — Mureinik, Dec 20 '14 at 15:39
for good understanding i post whole of the code – Burak Kurt Dec 20 '14 at 15:43 — Burak Kurt, Dec 20 '14 at 15:43

Lukas Risko · Accepted Answer · 2014-12-20T16:12:30.637

Problem is you declared instance variable vString but you never assign anything to it, so it stays (auto)initialized with null. Inside the while loop you declare a local varibale vString and it is used for storing data retrieved from database. After while loop ends, local varibale vString is not more. In main method you print the result of database() method what is null stored in the instance variable vString. Your problem is known as Variable shadowing.

Change System.out.print(d.database()) to System.out.print(d.data)
Delete declaration public String vString
Make database() method return void

Repaired code:

public class Data extends JPanel{

     Connection connection = null;  
     ResultSet resultSet = null;  
     Statement statement = null;  

     static Vector<Vector<String>> data = new Vector<Vector<String>>();

     public void database(){
         try 
         {  
             Class.forName("org.sqlite.JDBC");  
             connection = DriverManager.getConnection("jdbc:sqlite:src//movies.db");  
             statement = connection.createStatement();  
             resultSet = statement.executeQuery("SELECT id, movie_name, movie_category FROM content");

             Vector<String> columnNames = new Vector<String>();
             columnNames.add("id");
             columnNames.add("movie_name");
             columnNames.add("movie_category");

             while (resultSet.next()) 
             {  
                 Vector<String> vString = new Vector<String>();

                 vString.addElement(resultSet.getString("id"));
                 vString.addElement(resultSet.getString("movie_name"));
                 vString.addElement(resultSet.getString("movie_category"));

                 data.add(vString);
             }  
         } //try
         catch (Exception e) 
         {  
             e.printStackTrace();  
         }
         finally 
         {  
             try 
             {  
                 resultSet.close();  
                 statement.close();  
                 connection.close();  
             } 
             catch (Exception e) 
             {  
                 e.printStackTrace();  
             }  
         }
     }


public static void main(String[] args) {
    Data d = new Data();
    d.database();
    System.out.print(d.data);
}

we delete the outer vString but when we try to return inner vString it is also occurs a problem. can you modify that part of the code ? — Burak Kurt, Dec 20 '14 at 15:55
i changed System.out.print(d.data()); with System.out.print(d.data); because there is no data() method but i still get the same result — Burak Kurt, Dec 20 '14 at 16:01
yes i have a sqlite database named "movies.db" and it has values in it — Burak Kurt, Dec 20 '14 at 16:09
i trieed to add a value to vector manually vString.addElement("a"); it still shows [] as a result — Burak Kurt, Dec 20 '14 at 16:12
You're welcome. And for the future consider using `ArrayList` instead of `Vector` ([differences-between-arraylist-and-vector](http://stackoverflow.com/questions/2986296/what-are-the-differences-between-arraylist-and-vector)) — Lukas Risko, Dec 20 '14 at 16:17
it is my homework and my teacher told us "i strongly suggest you using vector" that is why i try to use vector — Burak Kurt, Dec 20 '14 at 16:21

Load database values to Vector

1 Answers1