Question

I am getting this error when i use a string array
java.lang.NullPointerException

The code i used is as follows..

 String[] list = null;  
 String sql = "SELECT * FROM pos_products";  
 ResultSet rs = mysql_query.execute_mysql(variables.con.conn, sql);  
 while (rs.next()) {  
     System.out.println(rs.getString("product_name"));  
     list[i] = rs.getString("product_name");  
     i++;  
 }

I have to add one more thing after seeign this replies.. First thank you guys for your response.. Now the problem is i am using JList and i have to add content to it.. If i use list i cant add directly. i can user either vector or a string array. what is your thoughts on that ??

Answer 1

Your list is null, thus null[i] throws NullPointerException

You should consider either initialize it as ChrisJ describes or use a List

List<String> list = new ArrayList<String>();
.... 
    list.add( rs.getString("product_name"));
....

edit

This solves two parts, your NullPointerException and the dynamic fetch of the data.

You mention you need to put this in a JList, in that case, you can still use this approach, but separate the data retrieval from the displaying code.

So, create a method list this:

 public String[] fetchOptions() { 
      List<String> list = new ArrayList<String>();
      ... db code here
      while .... etc. et 
          list.add( rs.getString("product_name"));
      ... 
      // convert it to String[] 

     return list.toArray( new String[list.size()] );
 }

And then call this method where you create your JList

String [] options = fetchOptions();
JList aList = ... use it normally