java non-static variable cannot be referenced from a static context Error

Question

The following code is generating an error on the variable con2 saying   non-static variable con2 cannot be referenced from a static context Error   I Googled for a resolution and they are suggesting the variable isn t initalized yet to make the methods available  Am I initializing this incorrectly  I also tried changing things to public but that didn t help either   import java io    import java net     import java sql    import java sql CallableStatement  import java sql ResultSet  import java sql PreparedStatement  import net sourceforge jtds jdbcx JtdsDataSource  import net sourceforge jtds jdbc Driver   class testconnect          private java sql Connection con2   null        private final String url2    jdbc jtds sqlserver           private final String serverName   SQL01        private final String portNumber    2677        private final String databaseName   App        private final String userName    bob        private final String password    boob        private final String selectMethod    cursor           private String getConnectionUrl2            System out println  initalizing jtds                String returnVal   url serverName     portNumber   databaseName   databaseName   user   userName   password   password   instance   instance                String returnVal   url2 serverName     portNumber     databaseName   user   userName   password   password            System out println  url2      returnVal             return returnVal               public static void main  String   args              con2   java sql DriverManager getConnection getConnectionUrl2                   end class

User · Answer

This is an interesting question  i just want to give another angle by adding a little more info You can understand why an exception is thrown if you see how static methods operate  These methods can manipulate either static data  local data or data that is sent to it as a parameter why  because static method can be accessed by any object  from anywhere  So  there can be security issues posed or there can be leaks of information if it can use instance variables Hence the compiler has to throw such a case out of consideration

User · Answer

Java has two kind of Variables   a   Class Level  Static          They are one per Class Say you have Student Class and defined name as static variable Now no matter how many student object you create all will have same name   Object Level         They belong to per Object If name is non-static  then all student can have different name   b  Class Level         This variables are initialized on Class load So even if no student object is created you can still access and use static name variable     Object Level        They will get initialized when you create a new object  say by new        C  Your Problem   Your class is Just loaded in JVM and you have called its main  static  method   Legally allowed  Now from that you want to call an Object varibale   Where is the object     You have to create a Object and then only you can access Object level varibales

User · Answer

You probably want to add  static  to the declaration of con2   In Java  things  both variables and methods  can be properties of the class  which means they re shared by all objects of that type   or they can be properties of the object  a different one in each object of the same class   The keyword  static  is used to indicate that something is a property of the class    Static  stuff exists all the time  The other stuff only exists after you ve created an object  and even then each individual object has its own copy of the thing  And the flip side of this is key in this case  static stuff can t access non-static stuff  because it doesn t know which object to look in  If you pass it an object reference  it can do stuff like  thingie con2   but simply saying  con2  is not allowed  because you haven t said which object s con2 is meant

User · Answer

No  actually  you must declare your con2 field static   private static java sql Connection con2   null    Edit  Correction  that won t be enough actually  you will get the same problem because your getConnection2Url method is also not static  A better solution may be to instead do the following change    public static void main  String   args          new testconnect   run          public void run          con2   java sql DriverManager getConnection getConnectionUrl2

User · Answer

Your main   method is static  but it is referencing two non-static members  con2 and getConnectionUrl2     You need to do one of three things   1  Make con2 and getConnectionUrl2   static   2  Inside main    create an instance of class testconnect and access con2 and getConnectionUrl2   off of that   3  Break out a different class to hold con2 and getConnectionUrl2   so that testconnect only has main in it   It will still need to instantiate the different class and call the methods off that   Option  3 is the best option    1 is the worst   But  you cannot access non-static members from within a static method

User · Answer

The simplest change would be something like this   public static void main  String   args  throws Exception     testconnect obj   new testconnect      obj con2   DriverManager getConnection obj getConnectionUrl2       obj con2 close

[java] java : non-static variable cannot be referenced from a static context Error

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