Non-static ThreadLocal variables

I want to know what is the actual problem in having non-static ThreadLocal variables ? I am looking for some insights. Java doc says that typically ThreadLocal variables are private and static but does not mention that it has to be mandatorily static and does not provide the reason behind the recommendation for being static. Can anyone please clarify ?

What if I have a code like this i.e. a singleton object having reference to a non-static ThreadLocal variable ?
public class ThreadLocalTest {
     private ThreadLocal<Integer> tlocal;
     private static final ThreadLocalTest tester = new ThreadLocalTest();
     private ThreadLocalTest() {
          this.tlocal = new ThreadLocal<Integer>();
          log("Created ThreadLocalTest instance");
     public static ThreadLocalTest getInstance() {
          return tester;
     public void setValue(int i) {
          this.tlocal.set(new Integer(i));
          log("Set value = " + i);
     public int getValue() {
          int i = this.tlocal.get();
          log("Got value = " + i);
          return i;
     public static void main(String[] args) {
          for(int i = 0; i < 2; i++) {               
               Thread t = new Thread(new Runner());
               t.setName("Thread-" + i);               
               t.start();
     public static void log(String msg) {
          String thread = Thread.currentThread().getName();
          String date = new java.util.Date().toString();
          String prefix = "[" + thread + "] " + date + ": ";
          System.out.println(prefix + msg);
     static class Runner implements Runnable {          
          public void run() {
               for (int i = 0; i < 100; i++) {
                    ThreadLocalTest tester = ThreadLocalTest.getInstance();
                    tester.setValue(i);
                    tester.getValue();
Edited by: radiatejava on Oct 22, 2012 4:56 PM

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                        Calendar cal     =Calendar.getInstance();
                        year               =cal.get(cal.YEAR);
                        month               =cal.get(cal.MONTH) + 1;
                        date               =cal.get(cal.DATE);
                        hour               =cal.get(cal.HOUR_OF_DAY);
                        min                    =cal.get(cal.MINUTE);
                        week               =cal.get(cal.DAY_OF_WEEK);
                        access_date          =(month*100)+date;
                        access_time          =(hour*100)+min;
                        if(access_date<1000)
                             str_date="0"+new Integer(access_date).toString();
                        else
                             str_date=new Integer(access_date).toString();
                        if(access_time<100)
                             str_time="0"+new Integer(access_time).toString();
                        else
                             str_time="0"+new Integer(access_time).toString();
                   }catch(Exception e){
                        //System.out.print("Exc"+e.getMessage());
                        //return false;
                   finally{
                             if(rs!=null){
                                  try{     rs.close();}catch(Exception e){}
                             if(rs2!=null){
                                  try{     rs2.close();}catch(Exception e){}
                             if (stmt!=null){
                                  try{     stmt.close();}catch(Exception e){}
                             //if (conn!=null){
                                  try{     conn.close(); }catch(Exception e){}
                        //return back;
    /*     public static void main(String[] args)
              System.out.println("Hello World!");

    Hello jjaekim,
    if rs is a class variable (the same value for all objects),
    try this (more likely to be the right solution) :
    static ResultSet rs;
    instead of :
    ResultSet rs;
    if rs has a different values in different objects,
    then you should add the object name when using it like this :
    myObject.rs or this.rs

  • Another question: non-static variable super cannot be referenced from ...?

    class a
    int i;     
    int j=2;
    a(int i)
    this.i=i;
    public class b extends a
         b()
         super(8);     
    public static void main(String args[])
    b test=new b();
    System.out.print(test.i);
    test.j=1;
    System.out.print("test.j="+test.j);
    System.out.print("super.j="+super.j);
    b.java:28: non-static variable super cannot be referenced from a static context
    System.out.print("super.j="+super.j);
    ^
    1 error
    thanks

    You cannot call "super" from a static context. Just like you can't use "this" or call any non-static methods in a static context.
    Try with test.super.j, although I'm not sure if it works. But you can call super.j in a non-static context, e.g. in your constructor, or in a non-static method.

  • "non-static variable cannot be referenced from a static contex"

    Hi, i'm writing a booking program at school and i'm getting 27 "non-static variable cannot be referenced from a static contex" errors. I can't find anything wrong with the code so I'm just asking you guys to look it through..
    public class bokningsmeny
    Bokning[] bokningslista = new Bokning[1000];
    String fornamn;
    String efternamn;
    String civilstand;
    String adress;
    String personnr;
    String telefonnr;
    int regnr;
    double inkomst;
    public static void main(String[] args)
    for(;;)
    System.out.println("\nMeny");
    System.out.println("________\n");
    System.out.println("1. Mata in nya personer.");
    System.out.println("2. S&ouml;k personen via personnummer och skriv personens andra uppgifter.");
    System.out.println("3. S&ouml;k personen via efternamn och skriv personens andra uppgifter.");
    System.out.println("4. S&ouml;k personen via personnummer och &auml;ndra adress.");
    System.out.println("5. S&ouml;k personen via personnummer och &auml;ndra telefonnummer.");
    System.out.println("6. S&ouml;k personen via personnummer och &auml;ndra civilst&aring;nd.");
    System.out.println("7. S&ouml;k personen vis personnummer och &auml;ndra inkomst");
    System.out.println("8. Skriv ut alla personer med givet namn.");
    System.out.println("9. Skriv ut alla personer med givet efternamn");
    System.out.println("10. Skriv ut alla personer med given adress");
    System.out.println("11. Skriv ut hela listan");
    System.out.println("12. Avsluta\n");
    int menyval = Keyboard.readInt();
    System.out.println("\n");
    switch(menyval)
    case 1:
    System.out.println("Mata in nya personer.\n______________________\n");
    boolean BOOuppgifter = false;
    for(int i = 0; i <= 1000; i++)
    if(bokningslista +== null)+
    +{+
    +SkrivInUppgifter();+
    +System.out.println("\nSt&auml;mmer informationen? (Y/N)");+
    +boolean BOOcase1yesorno = IsInputCorrect();+
    +if(BOOcase1yesorno == true)+
    +{+
    +System.out.println("\nBokningen lyckades!\n");+
    +bokningslista += new Bokning(fornamn, efternamn, civilstand, adress, personnr, telefonnr, regnr, inkomst);
    ++++else if(BOOcase1yesorno == false
    ++++System.out.println("\nBokningen avbruten.\n")
    ++++break
    ++++++break
    ++++case 2
    ++++System.out.println("Sok person med personnummer och &auml;ndra uppgifter.")
    ++System.out.println("___________________________________________________________\n")
    ++System.out.print("Skriv in sokord: ")
    ++String query = Keyboard.readString()
    ++query = query.toUpperCase()
    ++String personnummersok
    ++boolean contains
    ++int antal = 0
    ++boolean BOOcase2result = false
    ++System.out.println("Resultat: \n_________\n")
    ++for(int i = 0; i < 1000; i++
    ++++if(bokningslista +!<b<br />+<em<b<br />+++personnummersok = (bokningslista+.hamtaPersonnum()).t
    ++++contains = personnummersok.con
    ++++if(cont
    +<<br />++++BOOcase2r
    ++++ant
    ++++fornamn = bokningslist
    +++++efternamn = boknin
    ++++++personnr
    +++++++System.out.println(antal + ". " + fornam
    ++++<e<br />+++++++System.out.pri<br<br />+++++<em<br />+++++++System.out.println("\nVilket sokresultat vill du v&bdquo
    ++++<<br />+++++++if(case2ch
    +++++++System.ou
    +++<e<<br />+++<em<br />++++
    ++<em<br />+++++++System.out.p
    +++++<e<br />+++<<br<br /<br />+++++++System.out.printl
    +++<em<br />+++++<em<br />++
    <e<br />++++++++Sy
    +++++
    ++++++<e<br /><em<br />++++++++<<br />+++++<e<br />+++
    +++<<br />+++++++++else if(case11exit != 'y' &<br<br />+<<br />++++
    ++++
    +++++
    ++++<e<br />+++++++
    ++++<em<br />+++++
    +++<em<br />+++++<em<br />++++<<br />++++++
    ++++<e<br />+++++++<e<br />++<em<br />++++<e<br />+++<<br />+++++++++System.out.println("\n\nNamn: " + fornamn + "
    ++++++++++ "\nHemadress: " + adr
    ++++++++++ telefon
    +<<br />+++++++++Syste
    ++++<em<br />+++++++++if(correct
    <em<br />++<em<br />++<<br />++++<e<br /><<<br /><e<br />+++++++++I have another file with the Bokning.java class in it but I know for sure that its error free. Notice that I'm not nearly done with the program, theres like 10 more 'cases' to be created but I dont w
    ++<em</p>                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       

    Your code goes "+" crazy there, but here is your problem:
    public class B extends A {
        public void method() {}
        public static void main(String[] args) {
            //method(); //non-static method method() cannot be referenced from a static context
            B b = new B();
            b.method();
    }You need to be clear about the difference between static methods and non-static (instance) methods. Instance methods are applied to objects.

  • Non static variable?

    i've a small problem with an object.
    public class klassenobjekttest
    public static void main(String[] args)
    Auto meinFahrzeug;
    meinFahrzeug = new Auto();
    meinFahrzeug.name = "Porsche";
    meinFahrzeug.erstzulassung = 1933; // woher soll ich das wissen?
    meinFahrzeug.leistung = 300;
    System.out.println("Fahrzeug name: " + meinFahrzeug.name);
    System.out.println("Fahrzeug Erstzulassung: " + meinFahrzeug.erstzulassung);
    System.out.println("Fahrzeug Leistung: " + meinFahrzeug.leistung);
    class Auto
    public String name;
    public int erstzulassung;
    public int leistung;
    the sdk says:
    klassenobjekttest.java:6: non-static variable this cannot be referenced from a s
    tatic context
    meinFahrzeug = new Auto();
    ^
    1 error
    what's wrong?

    However if i use:
    public class klassenobjekttest
    Auto meinFahrzeug;//brought this line out of main
    public static void main(String[] args)
    meinFahrzeug = new Auto();
    meinFahrzeug.name = "Porsche";
    meinFahrzeug.erstzulassung = 1933; // woher soll ich das wissen?
    meinFahrzeug.leistung = 300;
    System.out.println("Fahrzeug name: " + meinFahrzeug.name);
    System.out.println("Fahrzeug Erstzulassung: " + meinFahrzeug.erstzulassung);
    System.out.println("Fahrzeug Leistung: " + meinFahrzeug.leistung);
    class Auto
    public String name;
    public int erstzulassung;
    public int leistung;
    It does not work.
    could somebody tell me why.
    Appreciate the help
    Thanks,
    Preetham.

  • Non Static Variable addressed to Static Variable

    Hi,
    I am new to java, I am getting (Non Static Variable sb,serverAddress addressed to Static Variable)
    Here is the code. Thanks for reading, any help or explanation would be appreciated-
    * To change this template, choose Tools | Templates
    * and open the template in the editor.
    package webcheck;
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.io.OutputStreamWriter;
    import java.net.HttpURLConnection;
    import java.net.MalformedURLException;
    import java.net.ProtocolException;
    import java.net.URL;
    * @author
    public class checkhttp {
          private URL serverAddress = null;
          private StringBuilder sb = null;
          public checkhttp(java.net.URL serverAddress,java.lang.StringBuilder StringBuilder)
              this.serverAddress=serverAddress;
              this.sb=sb;
      public static void main(String[] args) {
          HttpURLConnection connection = null;
          OutputStreamWriter wr = null;
          BufferedReader rd  = null;
          String line = null;
          int x;
          //checkhttp check= new checkhttp();
          try {
              serverAddress = new URL("http://www.yahoo.com");
              //set up out communications stuff
              connection = null;
              //Set up the initial connection
              connection = (HttpURLConnection)serverAddress.openConnection();
              connection.setRequestMethod("GET");
              connection.setDoOutput(true);
              connection.setReadTimeout(10000);
              connection.connect();
              //get the output stream writer and write the output to the server
              //wr = new OutputStreamWriter(connection.getOutputStream());
              //wr.write("");
              //wr.flush();
              //read the result from the server
              rd  = new BufferedReader(new InputStreamReader(connection.getInputStream()));
              sb = new StringBuilder();
              while ((line = rd.readLine()) != null)
                  sb.append(line + '\n');
              System.out.println(sb.toString());
              System.out.println("Server is up");
          } catch (MalformedURLException e) {
              e.printStackTrace();
          } catch (ProtocolException e) {
              e.printStackTrace();
          } catch (IOException e) {
              e.printStackTrace();
          finally
              //close the connection, set all objects to null
              connection.disconnect();
              //rd = null;
              //sb = null;
              //wr = null;
              connection = null;
    }

    Someone please correct me if I'm wrong, but since main is static, any fields it access must also be static.
    The static keyword declares that something is accessable no matter the class state, thus you can call main() and run your program without having something make an instance of the object that your progam defines. For example:
    class Foo {
          static public String strText = "Hello World";
    //Later in some method, this is valid.
    String MyString = Foo.strText;
    //However, if strText was not static you need to
    Foo fooExample = new Foo();
    String myString = fooExample.strText;Static should not override private, so static private fields/members are not accessable. To be accessable you still need to be public.
    Edited by: porpoisepower on Jan 21, 2010 2:18 PM

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