Compiler thinks getDeclaredFields method is in a static context

Hi folks,
I have the following lines of code at the beginning of a non-static method ;
public void streamOutput(Object objectToStream, boolean autoFlush)
Class objectClass = objectToStream.getClass();
Field[] fieldArray = Class.getDeclaredFields();
When using javac to compile this code I get the following error ;
Can't make static reference to method java.la
ng.reflect.Field getDeclaredFields()[] in class java.lang.Class.
Field[] fieldArray = Class.getDeclaredFields();
^
The thing is that I can't see how javac thinks that the method is being called within a static context. The method is non-static, the containing class in non-static, and I even have a reference to 'this' later on inside the method which the compiler accepts ( which it surely wouldn't if I was working within a static context ).
Any ideas what is wrong ?

The line "Class.getDeclaredFields();" is written as if the method getDeclaredFields() is a static method. It isn't. You have to use an instance of some class. Maybe what you need is objectClass.getClass().getDeclaredFields();

Similar Messages

Non static method cannot be referenced from a non static context

Dear all
I am getting the above error message in my program.
public void testing(Vector XY){
RecStore.checkUnits(XY);
}method checkUnits is non static and cannont be called from a non static context. I don't see the word static anywhere...
I have done a wider search throughout the main class and I'm haven't got any static their either.
Any ideas?
Thanks
Dan

Yup
I had pared down my code, infact it is being called from within a large if statement.Irrelevant.
But the same thing still holds that there is no static keyword used.Read my previous post. Calling checkUnits using the class name:
RecStore.checkUnits(XY);implies a static context--in order for that call to work, checkUnits must be static. That's what your error message is saying--you are trying to call the non-static method "checkUnits" from the static context of using the class name "RecStore."

Question about static context when using classes

hey there.
i'm pretty new to java an here's my problem:
public class kreise {
     public static void main (String[] args) {
         //creating the circles
         create a = new create(1,4,3);
         create b = new create(7,2,5);
         System.out.println(a);
         System.out.println(b);
         //diameters...unimportant right now
         getDiameter a_ = new getDiameter(a.radius);
         getDiameter b_ = new getDiameter(b.radius);
         System.out.println(a_);
         System.out.println(b_);
         //moving the circles
         double x = 2;
         double y = 9;
         double z = 3;
         a = create.move();
         System.out.println(a);
}creating a circle makes use of the class create which looks like this:
public class create {
    public double k1;
    public double k2;
    public double radius;
    public create(double x,double y,double r) {
        k1 = x;
        k2 = y;
        radius = r;
    public create move() {
        k1 = 1;
        k2 = 1;
        radius = 3;
        return new create (k1,k2,radius);
    public String toString() {
    return "Koordinaten: "+k1+" / "+k2+". Radius: "+radius;
}now that's all totally fine, but when i try to usw create.move to change the circles coordinates the compiler says that the non-static method move() can't be referenced from a static context. so far i've seen that my main() funktion MUST be static. when declaring the doubles k1, k2, and radius in create() static it works, but then of course when having created the second circle it overwrites the first one.
i pretty much have the feeling this is very much a standard beginner problem, but searching for the topic never really brought up my problem exactly. thanks in advance!

You can't access a non-static method from within a static context. So, you have to call move() from outside of the main method. main has to be static because, in short, at least one method has to be static because there haven't been any objects initialized when the program is started. There are more fundamental problems than with just the static context issue.
I'm confused by your code though. You call create.move(), but this would only be possible if move() was static, and from what I see, it's not. Now that's just one part of it. My second issue is that the logic behind the move() method is very messy. You shouldn't return a newly instantiated object, instead it should just change the fields of the current object. Also as a general rule, instance fields should be private; you have them as public, and this would be problematic because anything can access it.
Have you heard of getters and setters? That would be what I recommend.
Now, also, when you are "moving" it, you are basically creating a new circle with completely differently properties; in light of this, I've renamed it change(). Here would be my version of your code:
public class CircleTester {
    public static void main (String[] args)
         //Bad way to do it, but here's one way around it:
         new CircleTester().moveCircle();
    private void moveCircle()     //really a bad method, but for now, it'll do
        Circle a = new Circle(1,4,3);
        Circle b = new Circle(7,2,5);
        System.out.println(a);
        System.out.println(b);
        //diameters. Don't need to have a new getDiameter class
        double a_ = a.getRadius() * 2;     //Instead of doing * 2 each time, you could have a method that just returns the radius * 2
        double b_ = b.getRadius() * 2;
        System.out.println(a_);
        System.out.println(b_);
        //move the circle
        a.change(2,9,3);
        System.out.println(a);
public class Circle {
    private double k1;
    private double k2;
    private double radius;
    public Circle(double x,double y,double r)
        k1 = x;
        k2 = y;
        radius = r;
    public void change(int x, int y, int r)
        k1 = x;
        k2 = y;
        radius = r;
    public String toString()
         return "Koordinaten: "+k1+" / "+k2+". Radius: "+radius;
    public double getRadius()
         return radius;
}On another note, there is already a ellipse class: http://java.sun.com/j2se/1.5.0/docs/api/java/awt/geom/Ellipse2D.html

Does main method have to be static? Is there a way to go around it?

I am trying to write a class that will recursively walk through directory listing of a given ftp adress and store it in a text file in this format:
<path> , DIR // if directory
<path> , file // if file
Since I am not yet experienced to do my own socket programming(tried and did not work out) I used Secure iNet Factory's library. And since I will be running multiple instances of this class I concluded that my fields and methods should not be static. Here is the class I wrote:
import com.jscape.inet.ftp.Ftp;
import com.jscape.inet.ftp.FtpException;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.net.URL;
import java.util.Enumeration;
import java.util.logging.Level;
import java.util.logging.Logger;
public class test {
     private String path = "/";
     private String name;
     private String adres;
     // create new Ftp instance and connect.
     public test(String Name, String Adres) throws IOException {
          name = Name;
          adres = Adres;
          System.out.println("Test class: " + name);
          try {
               Ftp ftp = new Ftp(adres,"anonymous","anonymous");
               ftp.connect();
               Enumeration e = ftp.getDirListing();
               iterate(path, ftp);
               ftp.disconnect();
          catch (FtpException ex) {
               Logger.getLogger(test.class.getName()).log(Level.SEVERE, null, ex);
     void iterate(String aStartingDir, Ftp ftp) throws FtpException, IOException {
          //Set the path.
          path = path + aStartingDir + "/";
          // Change directory.
          ftp.setDir(aStartingDir);
          // Iterate through directory list.
          Enumeration e = ftp.getDirListing();
          while(e.hasMoreElements()){
               Object f = e.nextElement();
               // Recursive call if item is directory.
               if(f.toString().startsWith("drwxrwxrwx") &&
                    // Ignore "." and ".."
                    !f.toString().substring(55).trim().equalsIgnoreCase(".") &&
                    !f.toString().substring(55).trim().equalsIgnoreCase("..")) {
                    // Write to index file.
                    URL dirUrl = FtpCheck.class.getResource("./index/"); // get the directory.
                    URL fileUrl = new URL(dirUrl, name + ".txt"); // construct the file path.
                    String filePath = fileUrl.getPath().replaceAll("%20", " "); // fix spaces.
                    BufferedWriter file = new BufferedWriter(new FileWriter(filePath,true));
                    file.write((path + f.toString().substring(55).trim()).substring(3)
                         + ",DIR\n");
                    file.close();
                    iterate(f.toString().substring(55).trim(),ftp);
               // Skip entries "." and ".."
               else if (f.toString().substring(55).trim().equalsIgnoreCase(".") ||
                         f.toString().substring(55).trim().equalsIgnoreCase("..")) {
                         continue;
               // Add files to the index.
               else {
                    URL dirUrl = FtpCheck.class.getResource("./index/"); // get the directory.
                    URL fileUrl = new URL(dirUrl, "index.txt"); // construct the file path.
                    String filePath = fileUrl.getPath().replaceAll("%20", " "); // fix spaces.
                    BufferedWriter file = new BufferedWriter(new FileWriter(filePath,true));
                    file.write((path + f.toString().substring(55).trim()).substring(3)
                         + ",file\n");
                    file.close();
          // End of listing reached, go one directory up.
          ftp.setDirUp();
          // And remove the last directory name from path.
          path = path.substring(0,path.lastIndexOf("/"));
          path = path.substring(0,path.lastIndexOf("/")) + "/";
}which compiles fine.
Here is the class that invokes it:
import java.io.FileNotFoundException;
import java.io.IOException;
import java.net.MalformedURLException;
import java.util.logging.Level;
import java.util.logging.Logger;
* @author Sentinel
public class NewClass {
     public NewClass() {
     public static void main(String args[]) throws MalformedURLException, FileNotFoundException, IOException {
          index t = new index("El Naga","elnaga.sytes.net");
          t.start();
          index t1 = new index("Afacan","afacan.myftp.org");
          t1.start();
     public class index extends Thread {
          String name;
          String adres;
        public index(String Name,String Adres) {
            name = Name;
            adres = Adres;
        @Override
        public void run() {
            try {
                test checker = new test(name,adres);
            catch (IOException ex) {
                 Logger.getLogger(NewClass.class.getName()).log(Level.SEVERE, null, ex);
}when I hit run build fails:
init:
deps-jar:
Compiling 1 source file to C:\Documents and Settings\Sentinel\My Documents\NetBeansProjects\ftpCheck\build\classes
C:\Documents and Settings\Sentinel\My Documents\NetBeansProjects\ftpCheck\src\NewClass.java:19: non-static variable this cannot be referenced from a static context
                index t = new index("El Naga","elnaga.sytes.net");
                          ^
C:\Documents and Settings\Sentinel\My Documents\NetBeansProjects\ftpCheck\src\NewClass.java:20: non-static variable this cannot be referenced from a static context
                index t1 = new index("Afacan","afacan.myftp.org");
                           ^
2 errors
BUILD FAILED (total time: 0 seconds)I (now)know that main method has to be static. I'm stuck and in need of help to overcome this obstacle. Is there a way to do this?

a stab in the dark, but what if you make index a non-internal class. make it a stand-alone class in it's own file. Either that or make it a static inner class (almost the same thing).
Your problem is that an inner class needs an instance of the outer class to start on, and you're not doing this. Another solution would be to do this kludge:
index t = new NewClass().new index("El Naga","elnaga.sytes.net"); // I think this is how to call itBut again better is to make index a stand-alone class.
Edited by: Encephalopathic on Oct 28, 2008 8:06 AM

Non-static method cannot be referenced from a static context....again sry

Hey, I know you guys have probably seen a lot of these, but its for an assignment and I need some help. The error I'm getting is: non-static method printHistory() cannot be referenced from a static context. Here are the classes effected
public class BankAccount {
private static int nextAccountNumber = 1000;
//used to generate account numbers
private String owner; //name of person who owns the account
private int accountNumber; //a valid and unique account number;
private double balance; //amount of money in the account
private TransactionHistory transactions; //collection of past transactions
private Transaction transaction;
//constructor
public BankAccount(String anOwnerName){
owner = anOwnerName;
accountNumber = nextAccountNumber++;
balance = 0.0;
transactions = new TransactionHistory();
//public String getOwner() {
public void deposit(double anAmount ){
     balance=balance+anAmount;
     transaction=new Transaction(TransactionType.DEPOSIT,accountNumber,anAmount,balance);
     transactions.add(transaction);
//public void withdraw(double anAmount){
//public String toString() {
***public void printHistory(){
     TransactionHistory.printHistory();
AND
public class TransactionHistory {
final static int CAPACITY = 6; //maximum number of transactions that can be remembered
//intentionally set low to make testing easier
private Transaction[] transactions = new Transaction[CAPACITY];
//array to store transaction objects
private int size = 0;
//the number of actual Transaction objects in the collection
public void add(Transaction aTransaction){
     if (size>5){
     transactions[0]=transactions[1];
     transactions[1]=transactions[2];
     transactions[2]=transactions[3];
     transactions[3]=transactions[4];
     transactions[4]=transactions[5];
     transactions[5]=aTransaction;
     transactions[size]=aTransaction;
     size=size++;
public int size() {
     return size;
***public void printHistory() {
     for(int i=0;i<6;i++){
          System.out.println(transactions);
//public void printHistory(int n){
The project still isn't finished, so thats why some code is commented out. The line with *** infront on it are the methods directly effected, I think. Any help would be great.

In Java, static means "something pertaining to an object class". Often, the term class is substituted for static, as in "class method" or "class variable." Non-static, on the other hand, means "something pertaining to an actual instance of an object. Similarly, the term +instance+ is often substituted for +non-static+, as in "instance method" or "instance variable."
The error comes about because static members (methods, variables, classes, etc.) don't require an instance of the object to be accessed; they belong to the class. But a non-static member belongs to an instance -- an individual object. There's no way in a static context to know which instance's variable to use or method to call. Indeed, there may not be any instances at all! Thus, the compiler happily tells you that you can't access an instance member (non-static) from a class context (static).
~

Non-static method close() cannot be referenced from a static context

Friends,
I am having a little help with some static and not static issues.
I created a JMenuBar, it's in the file: SlideViewMenu.java
One of the operations is File->Close and another is File->Exit.
The listener is in the SlideViewMenu.java file. The listener needs to reference two non-static methods within SlideView.java.
Here's some of the code:
SlideViewMenu.java
public class SlideViewMenu {
    public JMenuBar createMenuBar() {
    final Action openAction = new OpenAction();
    Action aboutAction = new AboutAction();
    ActionListener menuListener = new MenuActionListener();
    JMenuBar menuBar = new JMenuBar();
     // All the menu stuff works fine and is taken care of here.
   // Listener for Menu
   class MenuActionListener implements ActionListener {
     public void actionPerformed (ActionEvent actionEvent) {
          String selection = (String)actionEvent.getActionCommand();
         if (selection.equals("Close"))
          SlideViewFrame.close();
         else SlideViewFrame.exit();
}SlideView.java
// Driver class
public class SlideView {
     public static void main(String[] args) {
          ExitableJFrame f = new SlideViewFrame("SlideView");
                // Stuff here, works fine.
// Frame class
class SlideViewFrame extends ExitableJFrame {
        // some things here, work fine.
     private SlideViewMenu menuBar = new SlideViewMenu();
     public SlideViewFrame(String title) {
     // Set title, layout, and background color
     super(title);
     setJMenuBar(menuBar.createMenuBar());
        // Stuff here works fine.
     // Handles doing stuff once the file has been selected
     public void setFileName(File fullFileName, String simpleName) {
        // Stuff here works fine.
     // File->Close. clean up everything.
     public void close() {
          setTitle("SlideView");
          textArea.setText("");
          scrollBar.setVisible(false);
          textArea.setVisible(false);
          statsPanel.setVisible(false);
     // File->Exit.
     public void exit() {
          System.exit(0);
}The error I'm getting is:
SlideViewMenu.java:50: non-static method close() cannot be referenced from a static context
I don't get it?
Thanks for all help.

Making close() and exit() static would not solve the problem because close() requires access to nonstatic member variables/functions.
Fortunately, that is not necessary. The real reason you are having a problem is that you don't have any way in your listener to access the main frame window, which is what the listener trying to control. You made a stab at gaining access by prefixing the function with the class name, but, as the compiler has informed you, that is only valid for static methods. If you think about it, you should see the sense in that, because, what if you had a number of frames and you executed className.close()? Which one would you close? All of them?
Fortunately, there is an easy way out that ties the listener to the frame.
SlideViewMenu.java:public class SlideViewMenu
// Here's where we keep the link to the parent.
private SlideViewFrame parentFrame;
// Here's where we link to the parent.
public JMenuBar createMenuBar(SlideViewFrame linkParentFrame)
    parentFrame = linkParentFrame;
    final Action openAction = new OpenAction();
    Action aboutAction = new AboutAction();
    ActionListener menuListener = new MenuActionListener();
    JMenuBar menuBar = new JMenuBar();
    // All the menu stuff works fine and is taken care of here.
// Listener for Menu --- It is assumed that this is a non-static nested
// class in SlideViewMenu. All SlideViewMenu variables are accessible from
// here. If this is not the case, simply add a similar member variable
// to this class, initialize it with a constructor parameter, and
// pass the SlideViewMenu parentFrame when the listener is
// constructed.
class MenuActionListener implements ActionListener
    public void actionPerformed (ActionEvent actionEvent)
      String selection = (String)actionEvent.getActionCommand();
      // Use parentFrame instead of class name.
      if (selection.equals("Close"))
          parentFrame.close();
        else
          parentFrame.exit();
}SlideView.java// Driver class
public class SlideView
public static void main(String[] args)
    ExitableJFrame f = new SlideViewFrame("SlideView");
    // Stuff here, works fine.
// Frame class
class SlideViewFrame extends ExitableJFrame
// some things here, work fine.
private SlideViewMenu menuBar = new SlideViewMenu();
public SlideViewFrame(String title)
    // Set title, layout, and background color
    super(title);
    //Here's where we set up the link.
    setJMenuBar(menuBar.createMenuBar(this));
// Stuff here works fine.
// Handles doing stuff once the file has been selected
public void setFileName(File fullFileName, String simpleName)
    // Stuff here works fine.
// File->Close. clean up everything.
public void close()
    setTitle("SlideView");
    textArea.setText("");
    scrollBar.setVisible(false);
    textArea.setVisible(false);
    statsPanel.setVisible(false);
// File->Exit.
public void exit()
    System.exit(0);
}

Non-static method rff() cannot be referenced from a static context

I get the above error when compiling my program, can anybody see what the problem is and how to fix it? its at the readstr = rff(); part after the if (i==2)
import java.io.*;
import java.util.Vector;
public class PropertyRental
    public static Vector v = new Vector();
    public static String menu;
    public static String pc, hn, mr, ua, readstr;
    public static int i, ln;
    public static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    public String rff()
        String line="";
        String data="";
        try
        BufferedReader br = new BufferedReader(new FileReader("properties.txt"));
        line = br.readLine();
            do// EOF condition
            System.out.println(line);
            data = data + " \n" + line;
            //line = br.readLine();
        while( (line=br.readLine()) != null);
        catch(IOException ioe)
        return data;
    public static void main()
        try
            do
            System.out.println("Welcome to your local Property Rental Company");
            System.out.println("You now have the following options");
            System.out.println("");
            System.out.println("1. Add a Property");
            System.out.println("2. Remove a Property");
            System.out.println("3. Display all Properties");
            System.out.println("4. Exit the Program");
            System.out.println("");
            i = Double.valueOf(br.readLine()).intValue();
            System.out.println("");
            if(i == 1)
                //BufferedWriter appends to properties.txt
                //Our user input buffer
                BufferedReader user = new BufferedReader(new InputStreamReader(System.in));
                System.out.println("--- Add a Property ---");
                    //User enters address
                    System.out.println("\nEnter postcode (Must be less than 16 characters)");
                    pc = user.readLine();
                    //If the user has entered 'q' to quit, leave this loop
                    System.out.println("Enter house number");
                    hn = user.readLine();
                    System.out.println("Enter monthly rent");
                    mr = user.readLine();
                    //Write our details to file
                    v.addElement(new PropertyToLet(pc, hn, mr));
                    PrintWriter outFile;
                    try
                        outFile = new PrintWriter(new FileWriter("properties.txt" ,true));
                        PropertyToLet obj = (PropertyToLet) (v.lastElement());
                        outFile.println(obj.getpc() + "," + obj.gethn() + "," + obj.getmr());
                        outFile.close();
                    catch(IOException IOE)
                        System.err.println(IOE + "Has occured");
            if(i == 2)
               try
                   readstr = rff();
                   String[] splitArray = null;
                   splitArray = readstr.split(",");
                   for(int i=0;i<splitArray.length;i++)
                       if (v.size()<splitArray.length)
                            v.addElement(new PropertyToLet(splitArray[0], splitArray[1], splitArray[2])) ;
                   System.out.println("\nEnter the line number of the property you wish to remove");
                   int ln = Double.valueOf(br.readLine()).intValue();
                   v.removeElementAt(ln-1);
                   PrintWriter outFile = new PrintWriter(new FileWriter("properties.txt"));
                   for (int i=0; i<v.size(); i++)
                        PropertyToLet obj = (PropertyToLet) (v.lastElement());
                        outFile.println(obj.getpc() + "," + obj.gethn() + "," + obj.getmr());
                   outFile.close();
                catch(Exception ex)
                    ex.printStackTrace();
            if(i == 3)
                  String line="";
                  String data="";
                  try
                      BufferedReader br = new BufferedReader(new FileReader("properties.txt"));
                      line = br.readLine();
                      int counter=0;
                      do// EOF condition
                          counter++;
                          System.out.println(counter + ": " + line);
                          data = data + " \n" + line;
                          //line = br.readLine();
                      while( (line=br.readLine()) != null);
                      catch(IOException ioe)
            if(i == 4)
                //A simple instruction that tells the user how to exit the program
                System.out.println("Press the 'x' button in the corner of the window to quit");
            System.out.println("Do you want to exit [y/n]");
            ua = br.readLine();
            }while(ua.equals ("n"));
        catch(IOException ioe)
}Edited by: Atomika3000 on Apr 23, 2009 4:09 AM

You must add modifier method to be static because you access the method from the main method which is a static method
public static String rff(){
// code
}     I hope it helps you, good luck.

Non-static method getRealPath cannot be referenced from a static context

Hi, I'm fairly new to java and servlets, I get the following error referencing the line denoted in the code snippet with a ">>" I don't understand why I am getting this error message?
Message: non-static method getRealPath(java.lang.String) cannot be referenced from a static context
public class events extends HttpServlet implements SingleThreadModel {
private static final String CONTENT_TYPE = "text/html";
//Initialize global variables
public Document xmlDocument;
public HttpSession theSession;
public RequestDispatcher pageInit;
public RequestDispatcher pageHeader;
public RequestDispatcher pageFooter;
public String path;
public void setPath(){
path = getServletContext.getRealPath( "/" ); }
public void init() throws ServletException {
}

Ok More Code, I am weary of posting too much? I don't know why come to think of it?
package altitude;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import org.jdom.*;
import altitude.sysVar;
public class events extends HttpServlet implements SingleThreadModel {
private static final String CONTENT_TYPE = "text/html";
//Initialize global variables
public Document xmlDocument;
public HttpSession theSession;
public RequestDispatcher pageInit;
public RequestDispatcher pageHeader;
public RequestDispatcher pageFooter;
public String path;
public void getRealPath(){
    path = ServletContext.getRealPath( "/" );
public void init() throws ServletException {
//Process the HTTP Get request
public void doGet( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException {
    //Initialise some Global Variables
    theSession = request.getSession( true );
    doPage( request, response );
//Process the HTTP Post request
public void doPost( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException {
    //Initialise some Global Variables
    theSession = request.getSession( true );
    doPage( request, response );
public void doPage( HttpServletRequest request, HttpServletResponse response ) throws ServletException, IOException {
    //Initialise the variables and get the parameters from the query string.
    String eventID = request.getParameter( "eventID" );
    String dateFrom = request.getParameter( "dateFrom" );
    String dateTo = request.getParameter( "dateTo" );
    theSession.setAttribute( "Page Title", sysVar.servletTitle_events);
    Calendar theCalendar = Calendar.getInstance();
    RequestDispatcher pageInit = request.getRequestDispatcher( sysVar.servlet_initSession );
    pageInit.include( request, response );
    RequestDispatcher pageHeader = request.getRequestDispatcher( theSession.getAttribute( "Skin Directory" ) + sysVar.page_header );
    RequestDispatcher pageBody = request.getRequestDispatcher( sysVar.servletJsp_events );
    RequestDispatcher pageFooter = request.getRequestDispatcher( theSession.getAttribute( "Skin Directory" ) + sysVar.page_footer );
    //Initailize the site for this visitor this sets up the skin, and any customisations that may exist.
    //load variables, objects in to the session
    theSession.setAttribute( "Xml Document Object", path + sysVar.data_events );
    pageHeader.include( request, response );
    pageBody.include( request, response );
    pageFooter.include( request, response );
    //remove the variables and the objects from the session
    theSession.setAttribute( "Xml Document Object", "" );
//Clean up resources
public void destroy() {
}

How the compiler chooses which method to invoke?

public class A {
        public void foo(Object o) {
            System.out.println("A.foo with an object");
public class B extends A {
        public void foo(Object o) {
            System.out.println("B.foo with an object");
        public void foo(String s) {
            System.out.println("B.foo with a string");
public class C {
    public static void main(String[] args) {
        String s = "hello";
        A a = new B();
        a.foo(s);
}why the output is "B.foo with an object" and not "B.foo with a String".
or more generally: how the compiler choses the method to invoke?

or more generally: how the compiler choses the method
to invoke?Variable a is declared as a reference to an A. The compiler only knows this. It doesn't know that the object it happens to be pointing at is a B. So it only looks at A's methods.
A has only foo(Object), so it will call the method with the signature foo(Object).
Which signature to use is determined at compile time, and is determined by the type of the reference.
Now, as for whether A's foo or B's foo, that's where Java's polymorphism comes in. In this case, the VM looks at the object, not the reference, and calls the "deepest" (furthest from Object) class' method that matches that signature.
Which class' implementation of that signature to call is determined at runtime, and is determined by the object, not the reference.

Non-static method cannot be referenced from a static context

Hey
Im not the best java programmer, im trying to teach myself, im writing a program with the code below.
iv run into a problem, i want to call the readFile method but i cant call a non static method from a static context can anyone help?
import java.io.*;
import java.util.*;
public class Trent
String processArray[][]=new String[20][2];
public static void main(String args[])
String fName;
System.out.print("Enter File Name:");
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
fName="0";
while (fName=="0"){
try {
fName = br.readLine();
System.out.println(fName);
readFile(fName);
catch (IOException ioe)
System.out.println("IO error trying to read File Name");
System.exit(1);
public void readFile(String fiName) throws IOException {
File inputFile = new File(fiName); //open file for reading
FileReader in = new FileReader(inputFile); //
BufferedReader br = new BufferedReader(
new FileReader(inputFile));
String first=br.readLine();
System.out.println(first);
StringTokenizer st = new StringTokenizer(first);
while (st.hasMoreTokens()) {
String dat1=st.nextToken();
int y=0;
for (int x=0;x<=3;){
processArray[y][x] = dat1;
System.out.println(y + x + "==" + processArray[y][x]);
x++;
}

Hi am getting the same error in my jsp page:
Hi,
my adduser.jsp page consist of form with field username,groupid like.
I am forwarding this page to insertuser.jsp. my aim is that when I submit adduser.jsp page then the field filled in form should insert into the usertable.The insertuser.jsp is like:
<% String USERID=request.getParameter("id");
String NAME=request.getParameter("name");
String GROUPID=request.getParameter("group");
try {
Class.forName("com.mysql.jdbc.Driver");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/mynewdatabase","root", "root123");
PreparedStatement st;
st = con.prepareStatement("Insert into user values (1,2,4)");
st.setString(1,USERID);
st.setString(2,GROUPID);
st.setString(4,NAME);
// PreparedStatement.executeUpdate();//
}catch(Exception ex){
System.out.println("Illegal operation");
%>
But showing error at the marked lines lines as:non static method executeupdate can not be referenced from static context.
Really Speaking I am newbie in this java world.
whether you have any other solution for above issue?
waiting Your valuable suggestion.
Thanks and regards
haresh

Non-static method getIDnumber() cannot be referenced from a static context

Student.java
public class Student
     private int IDnumber;
     private int hours;
     private int points;
     public Student()
   IDnumber = 9999;
   points = 12;
   hours = 3;
     public void setIDnumber(int number)
     IDnumber = number;
   public int getIDnumber()
     return IDnumber;
   public void setHours(int number)
   hours = number;
   public int getHours()
   return hours;
   public void setPoints(int number)
   points = number;
   public int getPoints()
   return points;
     public void showIDnumber()
   System.out.println("ID Number is " + IDnumber);
   public void showHours()
   System.out.println("Credit Hours are " + hours);
   public void showPoints()
   System.out.println("Points Earned are " + points);
   public double getGradePoint()
   return (double) (points / hours);
ShowStudent.java
public class ShowStudent
     public static void main(String[] args)
          Student learner = new Student();
          int IDnumber;
          int points;
          int hours;
          IDnumber = Student.getIDnumber();
          points = Student.getPoints();
          hours = Student.getHours();
          System.out.println("ID number is " + IDnumber);
          System.out.println("Hours are " + hours);
          System.out.println("Points are " + points);
Here I get the following. How do I fix this? Thanks.
ShowStudent.java:9: non-static method getIDnumber() cannot be referenced from a
static context
IDnumber = Student.getIDnumber();
^
ShowStudent.java:10: non-static method getPoints() cannot be referenced from a
static context
points = Student.getPoints();
^
ShowStudent.java:11: non-static method getHours() cannot be referenced from a s
tatic context
hours = Student.getHours();
^
3 errors

You have to get the ID number of a particular instance i.e. IDnumber = learner.getIDnumber();

Non-static method getPerimeter() cannot be referenced from a static context

I am getting this error message. I assume it is because getArea( ) and getPerimeter( ) are nonstatic and main is static? Can somebody help me? Thanks in advance!
Error messages:
non-static method getArea() cannot be referenced from a static context
          System.out.println("\nArea: " + onePlace.format(getArea()));
non-static method getPerimeter() cannot be referenced from a static context
          System.out.println("Perimeter: " + onePlace.format(getPerimeter()));
import java.util.Scanner;
import java.text.DecimalFormat;
public class Rectangle
     public double length;
     public double width;
     public Rectangle()
          length = 0;
          width = 0;
     public double getLength()
          return length;
     public double getWidth()
          return width;
     public void setLength(double length)
          this.length = length;
     public void setWidth(double width)
          this.width = width;
     public double getArea()
          return (length * width);
/*     public double area(Rectangle R)
          double area = length * width;
          return area;
     public double getPerimeter()
          return ((length * 2) + (width * 2));
/*     public double perimeter(Rectangle R)
          double perimeter = (length * 2) + (width * 2);
          return perimeter;
/*     public String toString()
          double area = 0;
          double perimeter = 0;
          return "Area: " + area + "\tPerimeter: " + perimeter;
     public static void main(String [] args)
          DecimalFormat onePlace = new DecimalFormat("#0.0");
          Rectangle R = new Rectangle();
          Rectangle L = new Rectangle();
          Rectangle W = new Rectangle();
          Scanner input = new Scanner(System.in);
          System.out.println("Enter length of rectangle: ");
          L.setLength(input.nextDouble());
          System.out.println("\nEnter width of rectangle: ");
          W.setWidth(input.nextDouble());
          System.out.println("\nArea: " + onePlace.format(getArea()));
          System.out.println("Perimeter: " + onePlace.format(getPerimeter()));
//          System.out.println(R.toString());
}

For some reason, something isn't being read.
This is what I get:
Enter length of rectangle:
2
Enter width of rectangle:
4
Area: 0.0
Perimeter: 0.0
Press any key to continue . . .
Is it what I have to scan the input (L.setLength...)?
     public static void main(String [] args)
          DecimalFormat onePlace = new DecimalFormat("#0.0");
          Rectangle R = new Rectangle();
          Rectangle L = new Rectangle();
          Rectangle W = new Rectangle();
          Scanner input = new Scanner(System.in);
          System.out.println("Enter length of rectangle: ");
          L.setLength(input.nextDouble());
          System.out.println("\nEnter width of rectangle: ");
          W.setWidth(input.nextDouble());
          System.out.println("\nArea: " + onePlace.format(R.getArea()));
          System.out.println("Perimeter: " + onePlace.format(R.getPerimeter()));
//          System.out.println(R.toString());
}

Using java.lang.reflect.Method.invoke on a static method?

This is probably a FAQ, but I am finding it impossible to construct a search which answers this question for me.
How do I call java.lang.reflect.Method.invoke on a static (e.g. class) method? Is it even possible?
Thanks,
dwh

Is this of any help?
http://www.esus.com/javaindex/j2se/jdk1.2/javalang/reflection/reflection.html
Cheers,
Joris

Painting jpeg in java application: non-static method ... static context

Hi!
I simply want to show a jpeg within a java application. Showing the jpeg in an applet is no problem (see code below). But I have difficulties to translate this code to a java application. No matter what I try to load the jpeg, I end up with the following error:
non-static method createImage() cannot be referenced from a static context
How can I surround it? Thanx in advance for your help!
Working applet
import java.applet.*;
import java.awt.*;
public class shJpAp extends javax.swing.JApplet {
Image pic;
/** Creates a new instance of shJpAp */
public shJpAp() {
public void init() {
pic=getImage(getCodeBase(), "lemmer.jpg");
prepareImage(pic,this);
public void paint (Graphics g) {
g.drawImage(pic,0,0,this);
Application
import java.awt.*;
public class shJp extends javax.swing.JFrame {
Image pic;
/** Creates new form shJp */
public shJp() {
initComponents();
//pic = java.awt.Toolkit.getImage("lemmer.jpg");
---> pic = java.awt.Toolkit.createImage("lemmer.jpg");
---> prepareImage(pic, this);
/** This method is called from within the constructor to
* initialize the form.
* WARNING: Do NOT modify this code. The content of this method is
* always regenerated by the Form Editor.
private void initComponents() {
addWindowListener(new java.awt.event.WindowAdapter() {
public void windowClosing(java.awt.event.WindowEvent evt) {
exitForm(evt);
pack();
/** Exit the Application */
private void exitForm(java.awt.event.WindowEvent evt) {
System.exit(0);
* @param args the command line arguments
public static void main(String args[]) {
new shJp().show();
// Variables declaration - do not modify
// End of variables declaration
public void paint( Graphics g) {
g.drawImage(pic, 0,0,this);
}

Hi,
just want to add a solution I found in some textbook (see code below). I hate finding every possible question in the internet, but seldom fitting answers.....
But again, one little thing pushed me close to my first heart attack: The code below works well when executed by foot (...java showPic...). In the NetBeans 3.6 the frame refuses to show the pic!
I am looking for an appropiate forum - but if anyone of you can help, it would be very nice ;-)
import java.awt.*;
import java.awt.event.*;
public class showPic extends Frame {
Image pic;
public showPic() {
addWindowListener( new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
pic = getToolkit().getImage("lemmer.jpg");
setSize(200,100);
setVisible(true);
public void paint(Graphics g) {
if (pic != null) {
g.drawImage(pic,60,20,this);
public static void main( String[] args ) {
new showPic();
}

Non-static variable cant accessed from the static context..your suggestion

Once again stuck in my own thinking, As per my knowledge there is a general error in java.
i.e. 'Non-static variable cant accessed from static context....'
Now the thing is that, When we are declaring any variables(non-static) and trying to access it within the same method, Its working perfectly fine.
i.e.
public class trial{
�� public static void main(String ar[]){ ////static context
�� int counter=0; ///Non static variable
�� for(;counter<10;) {
�� counter++;
�� System.out.println("Value of counter = " + counter) ; ///working fine
�� }
�� }
Now the question is that if we are trying to declare a variable out-side the method (Non-static) , Then we defenately face the error' Non-static varialble can't accessed from the static context', BUT here within the static context we declared the non-static variable and accessed it perfectly.
Please give your valuable suggestions.
Thanks,
Jeff

Once again stuck in my own thinking, As per my
knowledge there is a general error in java.
i.e. 'Non-static variable cant accessed from static
context....'
Now the thing is that, When we are declaring any
variables(non-static) and trying to access it within
the same method, Its working perfectly fine.
i.e.
public class trial{
�� public static void
main(String ar[]){ ////static context
�� int counter=0; ///Non
static variable
�� for(;counter<10;) {
�� counter++;
��
System.out.println("Value
of counter = " + counter) ; ///working fine
�� }
�� }
w the question is that if we are trying to declare a
variable out-side the method (Non-static) , Then we
defenately face the error' Non-static varialble can't
accessed from the static context', BUT here within
the static context we declared the non-static
variable and accessed it perfectly.
Please give your valuable suggestions.
Thanks,
JeffHi,
You are declaring a variable inside a static method,
that means you are opening a static scope... i.e. static block internally...
whatever the variable you declare inside a static block... will be static by default, even if you didn't add static while declaring...
But if you put ... it will be considered as redundant by compiler.
More over, static context does not get "this" pointer...
that's the reason we refer to any non-static variables declared outside of any methods... by creating an object... this gives "this" pointer to static method controller.

Compiler thinks getDeclaredFields method is in a static context

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