Static method decisions

Dear all experts,
I have got some problems understanding when to use static methods or passing the classes through constructor.
I have got a class which needs to be accessed by several classes and also the classes inside the classes etc....
Instead of passing classes around, should I just create a single static class which can be accessed by all the classes without needing to instantiate the class?
I found that, i particularly in doubt when there are classes like "TableParser", "PropertiesReader" etc which some classes deep down in the hierarchy need access to those classes...
Also, making the class static would it decrease the security of the whole program?? Say if i have got an encrytion class which does all the encrypt and decrypt, if i let it be static, isn't it easier to let people accessing the method? the same applies to properties editor etc??
Any help would be really appreciated.
Thx

thx again jverd... (remember the security question? :)
)I remember your id, but I didn't recall which thread(s) I had seen it in.
>
based on the understanding of what you said, do you
mean that, if i am only using a class to store or read
a setting file, it's ok to let it static? (so that all
classes can access it whenever they like without
passing the parser class to classes?)Um, again, you're terminology's a little off, so I'm not sure exactly what you mean, and even the description "store or read a seting file" could have a couple of interpretations.
For example....You read the file once, and the config data it constains is accessible throughout your app and never changes. This might be a candidate for a class that only had static methods, but it would be kind of inflexible. What if later some other part of your app, or some other library that you develop that your app is going to use, wants to get its configuration from a file. In that case, I might want to have a couple instances of that class around. One for the global config that reads one file, and another for the config for that library that might read another file.
I'd probably not even think about it as "reading a settings file." Rather, I'd see that as two parts: providing config settings to the app via a class, and reading a file to populate that class. The settings would exist independent of the fact that you can populate them from a file.
I'd think about how I want to use them and decide whether to instantiate the class or use static methods based on that. Separately, I'd think about how this class or an instance of it is gonna get popuated with data from outside the program.
I might decide to have different instances hold different sets of config data, and therefore use instance (non-static) methods to access the data in each of those instances, but I might register the instances--say by name, or maybe just in a list--and I could use a static method to acess the map or list: Config dbConfig = Config.getConfig("database"); Also, I wouldn't generally make a decsision on whether to use class methods or instance methods based on not having to pass a parameter.
If you're thinking "I'd like to use static because it's easier. Can I get away with it here," then you're viewing objects as a burden to be avoided, which kind of defeats the purpose of using OO techniques in the first place.

Similar Messages

I really need abstract static methods in abstract class

Hello all.. I have a problem,
I seem to really need abstract static methods.. but they are not supported.. but I think the JVM should implement them.. i just need them!
Or can someone else explain me how to do this without abstract static methods:
abstract class A {
abstract static Y getY();
static X getX() {
    // this methods uses getY, for example:
    y=getY();
   return new X(y); // or whatever
class B extends A {
static Y getY() { return YofB; }
class C extends A {
static Y getY() { return YofC; }
// code that actually uses the classes above:
// these are static calls
B.getX();
A.getX();I know this wont compile. How should i do it to implement the same?

Damn i posted this in the wrong thread.. anyways.
Yes offcourse i understand abstract and static
But i have a problem where the only solution is to use them both.
I think it is theoretically possible ot implement a JVM with support for abstract static methods.
In fact it is a design decision to not support abstract static methods.. thats why i am asking this question.. how could you implemented this otherwise?
There is an ugly soluition i think: using Aspect Oriented Programming with for example AspectJ.. but that solution is really ugly. So anyone has an OO solution?

Re: static methods in an interface?

You cannot define a constructor in an interface, (part of the language specification), and static methods belong to the class so how could a derived concrete class possibly implement something that belonged to its ancestor abstract class? Look at the factory pattern & perhaps Singleton for more guidance and seriously consider why you're attempting to do this. In fact, post the reasoning behind this decision and see if there are any useful comments / suggestions on that.

This certainly sounds like a candidate for the Factory pattern, (or one of its specialisations such as Flyweight). Check out the forum here or one of the many sites focused on this area. You'll see that you're trying to solve a common problem in an unnecessarily complex way.

Static methods. Why?

I understand what static means, and that each class has only ONE copy of its static variables and methods.
I an see the benefits of using static variables, but i cant seem to get my head round the benefits of using static methods.
What is the advantage of this, and is there a common situation where they are appropriate? (not main)
Cheers

I don't think static exists to prevent namespace conflicts. I think that the reason for static to exist is just as I described it: When you've got some task that is appropriate to be performed by a specific class, but that doesn't make sense to be associated with a particular instance of that class.
For example, String.valueOf. It's appropriate for the String class to have a method that returns the String representation of anything you feed to it (so it's in the String class) but it doesn't make sense for that method to be associated with a particular instance of String (so it's static). After all, you don't yet have a String to operate on--you're producing the String.
Which raises another interesting point: I wonder what the design decision was that led to
String.valueOf(int)
String.valueOf(long)
String.valueOf(Object)
etc.
instead of
new String(int)
new String(long)
newString(Object)
etc.
I've used both patterns in my own work, but I don't really have any good criteria for picking one over the other.
One thing that comes to mind for the general case is that with the static method, you can return a subclass, which you can't do with a constructor. Conversely, with a constructor, the caller knows exactly which class he'll get, whereas with a static method he doesn't. Of course, these points don't apply to String, as it's final.
I'm new to java, but as far as I can tell, "static"
means "global". The reason for having them in classes
is mainly to prevent name conflicts. For instance,
you could have an Array object, and a List object, and
both could have sort() methods, but they may be very
different types of methods. By forcing sort() to be a
member of a class, instead of a global identifier, you
have Array.sort() and List.sort(), which is much
safer.
It seems that the java designers went to great lengths
to make sure there are no namespace conflicts in the
language. Maybe they even went a bit too far in this
sometimes.

Static Vs Non-static methods

Hello,
I wonder what should I use. I have got a class which does a lot of counting.. I can put the methods inside the class or make a class Math3D with the static methods that will count it.
Which is the better way?

BigDaddyLoveHandles wrote:
deepak_1your.com wrote:
Sorry mate... did not get that.By definition a utility class has all static methods. So as soon as you mention "utility class" you've already made a decision. The real question is "should method X be static or non-static"? My default position is to assume no method should be static, and then wait to be convinced.
Look at utility class java.lang.Math, for example. It has static methods sin(), cos(), sqrt(), etc... An obvious choice for a utility class, right? Then they introduced class StrictMath in 1.3 with exactly the same static method signatures. That's a code smell that one should have written an interface and implemented it in at least two ways, but it's too late for that because the original methods are static.Good post.

Why not to use static methods - with example

Hi Everyone,
I'd like to continue the below thread about "why not to use static methods"
Why not to use static methods
with a concrete example.
In my small application I need to be able to send keystrokes. (java.awt.Robot class is used for this)
I created the following class for these "operations" with static methods:
public class KeyboardInput {
     private static Robot r;
     static {
          try {
               r = new Robot();
          } catch (AWTException e) {
               throw new RuntimeException(e + "Robot couldn't be initialized.");
     public static void wait(int millis){
          r.delay(millis);
     public static void copy() {
          r.keyPress(KeyEvent.VK_CONTROL);
          r.keyPress(KeyEvent.VK_C);
          r.keyRelease(KeyEvent.VK_C);
          r.keyRelease(KeyEvent.VK_CONTROL);
     public static void altTab() {
          r.keyPress(KeyEvent.VK_ALT);
          r.keyPress(KeyEvent.VK_TAB);
          r.keyRelease(KeyEvent.VK_TAB);
          r.keyRelease(KeyEvent.VK_ALT);
               // more methods like paste(), tab(), shiftTab(), rightArrow()
}Do you thinks it is a good solution? How could it be improved? I've seen something about Singleton vs. static methods somewhere. Would it be better to use Singleton?
Thanks for any comments in advance,
lemonboston

maheshguruswamy wrote:
lemonboston wrote:
maheshguruswamy wrote:
I think a singleton might be a better approach for you. Just kill the public constructor and provide a getInstance method to provide lazy initialization.Thanks maheshguruswamy for advising on the steps to create a singleton from this class.
Could you maybe advise also about why do you say that it would be better to use singleton? What's behind it? Thanks!In short, it seems to me that a single instance of your class will be able to coordinate actions across your entire application. So a singleton should be enough.But that doesn't answer why he should prefer a singleton instead over a bunch of static methods. Functionally the two are almost identical. In both cases there's only one "thing" on which to call methods--either a single instance of the class, or the class itself.
To answer the question, the main reason to use a Singleton over a classful of static methods is the same reason the drives a lot of non-static vs. static decisions: Polymorphism.
If you use a Singleton (and and interface), you can do something like this:
KeyboardInput kbi = get_some_instance_of_some_class_that_implements_KeyboardInput_somehow_maybe_from_a_factory();And then whatever is calling KBI's public methods only has to know that it has an implementor of that interface, without caring which concrete class it is, and you can substitute whatever implementation is appropriate in a given context. If you don't need to do that, then the static method approach is probably sufficient.
There are other reasons that may suggest a Singleton--serialization, persistence, use as a JavaBean pop to mind--but they're less common and less compelling in my experience.
And finally, if this thing maintains any state between method calls, although you can handle that with static member variables, it's more in keeping with the OO paradigm to make them non-static fields of an instance of that class.

Compilation error while calling static method from another class

Hi,
I am new to Java Programming. I have written two class files Dummy1 and Dummy2.java in the same package Test.
In Dummy1.java I have declared a static final variable and a static method as you can see it below.
package Test;
import java.io.*;
public class Dummy1
public static final int var1= 10;
public static int varDisp(int var2)
return(var1+var2);
This is program is compiling fine.
I have called the static method varDisp from the class Dummy2 and it is as follows
package Test;
import java.io.*;
public class Dummy2
public int var3=15;
public int test=0;
test+=Dummy1.varDisp(var3);
and when i compile Dummy2.java, there is a compilation error <identifier > expected.
Please help me in this program.

public class Dummy2
public int var3=15;
public int test=0;
test+=Dummy1.varDisp(var3);
}test+=Dummy1.varDisplay(var3);
must be in a method, it cannot just be out somewhere in the class!

Using a non-static vector in a generic class with static methods

I have a little problem with a class (the code is shown underneath). The problem is the Assign method. This method should return a clone (an exact copy) of the set given as an argument. When making a new instance of a GenericSet (with the Initialize method) within the Assign method, the variables of the original set and the clone have both a reference to the same vector, while there exists two instances of GenericSet. My question is how to refer the clone GenericSet's argument to a new vector instead of the existing vector of the original GenericSet. I hope you can help me. Thanks
package genericset;
import java.util.*;
public class GenericSet<E>{
private Vector v;
public GenericSet(Vector vec) {
v = vec;
private <T extends Comparable> Item<T> get(int index) {
return (Item<T>) v.get(index);
public static <T extends Comparable> GenericSet<T> initialize() {
return new GenericSet<T>(new Vector());
public Vector getVector() {
return v;
public static <T extends Comparable> GenericSet<T> insert (GenericSet<T> z, Item<T> i){
GenericSet<T> g = assign(z);
Vector v = g.getVector();
if (!member(g,i))
v.addElement(i);
return g;
public static <T extends Comparable> GenericSet<T> delete(GenericSet<T> z, Item<T> i){
GenericSet<T> g = assign(z);
Vector v = g.getVector();
if (member(g,i))
v.remove(i);
return g;
public static <T extends Comparable> boolean member(GenericSet<T> z, Item<T> i) {
Vector v = z.getVector();
return v.contains(i);
public static <T extends Comparable> boolean equal(GenericSet<T> z1, GenericSet<T> z2) {
Vector v1 = z1.getVector();
Vector v2 = z2.getVector();
if((v1 == null) && (v2 != null))
return false;
return v1.equals(v2);
public static <T extends Comparable> boolean empty(GenericSet<T> z) {
return (cardinality(z) == 0);
public static <T extends Comparable> GenericSet<T> union(GenericSet<T> z1, GenericSet<T> z2) {
GenericSet<T> g = assign(z1);
for(int i=0; i<cardinality(z2); i++) {
Item<T> elem = z2.get(i);
insert(g, elem);
return g;
public static <T extends Comparable> GenericSet<T> intersection(GenericSet<T> z1, GenericSet<T> z2) {
GenericSet<T> g = initialize();
for(int i=0; i<cardinality(z2); i++) {
Item<T> elem = z2.get(i);
if(member(z1, elem))
insert(g, elem);
return g;
public static <T extends Comparable> GenericSet<T> difference(GenericSet<T> z1, GenericSet<T> z2) {
GenericSet<T> g = initialize();
for(int i=0; i<cardinality(z1); i++) {
Item<T> elem = z1.get(i);
if(!member(z2, elem))
insert(g, elem);
for(int i=0; i<cardinality(z2); i++) {
Item<T> elem = z2.get(i);
if(!member(z1, elem))
insert(g, elem);
return g;
public static <T extends Comparable> GenericSet<T> assign(GenericSet<T> z) {
GenericSet<T> g = initialize();
for(int i=0; i<cardinality(z); i++) {
Item<T> elem = z.get(i);
insert(g, elem);
return g;
public static <T extends Comparable> boolean subset(GenericSet<T> z1, GenericSet<T> z2) {
for(int i=0; i<cardinality(z1); i++) {
Item<T> elem = z1.get(i);
if(!member(z2, elem))
return false;
return true;
public static <T extends Comparable> int cardinality(GenericSet<T> z){
Vector v = z.getVector();
return v.size();
}

The issue is not "reference a non-static interface", but simply that you cannot reference a non-static field in a static method - what value of the field ed would the static method use? Seems to me your findEditorData should look something like this:   public static EditorBean findEditorData( String username, EditorBean editorData )
      return editorData.ed.findEditor( username );
   }

Using HttpServletRequest object to share variables between static methods.

Does anyone know of the overhead/performance implications of using the HttpServletRequest object to share variables between a static method and the calling code?
First, let me explain why I am doing it.
I have some pagination code that I would like to share across multiple servlets. So I pulled the pagination code out, and created a static method that these servlets could all use for their pagination.
public class Pagination {
     public static void setPagination (HttpServletRequest request, Config conf, int totalRows) {
          int page = 0;
          if (request.getParameter("page") != null) {
               page = new Integer(request.getParameter("page")).intValue();
          int articlesPerPage = conf.getArticlesPerPage();
          int pageBoundary = conf.getPageBoundary();
            int numOfPages = totalRows / articlesPerPage;
            // Checks if the page variable is empty (not set)
            if (page == 0 || (page > numOfPages && (totalRows % articlesPerPage) == 0 && page < numOfPages + 1)) {
             page = 1; // If it is empty, we're on page 1
          // Ex: (2 * 25) - 25 = 25 <- data starts at 25
         int startRow = page * articlesPerPage - (articlesPerPage);
         int endRow = startRow + (articlesPerPage);
         // Set array of page numbers.
         int minDisplayPage = page - pageBoundary;
         if (minDisplayPage < 1) {
              minDisplayPage = 1;
         int maxDisplayPage = page + pageBoundary;
         if (maxDisplayPage > numOfPages) {
              maxDisplayPage = numOfPages;
         int arraySize = (maxDisplayPage - minDisplayPage) + 1;
         // Check if there is a remainder page (partially filled page).
         if ((totalRows % articlesPerPage) != 0) arraySize++;
         // Set array to correct size.
         int[] pages = new int[arraySize];
         // Fill the array.
         for (int i = 1; i <= pages.length; i++) {
              pages[i - 1] = i;
         // Set pageNext and pagePrev variables.
         if (page != 1) {
              int pagePrev = page - 1;
              request.setAttribute("pagePrev", pagePrev);
         if ((totalRows - (articlesPerPage * page)) > 0) {
             int pageNext = page + 1;
             request.setAttribute("pageNext", pageNext);
         // These will be used by calling code for SQL query.
         request.setAttribute("startRow", startRow);
         request.setAttribute("endRow", endRow);
         // These will be used in JSP page.
         request.setAttribute("totalRows", totalRows);
         request.setAttribute("numOfPages", numOfPages);
         request.setAttribute("page", page);
         request.setAttribute("pages", pages);
}I need two parameters from this method (startrow and endrow) so I can perform my SQL queries. Since this is a multithreaded app, I do not want to use class variables that I will later retrieve through methods.
So my solution was to just set the two parameters in the request and grab them later with the calling code like this:
// Set pagination
Pagination.setPagination(request, conf, tl.getTotalRows());
// Grab variables set into request by static method
int startRow = new Integer(request.getAttribute("startRow").toString());
int endRow = new Integer(request.getAttribute("endRow").toString());
// Use startRow and endRow for SQL query below...Does anyone see any problem with this from a resource/performance standpoint? Any idea on what the overhead is in using the HttpServletRequest object like this to pass variables around?
Thanks for any thoughts.

You could either
- create instance vars in both controllers and set them accordingly to point to the same object (from the App Delegate) OR
- create an instance variable on the App Delegate and access it from within the view controllers
Hope this helps!

Can you set a global EntityResolver (via system property, or static method)

I'm trying to set a customized EntityResolver (telling the xml parser where to look for XML schema files).
Usually, you'd use the standard syntax - somehting like:
SaxParser parser=new SaxParser();
parser.parser.setEntityResolver(myResolver);
However, I was wondering whether you can set a "global" EntityResolver, to be used as default for all parsers ?
Maybe this can be done through some system property, or a static method somewhere in the parsing XML ?
(BTW, I need it because I'm using some third-party API, that encapsulates a SaxParser, but won't let me access it, so I can't configure it directly).
thanks.

I don't think you can.
What is possible is to set content on the folder resource itself; that would be returned instead of the page you mentioned.

How to call a static method from an event handler

Hi,
I'm trying to call a static method of class I designed. But I don't know how to do it. This method will be called from an event handler of a web dynpro for Abap application.
Can somebody help me?
Thx in advance.
Hamza.

To clearly specify the problem.
I have a big part code that I use many times in my applications. So I decided to put it in a static method to reuse the code. but my method calls functions module of HR module. but just after the declaration ( at the first line of the call function) it thows an exception. So I can't call my method.

How to call a static method in a class if I have just the object?

Hello. I have an abstract class A where I have a static method blah(). I have 2 classes that extend class A called B and C. In both classes I override method blah(). I have an array with objects of type B and C.
For every instance object of the array, I'm trying to call the static method in the corresponding class. For objects of type B I want to call blah() method in B class and for objects of type C I want to call blah() method in C class. I know it's possible to call a static method with the name of the object, too, but for some reason (?) it calls blah() method in class A if I try this.
So my question is: how do I code this? I guess I need to cast to the class name and then call the method with the class name, but I couldn't do it. I tried to use getClass() method to get the class name and it works, but I didn't know what to do from here...
So any help would be appreciated. Thank you.

As somebody already said, to get the behavior you
want, make the methods non-static.You all asked me why I need that method to be
static... I'm not surprised to hear this question
because I asked all my friends before posting here,
and all of them asked me this... It's because some
complicated reasons, I doubt it.
the application I'm writing is
quite big...Irrelevant.
Umm... So what you're saying is there is no way to do
this with that method being static? The behavior you describe cannot be obtained with only static methods in Java. You'd have to explicitly determine the class and then explicitly call the correct class' method.

Calling a method from a static method

hello all,
I'm calling a non-static method from a static method (from the main method). To overcome this i can make the method i am calling static but is there another way to get this to work without making the method that is being called static?
all replies welcome, thanks

When you call a non-static method, you are saying you are calling a method on an object. The object is an instance of the class in which the method is defined. It is a non-static method, because the instance holds data in it's instance variables that is needed to perform the method. Therefore to call this kind of method, you need to get (or create an instance of the class. Assuming the two methods are in the same class, you could do
public class Foo
     public static void main(String[] args)
            Foo f = new Foo();
            f.callNonStaticMethod();
}for instance.

Calling a non-static method from another Class

Hello forum experts:
Please excuse me for my poor Java vocabulary. I am a newbie and requesting for help. So please bear with me! I am listing below the program flow to enable the experts understand the problem and guide me towards a solution.
1. ClassA instantiates ClassB to create an object instance, say ObjB1 that
    populates a JTable.
2. User selects a row in the table and then clicks a button on the icon toolbar
    which is part of UIMenu class.
3. This user action is to invoke a method UpdateDatabase() of object ObjB1. Now I want to call this method from UIMenu class.
(a). I could create a new instance ObjB2 of ClassB and call UpdateDatabase(),
                                  == OR ==
(b). I could declare UpdateDatabase() as static and call this method without
     creating a new instance of ClassB.With option (a), I will be looking at two different object instances.The UpdateDatabase() method manipulates
object specific data.
With option (b), if I declare the method as static, the variables used in the method would also have to be static.
The variables, in which case, would not be object specific.
Is there a way or technique in Java that will allow me to reference the UpdateDatabase() method of the existing
object ObjB1 without requiring me to use static variables? In other words, call non-static methods in a static
way?
Any ideas or thoughts will be of tremendous help. Thanks in advance.

Hello Forum:
Danny_From_Tower, Encephalatic: Thank you both for your responses.
Here is what I have done so far. I have a button called "btnAccept" created in the class MyMenu.
and declared as public.
public class MyMenu {
    public JButton btnAccept;
     //Constructor
     public MyMenu()     {
          btnAccept = new JButton("Accept");
}     I instantiate an object for MyMenu class in the main application class MyApp.
public class MyApp {
     private     MyMenu menu;
     //Constructor
     public MyApp(){
          menu = new MyMenu();
     public void openOrder(){
           MyGUI MyIntFrame = new MyGUI(menu.btnAccept);
}I pass this button all the way down to the class detail02. Now I want to set up a listener for this
button in the class detail02. I am not able to do this.
public class MyGUI {
     private JButton acceptButton;
     private detail02 dtl1 = new detail02(acceptButton);
     //Constructor
     public AppGUI(JButton iButton){
     acceptButton = iButton;
public class detail02{
    private JButton acceptButton;
    //Constructor
    public detail02(JButton iButton){
      acceptButton = iButton;
      acceptButton.addActionListener(new acceptListener());
   //method
    private void acceptListener_actionPerformed(ActionEvent e){
       System.out.println("Menu item [" + e.getActionCommand( ) + "] was pressed.");
    class acceptListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
               acceptListener_actionPerformed(e);
} I am not able to get the button Listener to work. I get NullPointerException at this line
          acceptButton.addActionListener(new acceptListener());in the class detail02.
Is this the right way? Or is there a better way of accomplishing my objective?
Please help. Your inputs are precious! Thank you very much for your time!

Calling a static method from another class

public class Command
    public static void sortCommands(String command, String order, List object)
         if(command.equalsIgnoreCase("merge") && order == "a")
              object.setAscending(true);
              Mergesort.mergesort(object.list);                  // line 85
}and
public class Mergesort
     public static void mergesort (int[] a)
          mergesort(a, 0, a.length-1);
     private static void mergesort (int[] a, int l, int r)
     private static void merge (int[] a, int l, int m, int r)
}Error:
Command.java:85: cannot find symbol
symbol : variable Mergesort
location: class Command
Mergesort.mergesort(object.list)
What am I doing wrong here? Within the Command class I am calling mergesort(), a static method, from a static method. I use the dot operator + object so that the compiler would recognize the 'list' array. I tried using the
Mergesort.mergesort(object.list);notation in hopes that it would work like this:
Class.staticMethod(parameters);but either I am mistaken, misunderstood the documentation or both. Mergesort is not a variable. Any help would be appreciated, I have been hitting a brick wall for hours with Java documentation. Thanks all.

[Javapedia: Classpath|http://wiki.java.net/bin/view/Javapedia/ClassPath]
[How Classes are Found|http://java.sun.com/j2se/1.5.0/docs/tooldocs/findingclasses.html]
[Setting the class path (Windows)|http://java.sun.com/j2se/1.5.0/docs/tooldocs/windows/classpath.html]
[Setting the class path (Solaris/Linux)|http://java.sun.com/j2se/1.5.0/docs/tooldocs/solaris/classpath.html]
[Understanding the Java ClassLoader|http://www-106.ibm.com/developerworks/edu/j-dw-javaclass-i.html]
java -cp .;<any other directories or jars> YourClassNameYou get a NoClassDefFoundError message because the JVM (Java Virtual Machine) can't find your class. The way to remedy this is to ensure that your class is included in the classpath. The example assumes that you are in the same directory as the class you're trying to run.
javac -classpath .;<any additional jar files or directories> YourClassName.javaYou get a "cannot resolve symbol" message because the compiler can't find your class. The way to remedy this is to ensure that your class is included in the classpath. The example assumes that you are in the same directory as the class you're trying to run.

Static method decisions

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