Singleton class with static method

Hi,
I have made a fairly simple singletion class STClass. EX:
Consider tow cases
CASE-1:
private static STClass singleInstance;
private static int i;
private STClass()
public static STClass instance()
     if (singleInstance == null)
          singleInstance = new STClass();
          loadConfigFile("XYZ");
     return singleInstance;
private static void loadConfigFile(String fileName)
     //SOME CODE in which use private variable "i"
CASE-2:
private static STClass singleInstance;
private int i;
private STClass()
     loadConfigFile("XYZ");
public static STClass instance()
     if (singleInstance == null)
          singleInstance = new STClass();
     return singleInstance;
private void loadConfigFile(String fileName)
     //SOME CODE in which use private variable "i"
What is the differnce between two case and which one will be best and why???
Someone told me "If u keep variables and methods as static the the whole purpose of singleton class is defeated"
please justify this statement

It seems to me that this way should be more "correct":
public class STClass {
private static STClass singleInstance;
private int i;
private STClass() {
public static STClass getInstance() {
if (singleInstance == null) {
singleInstance = new STClass();
singleInstance.loadConfigFile("XYZ");
return singleInstance;
private void loadConfigFile(String fileName) {
//SOME CODE in which use private variable "i"
}And it is also compatible with your CASE-2.
Hope this helped,
Regards.I wouldnot agree with this piece of code here because of JMM bug. check this
http://www.javaworld.com/jw-02-2001/jw-0209-double-p2.html
What about proposing your own version, explained ?...

Similar Messages

What's the differences between a singleton and a class with static methods

Hi everybody.
My question is in the subject. Perhaps "differences" is not the good word. The positive and negative points ?
Imagine you have to write a connection pool, sure you gonna choose a singleton but why ?
Thank you very much.

A class is a class. Java doesn't have (and I wish it
did) a static outer class. Any class can extend
another class or implement an interface.A Class object cannot extend or implement anything - it is not under programmer control in any way. You can create a class which implements interfaces, but calling static methods is completely unrelated. Interfaces only affect instance methods, not class ones. I think all of your comparison to C++ is actually confusing you more. In Java, there is a real class object at runtime, as opposed to C++.
YATArchivist makes a good point about being able to
serialize, altho I've not met that desire in practice.
Maybe a concrete example would help.
mattbunch makes another point that I don't understand.
A class can implement an interface whether it sticks
its data in statics or in a dobject, so I guess I
still don't get that one.See my comment above. Static methods are free from all contractual obligations.
I prefer instance singletons to singleton classes because they are more flexible to change. For instance I created a thread pool singleton which worked by passing the instance around, but later I needed two thread pools so I made a slight modification to the class and poof! no more singleton and 99% of my code compiled cleanly against it.
When possible, I prefer to hand the instance off from object to object rather than have everything call Singleton.instance() since it makes changes like I mentioned earlier more feasible.

Singleton bottleneck with static methods?

A discussion came up at work today. If a class is created as a Singleton and only provides static methods and only final static data members (just for storing read only info like a connection string), will this create a bottleneck? Someone was suggesting that sharing the Singleton would cause each thread accessing the code to have to obtain the monitor on the class before being able to execute the method. Is this the case? None of the methods are synchronized, but they all perform atomic functionality. Anyone have any input on this?

Currenlty, it is implemented as a Singleton, part of
the discussion was moving everything into static
methods. Aside from that, the question is still
whether having a single location to run methods from
will become a bottleneckWho came up with the idea that this would create some sort of bottleneck? Never pay attention to them again.
Static methods are (slightly) faster than ordinary instance methods because there is no virtual method lookup. The only way there would be some sort of performance implication is if the methods are synchronized. In that case performance will be essentially the same as synchronized instance methods of a singleton.

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;
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GenericSet<T> g = assign(z);
Vector v = g.getVector();
if (!member(g,i))
v.addElement(i);
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GenericSet<T> g = assign(z);
Vector v = g.getVector();
if (member(g,i))
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return g;
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Vector v = z.getVector();
return v.contains(i);
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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 );
 }

In which case we need a class with all methods defined as abstract ?

In which case we need : A class with all methods defined as abstract (or should we go for Interface always in this case)

The concept of interface and abstract class overlaps sometime, but we can have the following thumb rule to use them for our specific need:
1) Interface: This should be use for code structuring. They standardize your application by providing a specific contract within and outside. If you think abstract class also provide structure, then reconsider as it limits the structure re-usability when there are many super-classes to inherit from. Java allow multiple inheritance by interface and not by Abstract class.
2) Abstract Class: This should be use for code-reusability. Interface doesn't have any code so can't be used for code-reusability.
Actually we can use both to provide the best.Taking a refernce to J2EE framework, the "Servlet" is an interface. It laids down the contract/structure for any code to be a servlet.
But the "GenericServlet" class is an abstract class which provides implementation of some of the methods defined in the "Servlet" interface and leave some method abstract.
Thus we see that the "Servlet" interface standardise the structure and the "GenericServlet" abstract class gives code re-usability.
Original Question:
In which case we need a class with all methods defined as abstract ?To this question, as all methods are abstarct we don't have option for code-reusability. so why not add standard structure concept to your application. So if there is not any restriction on making the field variable(if any) as final, we should go with the interface concept.

Testing ActionScript classes with native methods?

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I have an ActionScript class that I'm writing and would like to test using FlexUnit.
The only issue is that the ActionScript class has a member in it that is a class with native methods.
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VerifyError: Error #1079: Native methods are not allowed in loaded code.
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Hi casdvm,
by definition, you only own objects that you created using one of the alloc* methods, copy: or new:. All other objects (IIRC with a few noted exceptions) are autoreleased.
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Use of Synchronised with Static methods in EJBs

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Whether or not a method (static or non-static) is thread-safe depends on whether or not the method accesses instance and/or class variables or only method-local variables...
dave horner wrote:
We have a number of classes whose static methods are called by multiple EJBs. Could you tell me whether I might need to Synchronise these static methods or will this be unnecessary because they are being called by an EJB for a specific user.
Thanks
Dave

Enhanced SAP class with new methods - Not showing these from standard task

Dear Gurus,
I have enhanced SAP standard class with new methods. After I have activated my new methods and would like to create a workflow task using these new methods. when I create a task and input object category as "ABAP Class" and object type is SAP enhanced class. When I try to drop down for methods SAP is not showing my new methods. I do not know why. Am I missing any? Any help would be appreciated.
Note: Remember I am trying to use SAP ABAP class custom methods.
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Hi,
Your thread has had no response since it's creation over
2 weeks ago, therefore, I recommend that you either:
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- Close the thread if the answer is already known.
Thank you for your compliance in this regard.
Kind regards,
Siobhan

Creation of a static class with private methods

I'm new to java programming and am working on a project where I need to have a static class that does a postage calculation that must contain 2 private methods, one for first class and one for priority mail. I can't seem to figure out how to get the weight into the class to do the calculations or how to call the two private methods so that when one of my other classes calls on this class, it retrieves the correct postage. I've got all my other classes working correct and retrieving the information required. I need to use the weight from another class and return a "double". Help!!!
Here's my code:
* Title: Order Control 
* Description: Order Control Calculator using methods and classes
* Copyright: Copyright (c) 2002
* Company: Info 250, sec 001, T/TH 0930
* @author Peggy Blake
* @version 1.0, 10/29/02
import javax.swing.*;
public class ShippingCalculator
static double firstClass, priorityMail;
//how do I get my weight from another class into this method to use??? not sure I understand how it works.
public static double ShippingCalculator(double weight)
String responseFirstClass;
double quantity, shippingCost;
double totalFirstClass, firstClass, priorityMail, totalShipping;
double priorityMail1 = 3.50d;//prioritymail fee up to 1 pound
double priorityMail2 = 3.95d;//prioritymail fee up to 2 pounds
double priorityMail3 = 5.20d;//prioritymail fee up to 3 pounds
double priorityMail4 = 6.45d;//prioritymail fee up to 4 pounds
double priorityMail5 = 7.70d;//prioritymail fee up to 5 pounds
quantity = 0d;//ititialization of quantity
// weight = 0d;//initialization of weight
// shippingCost = 0d;
//calculation of the number of items ordered..each item weights .75 ounces
quantity = (weight/.75);
if (quantity <= 30d)
//add 1 ounce to quantities that weigh less than 30 ounces
weight = (weight + 1);
else
//add 2 ounces to quantities that weigh more than 30 ounces
weight = (weight + 2);
if (weight > 80d)
//message to orderclerk ..order over 5 lbs, cannot process
JOptionPane.showMessageDialog(null, "Order exceeded 5 lbs, cannot process");
//exit system, do not process anything else
System.exit (0);
else
if (weight < 14d)
//send message to customer: ship firstclass or priority, y or n
responseFirstClass = JOptionPane.showInputDialog(null, "Ship first class? y or n?");
if (responseFirstClass.equals("y"))
//compute FirstClass shipping cost
totalFirstClass = ((weight - 1) * .23d) + .34d;
firstClass = totalFirstClass;
else
//compute PriorityMail cost for orders less than 14 ounces
priorityMail = (priorityMail1);
else
if (weight <=16d)
//compute totalshipping for orders up to 16 ounces
priorityMail = (priorityMail1);
else
if (weight <=32d)
//compute totalshipping for orders up to 32 ounces
priorityMail = (priorityMail2);
else
if (weight <=48d)
//compute totalshipping for orders up to 48 ounces
priorityMail = (priorityMail3);
else
if (weight <= 64d)
//compute totalshipping for orders up to 64 ounces
priorityMail = (priorityMail4);
else
//compute totalshipping for orders up to 80 ounces
priorityMail = (priorityMail5);
priorityMail = 0d;
firstClass = 0d;
firstClassMail ();
priorityMailCost ();
//I think this is where I should be pulling the two methods below into my code, but can't figure out how to do it.
shippingCost = priorityMail + firstClass;
return (shippingCost);
}//end method calculate shipping
private static double firstClassMail()//method to get first class ship cost
return (firstClass);
}//end method firstclass shipping
private static double priorityMailCost()//method to get priority mail cost
return (priorityMail);
}//end method priorityMail
}//end class shipping calculator

public class A {
public String getXXX () {
public class B {
A a = new A();
public void init () {
a.getXXX();
}

How to get the class name static method which exists in the parent class

Hi,
How to know the name of the class or reference to instance of the class with in the main/static method
in the below example
class AbstA
public static void main(String[] args)
System.out.println(getXXClass().getName());
public class A extends AbstA
public class B extends AbstA
on compile all the class and run of
java A
should print A as the name
java B
should print B as the name
Are there any suggestions to know the class name in the static method, which is in the parent class.
Regards,
Raja Nagendra Kumar

Well, there's a hack you can use, but if you think you need it,Could you let me the hack solution for this..
you probably have a design flaw and/or a misunderstanding about how to use Java.)May be, but my needs seems to be very genuine..of not repeat the main method contents in every inherited class..
The need we have is this
I have the test cases inheriting from common base class.
When the main method of the test class is run, it is supposed to find all other test cases, which belong to same package and subpackages and create a entire suite and run the entire suite.
In the above need of the logic we wrote in the main method could handle any class provided it knows what is the child class from which this main is called.
I applicate your inputs on a better way to design without replicating the code..
In my view getClass() should have been static as the instance it returns is one for all its instances of that class.
I know there are complications the way compiler handles static vars and methods.. May be there is a need for OO principals to advance..
Regards,
Raja Nagendra Kumar
Edited by: rajanag on Jul 26, 2009 6:03 PM

Nested Classes and Static Methods

I was perusing the Java Tutorials on Nested Classes and I came across this...
[http://java.sun.com/docs/books/tutorial/java/javaOO/nested.html|http://java.sun.com/docs/books/tutorial/java/javaOO/nested.html]
I was reading the documentation and I read a slightly confusing statement. I was hoping some further discussion could clarify the matter. The documentation on "Nested Classes" says (I highlighted the two statements, in bold, I am having trouble piecing together.)
Static Nested Classes
As with class methods and variables, a static nested class is associated with its outer class. And like static class methods, a static nested class cannot refer directly to instance variables or methods defined in its enclosing class ? it can use them only through an object reference.
Note: A static nested class interacts with the instance members of its outer class (and other classes) just like any other top-level class. In effect, a static nested class is behaviorally a top-level class that has been nested in another top-level class for packaging convenience.
So this means a nested static inner class CANNOT refer to its own instanced variables, like a normal static method, but CAN refer to its outer class instanced variables?

So this means a nested static inner class CANNOT refer to its own instanced variables, like a normal static method, but CAN refer to its outer class instanced variables?No, it means that a static nested class cannot refer to instance variables of its enclosing class. Example:public class Foo {
    int i;
    static class Bar {
        int j = i; // WRONG! Bar class is static context
}~

Abstract Method in a Class with implemented method

I have a class which already has methods Implemented.I mean thse metgods are not abstract.I want only one method to be abstarct which will be overrideen by its subclass or derived Class
I have never tried this
Does anyone knows how to do this
If yes could you give me syntax of the method
Thanks in advance
CSJakharia

javax.swing.JComponent is an example of an abstract
class with no abstract methods. That is why the
following works:
JComponent component = new JComponent(){};
Not to forget you cannot instantiate abstarct classes
public abstract class Test
public String getName()
return "Mike";
public static void main(String[] args)
Test tt = new Test();
System.out.println(tt.getName());
}and you would get the error
The type Test cannot be instantiated.
You remove the abstract keyword and it would compile
good.No I am not misinterpreting I know what he is saying but I am closing the door of misinterpretation which I felt was possible. ;)
cheers

EasyMock 1.2 - working with static methods

Hi,
I'm working in an application which was written in java1.4. So we are using EasyMock 1.2 version since higher versions doesn't support java 1.4. I need to expect and return an array for a static method which is in a Util class (No interfaces involved). How can i do it with EasyMock 1.2?
Any help would be much appreciated. Thanks.
Edited by: user10996478 on Feb 28, 2012 7:06 AM

If the guide doesn't explain it:
http://easymock.org/EasyMock1_2_Java1_3_Documentation.html
Then you have no choice but to use the source code of the API as the manual I'm afraid. I wouldn't hold my breath that you get help using a third party API which is incredibly outdated. The website mentions some yahoo group, perhaps you should attempt to see if it is still available and you can join it.

What's wrong with static methods?

Answers on an postcard please.

I think the point here is that sometimes people come from a procedural background (or maybe no background) and they start with main, and one static method leads to another. They reach a tipping point where they are reluctant to define non-static methods to a class because it's all static elsewhere. And static method can't access instance data, so their data becomes largely static as well. When the dust settles, they are programming procedually in Java. So too many static methods is a sign that you may be programming procedurally instead of doing OOP, but using static appropriately is still cool.
And let's not get pedantic. What goes wrong if I make my String class's getLength method static?
public final class MyString {
    private int length;
    public static int getLength(String s) {
        return s.length;
}It's a misuse of static, but it doesn't break my design.

Interface with static methods

I'm writting a wrapper for exception handling.One of the classes uses log4j to log exceptions.I want to write a interface to generalize loggin.Idealy I should have an interface with certain static methods for loging (i.e logError,logDebugMessage,consoleError,consoleMessage,etc) , but Interface dosent allow that and neither do abstract classes can havstatic method declarations.The implementations of these methods will achieve the hiding of the complexity of using a logging package,log levels etc from the user.
Let me know how best I can work something out for this.
Thanks in advance

Define them once (as final) in an abstract class. Then any subclass can call logError etc.
Kind regards,
Levi

Singleton class with static method

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