Static Block vs Static Method

Hi,
what is the diff. b/w declaring the variable inside the static block vs static method?
Why static block is executed first before static method?
Once the class has been loaded inside the memory the static block will automatically executed by the compiler & it will executed before any static methods. What is the reason behind this why? static block is executed before static method? Please do provide an answer for this..
Thanks,
JavaLover

Um.
A static method is like a regular method; it only gets called if its...called.
public class Test
static
     //this stuff executes after being loaded into memory
public static void main(string args[])
    //this main method is executed by the VM when you execute "java Test"
    staticMethod(); // this makes the program call staticMethod();
public static void staticMethod()
    //this code wouldn't be executed if main(string[]) hadn't called it.
}Hope everything I've said here is correct.

Similar Messages

Initializer block not called when static method called

public class Initializer {
     Initializer(){
          System.out.println("Constructor called");
               System.out.println("CLASS INITIALIZED");
     static void method(){
          System.out.println("Static method called");
     public static void main(String[] args) {
          Initializer.method();
From the JLS
A class or interface type T will be initialized immediately before the first occurrence of any one of the following:
T is a class and an instance of T is created.
T is a class and a static method declared by T is invoked.
[b]
But when i call the static method , if the class is initialized shouldnt the initializer block be called, it is not called, why.

Perhaps running something like this will add a little more colour?:
public class Initializer {
    static {
        System.out.println("First static initializer");
        System.out.println("First instance initializer");
    Initializer() {
        System.out.println("Constructor");
    static {
        System.out.println("Second static initializer");
        System.out.println("Second instance initializer");
    static void staticMethod() {
        System.out.println("staticMethod");
    void instanceMethod() {
        System.out.println("instanceMethod");
    public static void main(String[] args) {
        System.out.println("main");
        staticMethod();
        new Initializer().instanceMethod();
}

No warning for 'name clash' of static methods

The background is that I am trying to design a package which allows conversion methods to be 'plugged-in' to a class within a class hierarchy so that users can choose how objects are converted to double values. (For example, a 'city-block' conversion might be used instead of the Euclidean-distance one for class TwoD below.) I am trying to use generics to ensure that only converters specific to the appropriate class can be 'plugged-in' and also to simplify the definition of new converters.
The issue that has arisen is a case which is not 'type-safe', in that the behaviour is not what I would expect from the type specifications, yet no warning is given. The full code is below.
public abstract class Base {
    public abstract Converter getConverter();
    public double convert() {
        return this.getConverter().convert(this); // produces a warning
public class OneD extends Base {
    static Converter<OneD> converter;
    int x;
    public OneD(int x) {
        this.x = x;
    public static void setConverter(Converter<OneD> c) {
        converter = c;
    public Converter getConverter() {
        return converter;
public class TwoD extends OneD {
    static Converter<TwoD> converter;
    int y;
    public TwoD(int x, int y) {
        super(x);
        this.y = y;
    public static void setConverter(Converter<TwoD> c) {
        converter = c;
    }                                   // compiles OK with no warning
    public Converter getConverter() {
        return converter;
public abstract class Converter<T> {
    public abstract double convert(T val);
public class OneDConverter extends Converter<OneD> {
     public double convert(OneD val) {
        return val.x;
public class TwoDConverter extends Converter<TwoD> {
    public double convert(TwoD val) {
        return Math.sqrt(val.x * val.x + val.y * val.y);
public class Test {
    public static void main(String[] args) {
        OneD x1d = new OneD(1);
        TwoD x2d = new TwoD(1, 1);
        OneD.setConverter(new OneDConverter());
        TwoD.setConverter(new TwoDConverter());
        System.out.println("Convert OneD(1): " + x1d.convert() +
                           ", Convert TwoD(1, 1): " + x2d.convert());
        TwoD.setConverter(new OneDConverter());
          // wrong type of converter; should not be allowed
        System.out.println("Convert OneD(1): " + x1d.convert() +
                           ", Convert TwoD(1, 1): " + x2d.convert());
}This produces the output:
Convert OneD(1): 1.0, Convert TwoD(1, 1): 1.4142135623730951
Convert OneD(1): 1.0, Convert TwoD(1, 1): 1.0The first line of this shows that the all is working OK, but in the second line we see that the wrong type of converter has been plugged-in to class TwoD, with no complaints or warnings at compile or run-time. I understand why this is so (as a result of erasure), but I am surprised that no warning is given that the static method setConverter() in class TwoD clashes with the one in OneD. Is this really type-safe behaviour? (If the two methods are made instance methods instead of static, the code does not compile because of a 'name clash' error.)
Incidentally, an 'unchecked warning' arises because of the use of the raw class Converter in class Base, but I cannot figure out how to avoid this. The warning is right, and signals that we cannot be sure that the converter is the appropriate type for the argument. It is up to subclasses to ensure this and I cannot figure out how to guarantee that it will be so.

public abstract class Base {
public abstract Converter getConverter();
public double convert() {
return this.getConverter().convert(this); // produces a warning
}Some of the problems you're seeing can be resolved
by organizing your code better:
abstract class Base<T extends Base<T>> {
    public abstract Converter<T> getConverter();
    public double convert() {
        return this.getConverter().convert(getThis());
    abstract protected T getThis();
class OneD extends Base<OneD> {
    static Converter<OneD> converter;
    int x;
    public OneD(int x) {
        this.x = x;
    public static void setConverter(Converter<OneD> c) {
        converter = c;
    public Converter<OneD> getConverter() {
        return converter;
    protected OneD getThis() { return this; }
class TwoD extends Base<TwoD> {
    static Converter<TwoD> converter;
    int y;
    int x;
    public TwoD(int x, int y) {
        this.x = x;
        this.y = y;
    public static void setConverter(Converter<TwoD> c) {
        converter = c;
    public Converter<TwoD> getConverter() {
        return converter;
    protected TwoD getThis() { return this; }
abstract class Converter<T> {
    public abstract double convert(T val);
class OneDConverter extends Converter<OneD> {
     public double convert(OneD val) {
        return val.x;
class TwoDConverter extends Converter<TwoD> {
    public double convert(TwoD val) {
        return Math.sqrt(val.x * val.x + val.y * val.y);
class Test {
    public static void main(String[] args) {
        OneD x1d = new OneD(1);
        TwoD x2d = new TwoD(1, 1);
        OneD.setConverter(new OneDConverter());
        TwoD.setConverter(new TwoDConverter());
        System.out.println("Convert OneD(1): " + x1d.convert() +
                           ", Convert TwoD(1, 1): " + x2d.convert());
        TwoD.setConverter(new OneDConverter()); // error
        System.out.println("Convert OneD(1): " + x1d.convert() +
                           ", Convert TwoD(1, 1): " + x2d.convert());
}

Need some explanations regarding static Method

Hello,
I have a code where a class has a static method access by other classes. This not working as I thought and I would like to understand why.
Here below is the code.
Here is a class having the static method "test"
package test;
public class StaticTest {
    public StaticTest() {
    public static void test (int i){
    while (i < 1000){
        System.out.println("i = " + i );
        i++;
}Here is the code of another class (Thread) using this static method. This Thread can be initialized with an integrer value that will be passed to the static Method.
package test;
public class ThreadTester extends Thread {
    int x;
    public ThreadTester(int i) {
        x=i;
    public void run(){
        StaticTest.test(x);
}Here is the code starting 2 Thread running in parallel and both are then calling the static method.
//start 2 thread accessing the static method.
      ThreadTester test1 = new ThreadTester(0);
      ThreadTester test2 = new ThreadTester(200);
      test1.start();
      test2.start();
...As the second thread is started with a bigger value I thought that we would only have seen few printouts from the first thread starting by 0 and then printouts starting by 200.
Here is what I thought regarding the result:
i = 0
i = 1
i = 2
i = 3
i = 200 --> startup of the second thread, x in static method is overriden (at least this is what I thought!)
i = 201
i = 202
i = 203
i = 204
i = 205
i = 206
i = 207
i = 208
i = 209
But the real result is:
i = 0
i = 1
i = 2
i = 3
i = 4
i = 5
i = 200
i = 6
i = 201
i = 202
i = 203
i = 204
i = 205
i = 206
i = 7
i = 207
i = 208
i = 209
i = 8
It seems that there is 2 instances running in parallel. I thought that it would'nt be the case with the word "Static".
Also I don't understand the result because if I use JBuilder in Optimizer mode I can see that there is only one instance of StaticTest object.
Can anyone here explain me how is that possible?
Thanks in advance for your help.
Regards,
Alain.

>
thread test1 creates its own stack and starts incrementing �i� starting at values 0. However, in the middle of incrementing, it gets kicked out by the OS (or JVM) into a �blocked� state to allow other threads to run. BUT before leaving the running state, test1 saves the stack state including the value of �i�.
>
Ok, now I understand, but then I have another question.
What is the difference between the code shown in my first post and the following where we create 2 instances of StaticTest class (which is not static in this case for sure).
How to decide (while coding) if it is better to use difference instances of class or not?
package test;
public class StaticTest {
    public StaticTest() {
    public void test (int i){ //Not static anymore
    while (i < 1000){
        System.out.println("i = " + i );
        i++;
}We create new instance in the Thread.
package test;
public class ThreadTester extends Thread {
    int x;
    public ThreadTester(int i) {
        x=i;
    public void run(){
StaticTest newInstance = new StaticTest(); //Create a new instance
        newInstance .test(x);
}Alain

Why there should not be many static methods.

Why a java class should not have many static methods.How is memory managed in case of static methods.
If a Utility class has static methods then we can use methods directly by class name but if we do not make the methods static then we can acess methods using object.How does it make the difference.I know that there remains a single copy of class variables/methods.But i want to know how class memory is managed and garbage collected.

shobhit123 wrote:
Why a java class should not have many static methods.How is memory managed in case of static methods.
If a Utility class has static methods then we can use methods directly by class name but if we do not make the methods static then we can acess methods using object.How does it make the difference.I know that there remains a single copy of class variables/methods.But i want to know how class memory is managed and garbage collected.The reason to discourage static methods is stylistic rather than technical. It encourages object oriented thinking.
Each loaded class is represented by a Class object, and associated with that it a block of memory for static fields. As with all such storage this block is, as viewed from code, rather like an array with one, or in the case of double or long values, two slots per field.
Because the class loader maintains a map from FQN to Class this storage is only released if the class loader that loaded it becomes unreachable, which happens only in situations like the un-deployment of a web application or EJB.
Local variables for static methods are allocated in a stack frame, just as with instance methods. There's really no significant difference there.

Are Static methods Thread safe?

Hello All
I have a static method that takes a integer and returns a mathematically processed result.
Since this method is frequently required, I have placed it in a common class and declared it as static.
I want to know whether this method is thread safe?

There's nothing special about static methods, with regard to thread safety. If they access shared objects, then such access will usually need to be controlled by synchronisation; this might be on the object being accessed, some higher-level object or a special object allocated purely as a lock. The only way that you might think of them as special is that there's no instance of the Class on which you can synchronise.
You can declare a static method as synchronised. If you do, it will be synchronised on the single Class object of the class in which it is declared. This means that only one thread can be executing any part of the method at any one time. However, I understand that the Java Runtime itself sometimes synchronises on this Class object for its own reasons, therefore you might sometimes find a synchronised static method blocks when no other thread is executing it. Usually better, therefore, to explicitly synchronise on some object or other, than to use synchronised static methods.

Can I have a static method?

I want to know whether we can have static method and static block in Ejb.
also I want to know the use of these and when these will be invoked by the container

Technically speaking you can have static methods or static blocks the java compiler or teh ejb deployer will not complain
However its always a good practice to avoid having static blocks, static methods in EJB
if you have the urge to initialise or have a startup code in your application when EJB is loaded , you can implement the code in ejbCreate()
- I dont see any other reason where you might need static block
if there is any other reason please explain what cirumstances drives you to have static {} static mthd()
if it is statess session Bean avoid having even non-static member variables
Reasons for not having non-static member variable in Stateless Session EJB is
1. stateless EJBs are pooled so the instances are pooled after use.. so there is a chance you might get the same instance with previous assigned values
Hope the info helps!

Interesting Qtion: Synchronize a static method

I know that a non-static method and a block can be synchronized.
Can anyone tell me as to what it means to synchronize a static method of a class and how/when is it used. I just tried compiling the code and it gives no compiler/syntactical errors.
it would be helpful if u could take up a simple class example.
Thanks,
Novice

Hi,
A good example for using synchronized static methods is the singleton pattern. E.g.
public class Singleton
private Singleton() {}
private static Singleton fgUniqueInstance;
public static synchronized Singleton getInstance()
    if (fgUniqueInstance==null) {
      fgUniqueInstance = new Singleton();
    return fgUniqueInstance;
}If you won't synchronize this class in a multi-threading environment, it could happen, that more than one instance is created.
Andre

When a static method is accessed concurrently

When a static method is accessed by many objects symultaneously(concurrently),
What is happened in the static method.
Are the stacks for that method maded seperately and
each stack doesn't influence other stacks?
thank you in advance.

The static objects or methods concept is clear, one
instance for all objects.No. One instance for the class.
, and every
one know that, static methods is slower than
nonstatic, Since when? I've certainly never heard that before... Do you have a reference I can look at?
and this is as i thought because static
methods are syncronized by default.Absoloutely not!
All synchronization locks on an object. When you synchronize an instance method, it locks on the implicit "this"; When you synchronize a static method, it locks on the class's associated Class object.
So two synchronized static methods in the same class can not be called at the same time, but synchronized instance methods that access static variables can all access those variables at the same time and potentially cause threading problems. In this situation you can declare the static fields volatile or wrap synchronized blocks around all code that accesses them, and synchronize on the same object (perhaps the Class object associated with the current class would be appropriate, but that reallt depends on the rest of your design).

Static method vs synchronisation

Hi,
A fundamental query.
If i am declaring a method as static, can i also declare it as sunchronized? i.e. can i have something like
public static synchronized sss(){
xxx
If a method is static, there is only one instance in the memory. Correspondingly, only one client can execute it at a time. in which case it is automatically synchronized.
Pl correct my reasoning.
When do we have the requirement of having a static method, or probably a singleton??
Thanks,
Prashant Gupta

Hi,
A fundamental query.
If i am declaring a method as static, can i also declare it as sunchronized? i.e. can
i have something like
public static synchronized sss(){
xxx
}?Yes, static methods can be synchronized which means that when any thread is running within a synchronized static method of class C, no other thread may enter a static synchronized method of that class. In other words, the monitor acquired by a static synchronized method is the Class itself while the monitor acquired by a non-static synchronized method is the object refered to by 'this'.
If a method is static, there is only one instance in the memory. Correspondingly,
only one client can execute it at a time. in which case it is automatically synchronized.There is (in most circumstances) a single copy of the definition (bytecodes representing all methods - static or not - and static fields) of of a class. However, any number of threads may be executing within any section of code unles that code is guarded by a synchronized block or within a synchronized method. In that case, no two threads can enter (well, actually be runnable within - Object.wait() has special implications) a synchronized block monitored by the same object.
When do we have the requirement of having a static method, or
probably a singleton??Not sure what you are asking here. You define static methods when there is behavior you want to implement that does not need to have access to instance (non-static) fields or methods and which would never need to be overridden (for purposes of polymorphism) by derived classes.
Wen needing a singleton, you have a choice of defining a "true singleton" (i.e. a class with a private constructor, some sort of static getInstance() method, with the bulk of its methods anf fields are non-static) or defining a class whose methods are all static and whose fields are also all static. Singletons. Use the one that fits you needs the best.
Chuck

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.

Static Block vs Static Method

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