Final static method
I have a class as follows that I instantiate in another program by:
CalcsLin calcsLin=new CalcsLin();
and use like:
r=calcsLin.tunits(r,2,4);
We obviously need "final static" on conv[ ], but I have not used it on tunits().
My questions are: What does "final static" do on tunits()?
Is it good to use it?
And does each usage still get its own separate copy of "f" and "i"?
public class CalcsLin {
final static double conv[] = { 12.0, 30.0, 24.0, 60.0, 60.0, 100.0 }; //example numbers only
final static double tunits(double r, int levfr, int levto) {
double f=1.0;
if(levfr<=levto) {
for(int i=levfr;i<=levto-1;i++)f=f*conv; r=r*f;
} else {
for(int i=levto;i<=levfr-1;i++)f=f*conv[i]; r=r/f;
} return(r);
Have you read the links I posted?
Static means that that method is part of the class, and not part of an object of that class.
Both will work, but first is preferred:
CalcsLin.tunits(1,2,3);
c = new CalcsLin();
c.tunits(1,2,3);And yes, it will work if you left static out, but I think it's in the right place there.
Besides that I realized too late that I only answered the first question, here are the other answers.
2nd: It is good to use it if (and only if) it makes sense. For example the [Math-class|http://java.sun.com/javase/6/docs/api/java/lang/Math.html]: the value of log(42) does not rely on any instance of the Math-class (if it was possible to instantiate this class) but is always the same equation, in those cases static functions are usefull. To make a static-method final isn't very usefull because the best way to call a static method is with it's class-name (thus CalcsLin.tunits(1,2,3); and not c = new CalcsLin(); c.log(1,2,3)).
3rd: Yes, every call of the method will have it's own 'instance' of f and i.
Similar Messages
-
Static Methods with all Final Parameters
Gurus,
I know the synchronization and static method question has been hashed out ad infinitum here. However, I was thinking of a slight twist. (Did a search but could not find something related to this. If this has already been posted, my apologies).
Suppose you have a static method in which all of the parameters in the method signature are declared final. Let's assume also that you are not performing an operation with a high latency (say, database or network operations).
Would it be "safe" to leave the static method unsynchronized in a multi-threaded environment? Would the final keyword(s) ensure that, throughout method execution, there is no longer a race condition?
Would there be a difference between a primitive:
static final public void doSomething(final int param) {}
And an object that has mutator methods:
static final public void doSomething(final List param) {}
Basically, not having a formal CS background, I'm not sure how static methods are actually invoked on a low-level. It probably varies across JVM's, and maybe this question doesn't make much sense. However, I thought I would throw this out to see if anyone had implemented something similar.
I might be giving "final" too much credit., but what would actually happen in a multi-threaded environment?
Thanks much!
- Saish
"My karma ran over your dogma." - AnonI know the synchronization and static method question
has been hashed out ad infinitum here. What question's that then?
Suppose you have a static method in which all of the
parameters in the method signature are declared final.
Let's assume also that you are not performing an
operation with a high latency (say, database or
network operations).
Would it be "safe" to leave the static method
unsynchronized in a multi-threaded environment?Whether or not the parameters are final makes no difference - method parameters are local to the method and so are only visible to the current thread anyway. So making them final will have no effect on anything goning on in any other thread.
Whether or not you are performing operations has no effect on whether or not you can call a method thread-safe. It might mean there is less contention and it might make race conditions less likely, but it won't eliminate them.
So the answer is: If your would be thread safe with non-final parameters, then it will still be thread-safe when the parameters are all final. If it is not thread-safe with non-final parameters, then it will still not be thread safe with final parameters.
Would the final keyword(s) ensure that, throughout
t method execution, there is no longer a race
condition?No. Absoloutely not. -
Thread Safety : Marking arguments of static method as final
Hi,
I have a class with static method. This class will be hit by several threads and I need to make the code thread safe. If I declare the arguments of this method as "final", will it guratnee that these variables cannot be changed by another thread calling this method?
Thanks in advance,
RtamehNo, the only condtion where parameters or local variables might be shared with another thread is if you create a local class which uses them, and the compiler won't allow you to do that if they aren't final.
Local variables are always thread-safe. -
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! -
OOPs Concept ! - Why Static Methods can't be redefined in its subclass ?
Dear Experts ,
I had searched the SDN , but unable to find out the satisfactorily answers ..
Can anybody let me know the reason for the following Confusion in Oops Concept
Question 1: As we know , We can Inherit the Static Methods in the Sub Class , But we can't redefine it in the base class or Sub Class ?
Question 2 : Why can't Static Method be Abstract ?
Question 3 : Can a Class be Abstract or Final Both, If yes, then why ?
Thanks in Advance
Saurabh GoelAs per the above discussion two of your doubts have already been clarified so I am taking only third one.
A class cannot never be Abstract and final both coz Abstract signifies that the implementation of the class has not been defined completelyi.e. may be some methods have been defined but few methods are still missing implementation. 'Final' is used for those classes/methods which cannot be redefined means the complete implementation of the method has been defined no one can implement further logic under the same method.
If you are saying your method is Final then it cannot be overridden and Abstract implies that method implementation is yet to be defined which can only be implemented if that class/method is not 'Final'. So both the terms are contradictory.
Hope it clarifies!!!
Thanks,
Vishesh -
Is creating a static method frowned upon in OO development? Is it only a matter of convenience by not having to instantiate?
Any insight is appreciated.
--Gregory
quote: Don't throw away the old bucket until you know whether the new one holds water.Regardless of how many objects you have created, there is only 1 copy of the static variables in the memory. Its not just a matter of convenience but is used in certain conditions based on some requirements. A good example would be Singleton. There already is a kind of Singleton class in the standard Java class libraries:
the Math class. This is a class that is declared final and all methods are declared static, meaning that the class cannot be extended. The purpose of the Math class is to wrap a number of common mathematical functions such as sin and log in a class-like structure, since the Java language does not support functions that are not methods in a class. You can use the same approach to a Singleton pattern, making it a final class. You can�t create any instance of classes like Math, and can only call the static
methods directly in the existing final class.
Another approach, suggested by Design Patterns, is to create Singletons using a static method to issue and keep track of instances. To prevent instantiating the class more than once, we make the constructor private so an instance can only be created from within the static method of the class.
Hope that helps
♠ -
How to determine the Class of a static methods class?
hi,
is there a way to get the code below to output
foo() called on One.class
foo() called on Two.classthanks,
asjf
public class Two extends One {
public static void main(String [] arg) {
One.foo(); // should say "foo() called on One.class"
Two.foo(); // should say "foo() called on Two.class"
class One {
public static final void foo() {
System.out.println("foo() called on "/*+something.getClass()*/);
}- One.class won't resolve to Two.class when the static
method is called via the class TwoThat's because static methods are not polymorphic. They cannot be overridden. For example try this:
public class Two extends One {
public static void main(String [] arg) {
One.foo(); // should say "foo() called on One.class"
Two.foo(); // should say "foo() called on Two.class"
One one = new Two();
one.foo();
((Two) one).foo();
public static void foo() {
System.out.println("foo() called on Two");
class One {
public static void foo() {
System.out.println("foo() called on One");
} -
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. -
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 advanceDefine them once (as final) in an abstract class. Then any subclass can call logError etc.
Kind regards,
Levi -
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. -
Memory management with static methods
I made a class with no attributes and only static methods with the purpose of maintaining as little as possible about it in memory. What information is kept in memory by the JVM about such a class ?
Thanx in advance :)Static methods don't consume less memory than regular instance
methods. Well, not exactly: a regular method requires a reference
to an instance as a hidden additional parameter. Thus, specifying
static for methods that don't access the object may actually save
a few bytes. However, the code is not duplicated for each instance.
Additionally, the JVM must keep any initialization values and the
names of the class and the methods, as needed by reflection.
Given suitable debugging options, local variables names and line
number may be kept in memory as well. Finally, all hosekeeping
info (gc, references and the like) must be kept in memory. -
What's the better approach for utility methods:
a) write abstract class with static methods
b) write class with non-static methods and instantiate this class to call the public methods.
?What's the better approach for utility methods:Define "utility methods".
a) write abstract class with static methodsProbably not - surely a final class would be better than an abstract one?
b) write class with non-static methods and instantiate
this class to call the public methods.Do you (or might you ever) want to be able to plug in different implementations? If so, then this is the better option. If not, then a final class with all methods static will probably do the job very well. -
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 paint cannot be referenced from static context
i cant seem to figure out this error dealing method paint:
public class TemplateCanvas extends Canvas implements Runnable {
//static
public static final int STATE_IDLE = 0;
public static final int STATE_ACTIVE = 1;
public static final int STATE_DONE = 2;
private int width;
private int height;
private Font font;
private Command start;
private int state;
private String message;
public TemplateCanvas() {
width = getWidth();
height = getHeight();
font = Font.getDefaultFont();
//// set up a command button to start network fetch
start = new Command("Start", Command.SCREEN, 1);
addCommand(start);
public void paint(Graphics g) {
g.setColor(0xffffff);
g.fillRect(0, 0, width, height);
g.setColor(0);
g.setFont(font);
if (state == STATE_ACTIVE) {
Animation.paint(g);
} else if (state == STATE_DONE) {
g.drawString(message, width >> 1, height >> 1, Graphics.TOP | Graphics.HCENTER);
public void commandAction(Command c, Displayable d) {
if (c == start) {
removeCommand(start);
//// start fetching in a new thread
Thread t = new Thread(this);
t.start();
public void run() {
state = STATE_ACTIVE;
//// start network fetch
Network network = new Network();
network.start();
//// start busy animation
Animation anim = new Animation(this);
anim.start();
//// wait for network to finish
synchronized (network) {
try {
wait();
} catch (InterruptedException ie) { }
//// end animation
anim.end();
//// get message from network
message = network.getResult();
//// repaint message
state = STATE_DONE;
repaint();
}TemplateCanvas.java:38: non-static method paint(javax.microedition.lcdui.Graphics) cannot be referenced from a static contextAnimation.paint(g); paint() is not a static method. That means you have to call it on an instance of an Animation class (an object), not on the class itself. This is designed this way because the paint() method uses variables that have to be instantiated, so if you don't have an instance to use, it can't access the variables it needs. Static methods don't use instance variables, they only use what's passed in to them, so they don't need to be called on an object. Hope that was clear.
-
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() {
}
Maybe you are looking for
-
Parameters in the SQL statement.
Hi I am creating a PL/SQL report. The report has for example 3 columns say X,Y,Z. When i run the report, i have 2 non-mandatory parameters P1 and P2. My question is, If i enter a value in the parameter P1, then the where condition of the report shoul
-
I would like to upgrade hard drive and start with clean OS how is this done?
I have a mac book pro and would like to install a new hard drive with the latest OS. I dont care about previous data just a clean start. What is then best method to this approach? Thanks!!
-
Acrobat X Pro (Mac) - Where do I find my custom dynamic stamps?
Running on Mavericks (OSX 10.9.3), Acrobat X (10.1.1) I've added a custom stamp and now trying to make it "dynamic" by editing it with Javascript. However the stamp file is no where to be found. I've done some research and already tried looking at th
-
Help with Syngery - copy/paste
I have two computer set up, windows and mac - they are sharing keyboard and mouse using syngery. I have the keyboad and mouse plugged into the windows box - I am using the mac keyboard. When I try and copy/pate on a mac I get ç √ those funny things.
-
Can we change the name of reassign button in sharepoint 2010 approval workflow?
can we change the name of reassign button in sharepoint 2010 approval workflow? Shazil Ali