Do static methods perform better
Sometimes, especially when refactoring (specifically when doing extract method), I create a method in a class to perform some helpful task or to neatly tuck a chunk of ugly code away somewhere that it can be easily referred to from the "actual" code. This new method doesn't actually directly cause a state change in the object, it just accepts a parameter and returns a value, or similar. In nearly every case this method is private (since it only helps out the class in which it appears).
I can easily declare these helper methods static, or leave them unstatic. What I'm wondering is if there's any best practice in doing one or the other, whether for performance reasons or otherwise. I'd tend not to make them static because it might imply that the method should be called from a static context or something, but I wondered what others suggest in this regard.
Thanks.
I agree with you Dubwai, and in practice will probably
not use static unless I mean it. But, since the
methods don't really act on any of the class's
instance members, I'm also not entirely convinced that
this does go against the "design" -- because
whether the method is static or not, it has the exact
same effect.
In fact, marking it static might even help make
it obvious that this method performs no side-effects
on instance members.
But again, I think I'll just leave them nonstatic.I'm not saying that you shouldn't make things static. Quite the contrary. I'm saying that things should be static if they are static, meaning they don't change polymorphically or per instance. If this is so, the method should definitely be static.
Not using instance members is a neccesary condition of being a static method but it is not nearly sufficient. Making a method static means throwing polymorphism out if the door. A method may do nothing but return a static final value but still need to be an instance method if a subclass needs to return a different static final value. If you make a method static and then need to refactor, it can be difficult or impossible to do so, as pointed out above. If you are calling static methods as if they are instance methods, that indicates to me that they probably should just be instance methods.
Similar Messages
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Help with JSP / Static methods in beans...
Hi:
I am creating several javabeans as part of my application. Is it ok, to make all of them static (no global variables are used) and access in JSP's and Servlets as XXBean.method(var1, var 1). Is this a problem ? (vs creating a new XXBean and using it in every page/servlet).
I have gut feeling that static methods are better and give better memory usage and performance - as oppose in other scenario I am creating a new Bean for every page access - could not verify. and not sure not creating (new Bean) would give any problems.
Thanks for sharing.No, static methods are not what you want. Just set the "scope" on your use-bean tag to "application".
<jsp:useBean id="xbean" class="xpackage.XXBean" scope="application" />Alternatively, if what you are trying to do is a pure "function library", then create a tag lib, and add the function definitions like this:
<function>
<name>someMethod</name>
<function-class>xpackage.XXBean</function-class>
<function-signature>
java.lang.String someMethod( java.lang.String )
</function-signature>
</function>There is a fairly concise description of how to do this at
http://java.boot.by/wcd-guide/ch07s04.html -
Using static methods in JavaBeans
Hi:
I am creating several beans as part of my application. Is it ok, to make all of them static (no global variables are used) and access in JSP's and Servlets as XXBean.method(var1, var 1). Is this a problem ? (vs creating a new XXBean and using it in every page/servlet).
I have gut feeling that static methods are better and give better memory usage and performance - as oppose in other scenario I am creating a new Bean for every page access - could not verify. and not sure not creating (new Bean) would give any problems.
Thanks for sharing.I think you mixed up JavaBeans and Enterprise JavaBeans (EJBs) ...
I think Sun Microsystems really named them badly ...
They are in fact totally different things ...
I agree with them.
Please read the tutorials first.
Asuka Kenji (UserID = 289)
(Duke Dollar Hunting now ...) -
Static method,new thread performance question
Hey guys i just have two questions about two methods used in many controllers/servlets in my app:
1-what is the difference between calling a static method in a util class or a non static method (like methods dealing with dates i.e getting current time,converting between timezones), which is better ? 2-what is the difference between calling a method(contain too many logic like sending emails) in the controller directly or running this method in a different thread ?cs.student wrote:
Hey guys i just have two questions about two methods used in many controllers/servlets in my app:
1-what is the difference between calling a static method in a util class or a non static method (like methods dealing with dates i.e getting current time,converting between timezones), which is better ?Depends on the design. It's impossible to say straight why one way would be better than another. Programming isn't that straight forward.
2-what is the difference between calling a method(contain too many logic like sending emails) in the controller directly or running this method in a different thread ?Threads can be run at the same time. So what you're asking is "what's the difference between doing one thing after another and doing two things at the same time". -
Which method is better to the performance?
Using SQLs at front side or using stored procedures at back side, which method is better to the performance?
jetq wrote:
In my view, it maybe have other difference, for example,
Using stored procedure, you don't need to recompile the script every time to be executed,
and use the existing execute plan.what if first time procedure is called after DB start?
PL/SQL does not have EXPLAIN PLAN; only SQL does.
But using SQL statement from application layer may be different.different than what exactly.
SQL is SQL & can only be executed by SQL Engine inside the DB.
SQL statement does not know or care about how it got to the DB.
DB does not know or care from where SQL originated. -
In terms of scalabilty, will static method in normal java class better than
You only have one copy of the static method in memory, but you have a few copy of the stateless session bean, plus the overhead of those session bean.So isn't static method of normal java class more scalable than stateless session bean.
Then you have to take care of transaction management, connection pooling, etc other ejb services all by your self.
In fact stateless session beans acts more like a static class. They do not get destroyed when remove() method is called on client stub. Similarly they are not always gets created whenever someone calls create() method on home interface!! (Again it's specific to appserver implementation)
Thx. -
Static method and variables doubts
i have a doubt
i have the following method
private static void checkActionType(String action) {
if (action.startsWith(" a")) {
++totalAddedActions;
} else if (action.startsWith(" c")) {
++totalChangedFolders;
} else if (action.startsWith(" p")) {
++totalPersonalizedActions;
} else if (action.startsWith(" r")) {
++totalRemovedActions;
} else if (action.startsWith(" v")) {
++totalViewedActions;
} else if (action.startsWith(" u")) {
++totalUpdateActions;
to use it, i need to declare my int variables static, because im calling this method from another static method that is called by main method.
but this can cause me problems ?
if i have two instances of this class running, my statics int will show the right value?
there is a better approach?Here is my class, i want some advices to know if i am doing right, because everything is a little new for me.
My class, read a log file and based upon a regular expression, it can retrieve a general statistic or a personal statistic.
package br.com.organox.aggregator;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.Vector;
import org.apache.oro.text.regex.*;
public class LogFileReader {
private static Pattern regexpPattern;
private static PatternMatcher patternMatcher;
private static PatternCompiler patternCompiler;
private static PatternMatcherInput patternInput;
private static MatchResult matchResult;
private static final String patternString = "^[^\']+User\\s+\'([^\']+)\'[^\']+session\\s+\'([^\']+)\'\\s+(\\S+)";
// Integers used to store number of user, sessions and specific actions
private static int totalUsers;
private static int totalSessions;
private static int totalAddedActions;
private static int totalChangedFolders;
private static int totalPersonalizedActions;
private static int totalRemovedActions;
private static int totalUpdateActions;
private static int totalViewedActions;
public static void main(String[] args) {
if (args.length == 0) {
System.out.println("No file name was specified");
printClassUsage();
} else if (args.length == 1) {
printGeneralData(args[0]);
} else if (args.length == 2) {
System.out.println("You must set file name, data value and data type in order to " +
"this class run properly");
printClassUsage();
} else {
printSelectedData(args[0],args[1],args[2]);
public static void printGeneralData(String fileName) {
String data = "";
//Users and the Session Vector are used to avoid count repeated values.
Vector usersVector = new Vector();
Vector sessionVector = new Vector();
patternCompiler = new Perl5Compiler();
patternMatcher = new Perl5Matcher();
try {
regexpPattern = patternCompiler.compile(patternString);
} catch (MalformedPatternException mpe) {
System.out.println("Error Compiling Pattern");
System.out.println(mpe.getMessage());
try {
FileReader fileRead = new FileReader(fileName);
BufferedReader buffRead = new BufferedReader(fileRead);
while ((data = buffRead.readLine())!= null) {
patternInput = new PatternMatcherInput(data);
while(patternMatcher.contains(patternInput,regexpPattern)) {
matchResult = patternMatcher.getMatch();
// Avoid to insert repeated data in user and session Vectors
if (usersVector.lastIndexOf(matchResult.group(1)) == -1) {
usersVector.add(matchResult.group(1));
if (sessionVector.lastIndexOf(matchResult.group(2)) == -1) {
sessionVector.add(matchResult.group(2));
increaseActionType(matchResult.group(3));
for (int i=0;i<usersVector.size();i++) {
totalUsers++;
for (int i=0;i<sessionVector.size();i++) {
totalSessions++;
fileRead.close();
buffRead.close();
} catch (IOException ioe) {
System.out.println("An I/O error occurred while getting log file data");
ioe.printStackTrace();
System.out.println("Users logged : " + totalUsers);
System.out.println("Sessions opened : " + totalSessions);
System.out.println("Added contents : " + totalAddedActions);
System.out.println("Changed folders : " + totalChangedFolders);
System.out.println("Personalized contents : " + totalPersonalizedActions);
System.out.println("Removed contents : " + totalRemovedActions);
System.out.println("Viewed Contents : " + totalViewedActions);
System.out.println("Updated contents : " + totalUpdateActions);
public static void printSelectedData(String fileName,String value,String valueType) {
String data = "";
String user = "";
//Flag used to print the right result on screen
String printFlag = "";
Vector sessionVector = new Vector();
Vector userVector = new Vector();
Vector actionVector = new Vector();
patternCompiler = new Perl5Compiler();
patternMatcher = new Perl5Matcher();
try {
regexpPattern = patternCompiler.compile(patternString);
} catch (MalformedPatternException mpe) {
System.out.println("Error Compiling Pattern");
System.out.println(mpe.getMessage());
try {
FileReader fileRead = new FileReader(fileName);
BufferedReader buffRead = new BufferedReader(fileRead);
while ((data = buffRead.readLine())!= null) {
patternInput = new PatternMatcherInput(data);
while(patternMatcher.contains(patternInput,regexpPattern)) {
matchResult = patternMatcher.getMatch();
if (valueType.equalsIgnoreCase("-user")) {
printFlag = "userPrint";
if ((matchResult.group(1).equalsIgnoreCase(value))) {
userVector.add(matchResult.group(1));
// avoid insert a repeated value inside session vector.
if (sessionVector.lastIndexOf(matchResult.group(2)) == -1) {
sessionVector.add(matchResult.group(2));
increaseActionType(matchResult.group(3));
if (userVector.size() == 0) {
printFlag = "userPrintError";
} else if (valueType.equalsIgnoreCase("-session")) {
printFlag = "sessionPrint";
if ((matchResult.group(2).equalsIgnoreCase(value))) {
user = matchResult.group(1);
sessionVector.add(matchResult.group(2));
increaseActionType(matchResult.group(3));
if (sessionVector.size() == 0) {
printFlag = "sessionPrintError";
} else if (valueType.equalsIgnoreCase("-action")) {
printFlag = "actionPrint";
if ((matchResult.group(3).equalsIgnoreCase(value))) {
if (userVector.lastIndexOf(matchResult.group(1)) == -1) {
userVector.add(matchResult.group(1));
actionVector.add(matchResult.group(3));
if (actionVector.size() == 0) {
printFlag = "actionPrintError";
fileRead.close();
buffRead.close();
} catch (IOException ioe) {
System.out.println("An I/O error occurred while getting log file data");
ioe.printStackTrace();
if (printFlag.equals("userPrint")) {
for (int i=0;i<sessionVector.size();i++) {
totalSessions++;
System.out.println("Sessions opened by user " + value + " : " + totalSessions);
System.out.println("Added contents by user " + value + " : " + totalAddedActions);
System.out.println("Changed folders by user " + value + " : " + totalChangedFolders);
System.out.println("Personalized contents by user " + value + " : " + totalPersonalizedActions);
System.out.println("Removed contents by user " + value + " : " + totalRemovedActions);
System.out.println("Viewed contents by user " + value + " : " + totalViewedActions);
System.out.println("Updated contents by user " + value + " : " + totalUpdateActions);
} else if (printFlag.equals("userPrintError")) {
System.out.println("This user " + value + " was not found on log file");
} else if (printFlag.equals("sessionPrint")){
System.out.println("Session " + value + " was opened by user " + user);
System.out.println("Added contents by session " + value + " : " + totalAddedActions);
System.out.println("Changed folders by session " + value + " : " + totalChangedFolders);
System.out.println("Personalized contents by session " + value + " : " + totalPersonalizedActions);
System.out.println("Removed contents by session " + value + " : " + totalRemovedActions);
System.out.println("Viewed Contents by session " + value + " : " + totalViewedActions);
System.out.println("Updated contents by session " + value + " : " + totalUpdateActions);
} else if (printFlag.equals("sessionPrintError")){
System.out.println("This session " + value + " was not found on log file");
} else if (printFlag.equals("actionPrint")){
System.out.println("Action " + value + " was performed " + actionVector.size() +
" times for " + userVector.size() + " different user(s)");
} else if (printFlag.equals("actionPrintError")){
System.out.println("This action " + value + " was not found on log file");
} else {
System.out.println("Wrong search type!");
System.out.println("Accepted types are: ");
System.out.println("-user -> Search for a specified user");
System.out.println("-session -> Search for a specified session");
System.out.println("-action -> Search for a specified action");
private static void increaseActionType(String action) {
if (action.startsWith("a")) {
++totalAddedActions;
} else if (action.startsWith("c")) {
++totalChangedFolders;
} else if (action.startsWith("p")) {
++totalPersonalizedActions;
} else if (action.startsWith("r")) {
++totalRemovedActions;
} else if (action.startsWith("v")) {
++totalViewedActions;
} else if (action.startsWith("u")) {
++totalUpdateActions;
} -
What 's the advantage of static method.
I think if a method is declared as static, the program should allocate some spaces for the method when the program start. However, I found many static method in an erp open source project. What make me confused is that it will cost many spaces.
Perhaps they want to lose some spaces for speed???
Can somebody answer my question.thanks!> I think if a method is declared as static, the
program should allocate some spaces for the method
when the program start. However, I found many static
method in an erp open source project. What make me
confused is that it will cost many spaces.
Perhaps they want to lose some spaces for speed???
Can somebody answer my question.thanks!
To be sincere, I've never thought about performance cost when static methods are used. I decide to create and use them mainly whether I have the "feeling" that it will provide me benefits, in terms of designing. Yes, it's like a feeling. I am not able to explain you why or how I have this feeling, I'm not native in English language, so choosing the appropriate words to explain my ideas sometimes is hard to me. Besides. I admit that I am a little bit lazy in this moment, I don't want to search through some dictionary...;-).
I think the more you develop your abilities and skills in java programming, the more you can feel, you can have this "feeling", and naturally you figure out in which situations using static methods is a better choice. -
will an application containing many static methods use more memory than an application w/ less static methods? are there any performance or memory issues w/ using static methods?
I totally disagree that one should let oop principles NOT performance dominate design. While you may have a point in 99.99% of applications, I am in the 0.01% where performance has forced me to implement some hard choices.
If static is faster and you call that method millions of time you may have some real issues to face. Let's say you lose a microsecond on each call by going non-static. That means for 1x10^6 calls you've lost a second. Which may not seem like a lot, but in multi-threaded user apps such as servers, this is very significant.
I'd argue that there shouldn't even be a method. In fact just expose the instance variables and access the data directly, or don't even have the class and just in-line. Or even better, jni. How about just write it in Assembler. Where to draw the line???
Before rants occur, this is only important to do in critical sections of code. Not recommended where you can use well structured oop principles which are preferred. -
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! -
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, thanksWhen 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! -
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 KumarWell, 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 -
Should I use a static method or an instance method?
Just a simple function to look at a HashMap and tell how many non-null entries.
This will be common code that will run on a multi-threaded weblogic app server and potentially serve many apps running at once.
Does this have to be an instance method? Or is it perfectly fine to use a static method?
public static int countNonNullEntries(HashMap hm){
if(hm==null)return 0;
int count=0;
for(int i=0; i<hm.size(); i++) {
if(hm.get(i)!=null)
{ count++;}
return count;
OR
public int countNonNullEntries(HashMap hm){
if(hm==null)return 0;
int count=0;
for(int i=0; i<hm.size(); i++) {
if(hm.get(i)!=null)
{ count++;}
return count;
}TPD Opitz-Consulting com wrote:
The question is the other way around: Is there a good reason to make the method static?
Ususally the answer is: no.The question is: does this method need state? Yes -> method of a class with that state. No -> static.
The good thing of having this method statig is that it meight decrese memory foot pring but unless you're facing memory related problem you should not think about that.I doubt there is any difference between the memory foot print of a static or not method.
I'm not shure if this method beeing static maks problems in multithreaded environments like the one you're aiming at. But I do know that an immutable object is always thread save.Does the method use shared state (data)? No -> no multi threaded problems.
Can the parameters be modified by different threads? Yes, if multiple threads modified the parameter map, but nothing you can do about it here (no way to force the calling thread to lock on whatever you lock on).
So my answer to your question is: yes, it should be non static.The method should be static since it uses no state.
It is thread-safe when only the calling thread can modify the passed map (using a synchronized or ConcurrentHashMap is not enough, since you don't call a single atomic method on the map).
// Better use Map instead of HashMap
// We don't care about the generic type, but that does not mean we should use a raw type
public static int countNonNullEntries(Map<?, ?> map) {
// whether to accept null map or not, no need for explicit exception
// since next statement throw NPE anyway
Collection<?> values = map.values();
// note your method is called countNonNull, not countNull!
// (original code it would need to by if(null != mapValue) notNullsCounter++;
return values.size() - java.util.Collections.frequency(values, null);
} -
Trying to understand Static methods
Hi all,
I am trying to learn a little bit about static methods and hope that someone here can help me understand it better. My understanding of static methods is that they exist only once (More like global methods). This tells me that usage of static methods should be used with care as they are likely to cause problems in cases where multiple users try to access a static object at the same time.
I am looking at a piece of code that had me thinking for a bit. I cant post the code itself but here is an example of how the code is structured
The first class declares a couple of non static arrays and makes them available via the getters and setters. It also has one method that calls a static method in another class.
package com.tests.statictest;
import java.util.ArrayList;
public class ClassA{
ArrayList arrayList1 = new ArrayList();
ArrayList arrayList2 = new ArrayList();
public ClassA(){
arrayList1.add("TEST1");
arrayList1.add("TEST2");
arrayList2.add("Test3");
arrayList2.add("Test4");
ArrayList getArrayList1(){
return arrayList1;
ArrayList getArrayList2(){
return arrayList2;
ArrayList getJoinedArrayList(){
return ClassB.joinArrays(arrayList1,arrayList2);
}The second class contains the static method that is called by the above class to join the two arrays. This class is used by many other classes
package com.tests.statictest;
import java.util.ArrayList;
public class ClassB{
public static ArrayList joinArrays(ArrayList list1, ArrayList list2){
ArrayList list3 = new ArrayList();
list1.addAll(list2);
return list1;
}And here is my test class
package com.tests.statictest;
public class ClassC{
public static void main(String args[]){
ClassA classA = new ClassA();
System.out.println(classA.getArrayList1());
System.out.println(classA.getArrayList2());
System.out.println(classA.getJoinedArrayList());
}The output to the above program is shown below
[TEST1, TEST2]
[Test3, Test4]
[TEST1, TEST2, Test3, Test4]My question for the above is that i am wondering if the above is safe. Can you think of situations where the above is not recommended. What exactly would happen if ten instances of ClassA threads are executed at the same time? Woulnt the static method in ClassB corrupt the data?ziggy wrote:
Hi all,
I am trying to learn a little bit about static methods and hope that someone here can help me understand it better. My understanding of static methods is that they exist only once (More like global methods). This tells me that usage of static methods should be used with care as they are likely to cause problems in cases where multiple users try to access a static object at the same time. There is no such thing as a "static object" in Java. The word "static" simply means "belonging to a class as a whole, rather than an individual instance."
My question for the above is that i am wondering if the above is safe. Can you think of situations where the above is not recommended. What exactly would happen if ten instances of ClassA threads are executed at the same time?ClassA isn't a thread, so it can't be "executed", per se.
Woulnt the static method in ClassB corrupt the data?"Staticness" doesn't have anything to do with it; the issue at hand is operations on a shared data structure, which is a concern whether you're dealing with static or non-static members. There is nothing inherent in ClassB that will "corrupt" anything, however.
~
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