Static classes and variables

Hello,
I put all of my constants in an *{color:#3366ff}interface{color}* called Constants.java (I only put constants in this file) and when obfuscated the Constants.class file is removed from .jar and constants are inlined into classes this is Great! However, do I gain anything by placing all of my static methods into one class? Currently, there are all over the place and also I have classes that are already static like HttpMgr.java/ErrorMgr.java/InfoMgr.java I am thinking about merging these classes together with all static methods defined within the project. Do I gain or loss anything by doing this?
Thanks!

you will gain some bytes by merging all the static classes in one.
you can create a ManagerTool.java class and write inside all the static methods ...

Similar Messages

Static class and clustering

          I have a static class that I use to cache some values during a batch process. The
          batch process uses a JMS queue to parcel our identical units of work to MDBs.
          I want this to scale using a cluster with the same MDBs on multiple machines.
          Everything works fine except that I can't figure out how to tell my cache to clear
          itself out on every node between batch runs. Is there a pattern or solution to
          this problem?
          What I've tried is to create a stateless session bean method that clears my cache.
          At the begining of my batch job, (which is a stateless session bean call) I call
          this method on each server in the cluster by getting the remote interface for
          the stateless bean via the different URLs of the servers. However, the session
          bean method always executes on the one server where I make the call. It's as if
          WebLogic gives me back a local interface instead of the remote interface that
          I asked for.
          Any ideas would be appreciated.
          Colin


... static class and static method.I have never heard of a thing called "static class". Perhaps you mean a class with only static members?
My design approach (which is bound to needs of the moment and seldom to library-development or future re-use, since both is harder than most developers realize) is to develop straight without caring too much about static or not. When a method is done, debugged and works well, it happens that other objects access this method as well.
It may happen that I just want to use this single method and almost nothing else of the object. If that is the case, I can start looking if it's a Good Thing(tm) to make the method static, so no object creation is needed just for the one method. Sometimes it can be done, sometimes not.
But that's just me and you'll find quite a lot of coders that'll advice you to decide what's static and what not before you start coding. And that's as good an advice as most others you can get.
In the end it's your decision, so start fiddling around and see what fits best for you.
-T-

SQL, static classes and sessionBeans

Hi,
my JSF-project has one static class where it handle all sql-queries and I asked me if that is the "best" solution.
I.e. a User-Sessionbean call that static class to save his data into the user-sql-table. I asked myself, if it might not better to delete this static class and let the user-sessionbean save his data itself.
If my webserver has 100 usersessions and 50 users save their data at same time, does the "static-sql-save-version" has only one sql-connection and 49 user have to wait in a queue? And with the "every-usersession-has-his-own-sql-save-method" I have got 50 DB connection at the same time?
I hope you could help me :)
Alex

you will gain some bytes by merging all the static classes in one.
you can create a ManagerTool.java class and write inside all the static methods ...

Using java class and variables declared in java file in jsp

hi everyone
i m trying to seperate business logic form web layer. i don't know i am doing in a right way or not.
i wanted to access my own java class and its variables in jsp.
for this i created java file like this
package ris;
import java.sql.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class NewClass{
    public static void main(String args[]){
        Connection con = null;
        ResultSet rs=null;
        Statement smt=null;
        try{
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            con=DriverManager.getConnection("jdbc:mysql:///net","root", "anthony111");
            smt=con.createStatement();
           rs= smt.executeQuery("SELECT * FROM emp");
           while(rs.next()){
            String str = rs.getString("Name");
            }catch( Exception e){
                String msg="Exception:"+e.getMessage();
            }finally {
      try {
        if(con != null)
          con.close();
      } catch(SQLException e) {}
}next i created a jsp where i want to access String str defined in java class above.
<%--
    Document   : fisrt
    Created on : Jul 25, 2009, 3:00:38 PM
    Author     : REiSHI
--%>
<%@page import="ris.NewClass"%>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
   "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>JSP Page</title>
    </head>
    <body>
        <h1><%=str%></h1>
    </body>
</html>I wanted to print the name field extracted from database by ResultSet.
but it gives error cannot find symbol str.
please help me to find right way to do this.
i am using netbeans ide.

Very bad approach
1) Think if your table contains more than one NAMEs then you will get only the last one with your code.
2) Your String is declared as local variable in the method.
3) You have not created any object of NewClass nor called the method in JSP page. Then who will call the method to run sql?
4) Your NewClass contains main method which will not work in web application, it's not standalone desktop application so remove main.
Better create an ArrayList and then call the method of NewClass and then store the data into ArrayList and return the ArrayList.
It should look like
{code:java}
package ris;
import java.sql.*;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class NewClass{
    public static ArrayList getNames(){
        Connection con = null;
        ResultSet rs=null;
        Statement smt=null;
        ArrayList nameList = new ArrayList();
        try{
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            con=DriverManager.getConnection("jdbc:mysql:///net","root", "anthony111");
            smt=con.createStatement();
           rs= smt.executeQuery("SELECT * FROM emp");
           while(rs.next()){
            nameList.add(rs.getString("Name"));
           return nameList;
            }catch( Exception e){
                String msg="Exception:"+e.getMessage();
               </code><code class="jive-code jive-java"><font>return nameList;</code><code class="jive-code jive-java">
            }finally {
      try {
        if(con != null)
          con.close();
      } catch(SQLException e) {}
      </code><code>return nameList;</code>
<code class="jive-code jive-java">    }

"Static" class and application server

Hi, i have a little problem. I need to load a "static" class of a web application, deployed on Bea WebLogic 7 (or Tomcat), when the application server is starting.
Is it possible ? If yes, how can i do ?
Thanks

Yes, It's call from a servlet and the servlet is loaded on start up.
But I have resolved my problem this morning, however thanks for help. :)
Claudio

Difference between a static class and singleton

What is the difference between a static object and a singleton ?
for example:
1 )
public class MyObject {
static MyObject singleton ;
public static MyObject getInstance() {
if (singleton ==null) singleton = new MyObject ();
return singleton;
private MyObject () {
supe();
public void myMethod() {
2 )
public class MyObject {
private MyObject () {
supe();
public static void myMethod() {
If I need to call the myMethod() , witch of this solution is better ?
// case 1
MyObject.getInstance().myMethod()
// case 2
MyObject.myMethod()
.....

This has been discussed a lot here.
Use the forum's search feature, or, since it's not necessarily reliable, use google.
For many intents and purposes, they're equivalent.
However, with a singleton you can implement an interface, and get polymorphic behavior. You can't do with with a class full of static methods (which, by the way, is NOT a static class).

Difference between static class and singleton?

Hi I wonder what could be the difference between static methods and singleton?
In singleton at any point of time there will be only one object existing in the JVM. We create singleton to avoid multiple object creation for that class.
If I make all the methods in the class as static also it does the same job. The memory will be allocated once. Even there wont be any object in this case, so time required for object creation also can be saved. looks like more efficient but still why need singleton?
This question is also posted in java programming forum. The thread is as follows:-
[Click on this to visit that thread |http://forum.java.sun.com/thread.jspa?threadID=5278517&tstart=0]
Edited by: murrayb9654 on Mar 25, 2008 8:20 AM

yawmark wrote:
Static class is a realization of singleton pattern.Not in any conventional sense.
~Especially since a static class is completely different from a class with all static methods.

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;
}

Dynamic names for class and variable

Hi Folks,
How do you make a new instance of a class with a dynamic name.
var dynamicname = new dynamicname()
i try something
var this["test"]:Class = new ["Test"]()
but offcourse its not this...
I need this couse i have a librairy with SWC fonts they are only reference.. I get the font name from a CSS file and after i need to make a instance of the SWC file so the font is embedded.
Thanks anyone who can help me!
Cheer, Michierl

Btw Murphy its not working......
var fontRef = Class(getDefinitionByName("Arial"));
var font = new fontRef();
trace(font);
The varibable definition not defined.
I have 5 fonts as SWC Files set as reference lib in flex.
But i dont wann to load all fonts yet cosue that will make my movie 200kb ... so i copy the fontname of the stylesheet and then make a instance of that font class.
But how? With yours it need already a refrences to that class.

Singleton pattern class and static class

Hi,
what is difference between the singleton pattern class and static class ?
in singleton pattern, we declare a static member[which hold one value at a time] ,static method[ which return static member value] and a private constructor[not allow to direct instantiation]. My words are -- as a singleton pattern we implement static class .
so can we say a singleton pattern is static class it means both are same or is any difference between these two ??

malcolmmc wrote:
On several occasions I've had to convert a static (never instanceated) class to a singleton type, for example because I realise I need an instance per thread, or I decide to make a program more modular, with more than one configuration.
I've never done the opposite.
So generally I favour the singleton if there any "state" involved, because it's more flexible in unanticipated directions. It also gives extra flexibility when building tests, especially if you program to an interface.Total agreement; if anything it is dead hard to override static method logic with mock code in unit tests (I had to do it by keeping the static methods in place but making them internally use a singleton instance of itself of which the instance variable could be overwritten with a mock implementation for unit testing purposes...).
'Static classes' and/or methods are great for very simple util functions, but I wouldn't use them for anything other than that.

Do Static Classes exist?

Does Java allow the creation of static classes, and if so does that mean an instance of the class cannot be created? I know that a class can have static methods that only access static instance variables, but I don't know if that means that the class itself is static. I ask because I realized that you can't declare a static class like "public static class A {...}"

@OP. An inner class can be declared to be static,but
top level classes can't be static.
But that doesn't mean the static inner class
can't be instantiated (which seems to be what the OP
is thinking of).That was an answer to the topic - "Do static classes exist?", and the question does also say:
"Does Java allow the creation of static classes, and if so does that mean an instance of the class cannot be created?"
So I thought that the OP also wanted to know if static classes existed.
Kaj

About static class

Dose Java has Static class?
What is diff between static class and a final class which all method are static in java?

Dose Java has Static class?yes, but only if the class is an inner class
a static inner class does not have a reference to its enclosing class - because of this, a static inner class cannot use this to access any instance variable of the enclosing class
however, a static inner may access all static variables of the enclosing class
What is diff between static class and a final class
which all method are static in java?a static inner class is linke any other class in java
a final class with static methods is like the java.lang.Math class - you cnnot subclass it and do normally not instantiate it
hope that helps
Harry

Static class

Hello
at the start of my programme I would like to store some valuse (the values are trhe user rights that will be read from the data base) these values will never change during the execution of the programme.
so I was told that the best is to create a static class ...
can any one post an example of static class and how to store the values inside
and how to read it back
or just any link that speak about this
thank you in advance.

yeah i understand the ?:;
my question was on the form of the newthe code checks to see if an instance of Example already exists, and if it does, it returns that. if not, it creates a new one first. theoretically, only one instance will ever exist, but in practice, this variant of the pattern isn't thread-safe. simplest singleton:
public class MySingleton {
private static MySingleton INSTANCE = new MySingleton();
private MySingleton() {}
public static MySingleton getInstance() {
return INSTANCE;
}still lazily-loaded, despite what people might tell you, since the class itself is only loaded when you first need it

What are the differences between attributes and variables?

I am trying to develop a firmer understanding of the difference between attributes and variables. I understand attributes are lexically scoped to a class and variables are lexically scoped to the enclosing block. The lifetime of an attribute is linked to a class' instance. What is the lifetime of a variable? What is the lifetime of variables declared in a script file's top-level?

It depend on whether the script is running in standalone mode or been called by others (library mode).
If running as standalone, the variable of the script in the top level exists until the the script exit. If run as library mode, the variable in the top level of the script will never get to execute. Only the function and class available for call.
Try calling another script with top level variable (place print statement to verify), you realize in library mode, it will never been called. That's why the main method as in Java is never needed because of this reason.

What is static class ?

I know about static function.
What is static class?
What is the use of static class?
how can i use static class.?
Give me a static class example?

Static class and singleton are similar but they are not the same. A singleton is instantiated, and you have a reference to it - just one single reference no matter how many times you instantiate it. Singletons are good for data storage, config settings, loggers things that you may need all around your application, but you always want the same one.
A static class is not instantiated - an example of this is Flash's Math class. You can just do Math.sin() and get a result, you don't instantiate it in order to use it. Static classes are good for utility classes... essentially they are simply a namespace for a group of methods.
Oh, and you said you know about static function - what is static class - a static class then is just one that contains only static functions/methods.

Static classes and variables

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