Instantiating an object of a class using variable

Can anyone please tell me how to instantiate an object of a class, the class name is stored in string variable.
something like:
String s = "MyClass";
<s> anObj = new <s> ;
what will be the appropriate substitution of <s> ?

Orkay, Leave it up to u to learn the Exceptions that are gonna be thrown. Look up the APIs, Rather easy
String s = <fullyQualifiedClassName>;
try {
Class someClass = Class.forName(s);
Object instance = someClass.newInstance();
if (instance instanceof <someExpectedInstance>) {
<someExpectedInstance> x = (<someExpectedInstance>) instance;
} catch (Exception e) {
System.err.println(e.getMessage());
}Primarily look up the reflection API, and in particular Class.

Similar Messages

ActiveX in BradySoft (CodeSoft) - What Class/Method/Object's would I use to send variable form data to BradySoft?

What Class/Method/Object's would I use to send variable form data to BradySoft? I have a basic label setup in BradySoft and I want to send it variable form data (a serial number) from Labview ActiveX. I have attached Brady's ActiveX programmers guide but can't figure out what to use for this. P.S. I would call Brady or TekLynx tech support about this but they have a strict policy whereas BradySoft supports ActiveX but their tech support doesn't provide programming help with it. I figured I'd try the NI Forums.

Aaronb, I presume by publishing an ActiveX programmers manual the BradySoft software installs Active X objects. You may choose to interact with these objects within LabVIEW using Active X controls. The following link will provide a starting point for LabVIEW help topics on Active X communication: Select ActiveX Object Dialog Box
http://zone.ni.com/reference/en-XX/help/371361F-01/lvdialog/insert_active_x_object/
Building a Simple Web Browser Using ActiveX (Example of ActiveX arcitecture)
http://zone.ni.com/devzone/cda/epd/p/id/81 Hope this helps provide a bit of guidance. Cheers!

Using variable of one class in another class

what are the different ways in which we can access a variable defined in one class in some other class ,i am aware of making object of that class and using variable ,inheritance polymorphisms,is there any other way

learnerpuneet wrote:
i don't want to use objects of the respective class to access methods and variablesSo you've given up on OO already?
Well okay, then declare everything static and you can use class names to access methods and variables.

How to make an object of inner class and use it ?

Hi tecs,
In my JSF application i have a need to make an inner member class in one of my bean class.
How can i make the object of this class?(what should be the entry in faces-config)
And there are text box and check box (in the JSP) associated with the elements of this inner class. What should be the coding in JSP so that elements in the JSP can be linked with the corresponding members of the inner class ?
Plz help.
Thnx in advance.

Hi
I am havin 10 text boxes in my application.
But out of 10 , 3 will be always together(existence of one is not possible without the other two.)
Now i want to create a vector of objects ( here object will consist of the value corresponding to these three boxes),there can be many elements in this vector.
So i m thinking to make an inner class which have three String variables corresponding to these text boxes that exists together.
What can b done ?

Tool to create Java Object classes using the Database Tables

Hi,
Is their any tools or utility available to create the Java Object Classes using the Database Tables as input.
Lets Say I am having the Employee, Employee_Salary tables in the Database.The utility has to create the Java Object classes with the relation.
Please Help...
Thx..

Hm, for generating regular Java classes I wouldn't know one from memory. But I suggest you start searching in for example the Eclipse marketspace for a third party plugin that can do it. If all fail, you could always use Hibernate Tools from the Jboss Tools Eclipse plugin set to generate Hibernate/JPA entities and then strip the annotations from them to turn them into regular POJO classes.
How many tables are we talking about anyway? It might be less effort to just create the classes with properties and then use an IDE to generate getters and setters for them.

Instantiation an inner class using reflection

I want to instantiate an inner class using the Class.newInstance() method called within the Outer class constructor:
public Outer
public Outer()
Inner.class.newInstance();
private Class Inner { }
When I try it, however, I get an InstantiationException.
Is there some way to do this?
Thanks for the help.
Scott

Here is a consolidation of what everyone posted and it does appear to work. In one of your post you used the getDeclaredConstructors() method and said it was less than ideal; I am not sure what you meant but I suspect it was the hard coded array reference. Anyhow I used the getDeclaredConstructor() method which appears to get non-public constructors also and is basically the same as using the getConstructor() method.
import java.lang.reflect.*;
public class Test35 {
    static public void main(String[] args) {
        Test35 t35 = new Test35();
        t35.testIt();
    private class Inner {
        public String toString() {
            return "Hear I am";
    public void testIt() {
        try {
            Constructor con = Inner.class.getDeclaredConstructor(new Class[] {Test35.class});
            Inner in = (Inner)con.newInstance(new Object[] {this});
            System.out.println(in);
        } catch (Exception e) {
            e.printStackTrace();

Help with Declaring a Class with a Method and Instantiating an Object

hello all i am having trouble understanding and completing a lab tutorial again!
im supposed to compile an run this code then save work to understand how to declare aclass with a method an instantiate an object of the class with the following code
// Program 1: GradeBook.java
// Class declaration with one method.
public class GradeBook
// display a welcome message to the GradeBook user
public void displayMessage()
System.out.println( "Welcome to the Grade Book!" );
} // end method displayMessage
} // end class GradeBook
// Program 2: GradeBookTest4.java
// Create a GradeBook object and call its displayMessage method.
public class GradeBookTest
// main method begins program execution
public static void main( String args[] )
// create a GradeBook object and assign it to myGradeBook
GradeBook myGradeBook = new GradeBook();
// call myGradeBook's displayMessage method
myGradeBook.displayMessage();
} // end main
} // end class GradeBookTest4
i saved above code as shown to working directory filename GradeBookTest4.java
C:\Program Files\Java\jdk1.6.0_11\bin but recieved error message
C:\Program Files\Java\jdk1.6.0_11\bin>javac GradeBook4a.java GradeBookTest4.java
GradeBookTest4.java:2: class, interface, or enum expected
^
GradeBookTest4.java:27: reached end of file while parsing
^
2 errors
can someone tell me where the errors are because for class or interface expected message i found a solution which says 'class? or 'interface' expected is because there is a missing { somewhere much earlier in the code. i dont know what "java:51: reached end of file while parsing " means or what to do to fix ,any ideas a re appreciated

Doesn't solve your problem, but this works for me...
public class GradeBook
public void displayMessage() {
    System.out.println( "Welcome to the Grade Book!" );
public static void main( String args[] ) {
    try {
      GradeBook gradeBook = new GradeBook();
      gradeBook.displayMessage();
    } catch (Exception e) {
      e.printStackTrace();
}

Class/member variables usage in servlets and/or helper classes

I just started on a new dev team and I saw in some of their code where the HttpSession is stored as a class/member variable of a servlet helper class, and I was not sure if this was ok to do or not? Will there be problems when multiple users are accessing the same code?
To give some more detail, we are using WebLogic and using their Controller (.jpf) files as our servlet/action. Several helper files were created for the Controller file. In the Controller, the helper file (MyHelper.java) is instantiated, and then has a method invoked on it. One of the parameters to the method of the helper class is the HttpServletRequest object. In the method of the helper file, the very first line gets the session from the request object and assigns it to a class variable. Is this ok? If so, would it be better to pass in the instance of the HttpServletRequest object as a parameter to the constructor, which would set the class variable, or does it even matter? The class variable holding the session is used in several other methods, which are all invoked from the method that was invoked from the Controller.
In the Controller file:
MyHelper help = new MyHelper();
help.doIt(request);MyHelper.java
public class MyHelper {
    private HttpSession session;
    public void doIt(HttpServletRequest request) {
        session = request.getSession();
        String temp = test();
    private String test() {
        String s = session.getAttribute("test");
        return s;
}In the past when I have coded servlets, I just passed the request and/or session around to the other methods or classes that may have needed it. However, maybe I did not need to do that. I want to know if what is being done above will have any issues with the data getting "crossed" between users or anything of that sort.
If anyone has any thoughts/comments/ideas about this I would greatly appreciate it.

No thoughts from anyone?

Help: Factory Class using Inner Class and Private Constructor?

The situation is as follows:
I want a GamesCollection class that instantiates Game objects by looking up the information needed from a database. I would like to use Game outside of GamesCollection, but only have it instantiated by GamesCollection to ensure the game actually exist. Each Game object is linked to a database record. If a Game object exist, it must also exist in the database. Game objects can never be removed from the database.
I thought about making the Game object an inner class of GamesCollection, but this means that Game class constructor is still visible outside. So what if I made Game constructor private? Well, now I can't create Game objects without a static method inside Game class (static Object factory).
Basically what I need is a constructor for the inner Game class accessible to GamesCollection, but not to the rest of the world (including packages). Is there a way to do this?

leesiulung wrote:
As a second look, I was initially confused about your first implementation, but it now makes more sense.
Let me make sure I understand this:
- the interface is needed to make the class accessible outside the outer classBetter: it is necessary to have a type that is accessible outside of GameCollection -- what else could be the return type of instance?
- the instance() method is the object factory
- the private modifier for the inner class is to prevent outside classes to instantiate this objectRight.
However, is a private inner class accessible in the outer class? Try it and see.
How does this affect private/public modifiers on inner classes?Take about five minutes and write a few tests. That should answer any questions you may have.
How do instantiate a GameImpl object? This basically goes back to the first question.Filling out the initial solution:
public interface Game {
    String method();
public class GameCollection {
    private static class GameImpl implements Game {
        public String method() {
            return "GameImpl";
    public Game instance() {
        return new GameImpl();
    public static void main(String[] args) {
        GameCollection app = new GameCollection();
        Game game = app.instance();
        System.out.println(game.method());
}Even if you were not interested in controlling game creation, defining interfaces for key concepts like Game is always going to be a good idea. Consider how you will write testing code, for example. How will you mock Game?

Accessing the same object from multiple classes.

For the life of me I can't workout how I can access things from classes that haven't created them.
I don't want to have to use "new" multiple times in seperate classes as that would erase manipulated values.
I want to be able to access and manipulate an array of objects from multiple classes without resetting the array object values. How do I create a new object then be able to use it from all classes rather than re-creating it?
Also I need my GUI to recognize the changes my buttons are making to data and reload itself so they show up.
All help is good help!
regards,
Luke Grainger

As long as you have a headquarters it shouldn't be to painfull. You simply keep a refrence to your ShipDataBase and Arsenal and all your irrellevant stuff in Headquarters. So the start of your Headquarters class would look something like:
public class Headquarters{
public Arsenal arsenal;
public ShipDatabase db;
//constructor
public Headquarters(){
    arsenal = new Arsenal(this, ....);
    db = new ShipDatabase(...);
//The Arsenal class:
public class Arsenal{
public Headquarter hq;
public Arsenal(Headquarter hq, ....){
    this.hq = hq;
    .Then in your ShipDatabase you should, as good programing goes, keep the arraylist as a private class variable, and then make simple public methods to access it. Methods like getShipList(), addToShipList(Ship ship)....
So when you want to add a ship from arsenal you write:
hq.db.addToShipList(ship);
.Or you could of course use a more direct refrence:
ShipDatabase db = hq.db;
or even
ShipList = hq.db.getShipList();
but this requires that the shiplist in the DB is kept public....
Hope it was comprehensive enough, and that I answered what you where wondering.
Sjur
PS: Initialise the array is what you do right here:
//constructor
shipList = new Ship[6];
shipList[0] = new Ship("Sentry", 15, 10, "Scout");
" " " "etc
shipList[5] = new Ship("Sentry", 15, 10, "Scout");PPS: To make code snippets etc. more readable please read this article:
http://forum.java.sun.com/faq.jsp#messageformat

ABAP Objects with Workflows / Classes and Instances

Hello,
I am currently designing a workflow using an ABAP-Objects. So far I have been been able to get my Workflow to run with my class, but I have a couple of problems:
- I am using the Function 'SAP_WAPI_START_WORKFLOW' to start other subflows, which enables me to decide which subflow to start at runtime. All of the subflows have standart importing-parameters in their containers, such as the key of my class. In each workflow I instantiate my class using a self-written method, which checks the table T_INSTANCES in my object, and then either returns the object reference to an existing instance or creates a new one. Obviously all of the subflows that I call from my main workflow should be able to find the instance. As far as I can see in their protocolls, this happens without any problems. The problem starts when I make changes to the instance. For example the changing of attributes (with setter methods) seems not to work. After the subflows are finished, in my main workflow, I do not see (with getter methods) any changes that has been made to the object. Is local persistence really limited to one workflow ?
- My second problem is basically about the workflow container in workflow protocoll. In the same workflow, I can change the attributes of my object. Nevertheless, the protocoll always show the initial attribute, even though, my task with the getter-method returns the new value of the attribute.
I appreciate any help and thanks a lot in advance.

Hello Pauls,
Thank you for your answer. I think we are misunderstanding each other. The problem occurs (I think) because my class is not a singleton class. Or am I mistaken ?
When I directly start a subflow from my main workflow, then the instance that I have created in my main workflow is also visible to the subflow. As well as the static table which actually keeps track of the instances. So, in this case the subflows finds the instance and then can use the object as is.
When I start a subflow from my main workflow using the function I mentioned above, then even though the same object key is used, there is a new instance. And the static table (I assume that you mean a static variable from type table, when you say "class table") is completely empty. In this case, my "new" instance is created which overwrites every attribute that I have set in the main workflow, before I started the subflow. More interestingly, my main workflow instantiates another new object, as soon as the subflow has finished. (I am using an event to wait for the subflow to finish.)
On the other hand, I am not quite sure that I understood your approach with refresh and how it could help me. This method is not well documented anywhere, and all of the examples that I have found are about "leave it empty"
As far as I understood, this method is called by the workflow between the steps, when an object is used. I slowly start to think that I need advanced information about Workflows and Memory Management.
Thanks a lot again. Apparently, I am the only person who came across such a problem
Greetz
G.Fendoglu

Casting base class object to derived class object

interface myinterface
     void fun1();
class Base implements myinterface
     public void fun1()
class Derived extends Base
public class File1
     public myinterface fun()
          return (myinterface) new Base();
     public static void main(String args[])
          File1 obj = new File1();
          Derived dobj = (Derived)obj.fun();
Giving the exception ClassCastException......
Can't we convert from base class object to derived class.
Can any one help me please...
Thnaks in Advance
Bharath kumar.

When posting code, please use tags
The object returned by File1.fun() is of type Base. You cannot cast an object to something it isn't - in this case, Base isn't Dervied. If you added some member variables to Derived, and the compiler allowed your cast from Base to Derived to succeed, where would these member variables come from?
Also, you don't need the cast to myinterface in File1.fun()
Also, normal Java coding conventions recommend naming classes and interfaces (in this case, myinterface) with leading capital letters, and camel-case caps throughout (e.g. MyInterface)

How to instantiate class using GUID field from a table

Hi,
There is a class ' /MRSS/CL_SGD_COMPLEX_DEMAND ' and method /MRSS/IF_SGE_COMPLEX_DEMAND~ITEMS_GET.
Actual requirement is field called GUID from the table instantiate the class and i can use its methods to get the reference to assign object.

If i understand the requirement correctly , you need to perform items_get based on the guid. Then create the constructor with a parameter for your GUID , then store this guid in a class member variable. And then you can use the same in the ITEMS_GET( ).
Regards
Kavindra

Get session object in a class

hi,
is possible obtain the session object in a class method without send it from jsp as a parameter?

you mean like this?
     public ActionForward execute(
          ActionMapping mapping,
          ActionForm form,
          HttpServletRequest req,
          HttpServletResponse res)
          throws Exception {
          SessionManager sm = new SessionManager(req);
                                ....sessionmanager class
package com....;
import java.util.*;
import java.lang.reflect.*;
import java.io.*;
import javax.servlet.*;
import javax.servlet.jsp.*;
import javax.servlet.http.*;
import org.apache.log4j.*;
* <code>SessionManager</code> is a wrapper for request, response and session
* @author
public class SessionManager {
     static Logger log = Logger.getLogger(SessionManager.class);
     ** Holds string containing the unique identifier assigned to this session
     private String sessionid;
     ** Holds HttpSession object
     private HttpSession session;
     ** Holds request object object - must be passed in by the calling application
     private HttpServletRequest request;
     ** Holds response object - any application sending a response must call
     ** session manager
     private HttpServletResponse response;
     ** Holds Servlet Context - useful if logging is reqd.
     private ServletContext context;
      * Page context.
     private PageContext pctx = null;
     ** Constructor to initialize with a request object
     public SessionManager(HttpServletRequest req) {
          request = req;
          session = req.getSession();
          sessionid = session.getId();
     ** Constructor to initialize with a pagecontext object - convenient to call from jsp's
     public SessionManager(PageContext pctx) {
          request = (HttpServletRequest) pctx.getRequest();
          response = (HttpServletResponse) pctx.getResponse();
          context = pctx.getServletContext();
          session = pctx.getSession();
          sessionid = session.getId();
          this.pctx = pctx;
     ** Constructor to initialize with request, response objects
     public SessionManager(HttpServletRequest req, HttpServletResponse resp) {
          request = req;
          response = resp;
          session = req.getSession();
          sessionid = session.getId();
     ** Constructor to initialize with request, servletcontext objects
     public SessionManager(HttpServletRequest req, ServletContext ctx) {
          request = req;
          context = ctx;
          session = req.getSession();
          sessionid = session.getId();
     ** Constructor to initialize with request, response and context objects
     public SessionManager(HttpServletRequest req, HttpServletResponse resp, ServletContext ctx) {
          request = req;
          response = resp;
          context = ctx;
          session = req.getSession();
          sessionid = session.getId();
     ** Setter and getter methods
     public void setRequest(HttpServletRequest req) {
          request = req;
          session = req.getSession();
          sessionid = session.getId();
     ** Setter and getter methods
     public void setContext(ServletContext ctx) {
          context = ctx;
     ** Setter and getter methods
     public ServletContext getContext() {
          return context;
     public void createLoginSession(java.io.Serializable obj) {
          if (obj == null)
               log.debug("Object is null");
          setAttribute("user", obj);
     public void setAttribute(String key, java.io.Serializable obj) {
          session.setAttribute(key, obj);
     public void removeAttribute(String key) {
          session.removeAttribute(key);
     ** Setter and getter methods
     public HttpServletRequest getRequest() {
          return request;
     ** Setter and getter methods
     public HttpServletResponse getResponse() {
          return response;
     ** Checks if either member session or guest session exists
     public boolean isLoggedIn() {
          if (session.getAttribute("user") != null)
               return true;
          else
               return false;
     public long getCreationTime() {
          return session.getCreationTime();
     ** Setter and getter methods
     public String getId() {
          return session.getId();
     public long getLastAccessedTime() {
          return session.getLastAccessedTime();
     public int getMaxInactiveInterval() {
          return session.getMaxInactiveInterval();
     ** Setter and getter methods - also useful for retrieving state object(s)
     public Object getAttribute(String name) {
          if (session != null)
               Object sObject = session.getAttribute(name);
               //Log.debug("Session State for the object "+name+" is "+sObject);
               return sObject;
          else
               return null;
     ** Setter and getter methods - gets enum of all stored state objects
     public Enumeration getAttributeNames() {
          return session.getAttributeNames();
     public void invalidate() {
          session.invalidate();
          // Remove all object that is bound to this session
          //wip : Resetting instance variable.
          //This is necesary as further operations on session will
          //result in illegalstateexception
          session = null;
     public boolean isNew() {
          return session.isNew();
     public void setMaxInactiveInterval(int interval) {
          session.setMaxInactiveInterval(interval);
      * This method returns the host url in the form "www.carclub.com".
      * <p>
      * The return value is compatible with default_website field of clubs DB table.
      * </p>
      * @return host url present as part of the http request object
     public String getHostURL()
          if (request == null)
               return null;//No request object present, hence return null
          String str = request.getServerName();
          //Log.debug("--- The request URL is --- " + str);
          return str;
      * Flushes <code>out</code> stream.
     public void flush()
          throws IOException
          if (pctx != null)
               pctx.getOut().flush();
}

Binding a JavaFX variable to a Java class instance variable

Hi,
I am pretty new to JavaFX but have been developing in Java for many years. I am trying to develop a JavaFX webservice client. What I am doing is creating a basic scene that displays the data values that I am polling with a Java class that extends Thread. The Java class is reading temperature and voltage from a remote server and storing the response in an instance variable. I would like to bind a JavaFx variable to the Java class instance variable so that I can display the values whenever they change.
var conn: WebserviceConnection; // Java class that extends Thread
var response: WebserviceResponse;
try {
conn = new WebserviceConnection("some_url");
conn.start();
Thread.sleep(10000);
} catch (e:Exception) {
e.printStackTrace();
def bindTemp = bind conn.getResponse().getTemperature();
def bindVolt = bind conn.getResponse().getVoltage();
The WebserviceConnection class is opening a socket connection and reading some data in a separate thread. A regular socket connection is used because the server is not using HTTP.
When I run the application, the bindTemp and bindVolt are not updated whenever new data values are received.
Am I missing something with how bind works? Can I do what I want to do with 'bind'. I basically want to run a separate thread to retrieve data and want my UI to be updated when the data changes.
Is there a better way to do this than the way I am trying to do it?
Thanks for any help in advance.
-Richard

Hi,
If you don't want to constantly poll for value change, you can use the observer design pattern, but you need to modify the classes that serve the values to javafx.
Heres a simple example:
The Thread which updates a value in every second:
// TimeServer.java
public class TimeServer extends Thread {
    private boolean interrupted = false;
    public ValueObject valueObject = new ValueObject();
    @Override
    public void run() {
        while (!interrupted) {
            try {
                valueObject.setValue(Long.toString(System.currentTimeMillis()));
                sleep(1000);
            } catch (InterruptedException ex) {
                interrupted = true;
}The ValueObject class which contains the values we want to bind in javafx:
// ValueObject.java
import java.util.Observable;
public class ValueObject extends Observable {
    private String value;
    public String getValue() {
        return this.value;
    public void setValue(String value) {
        this.value = value;
        fireNotify();
    private void fireNotify() {
        setChanged();
        notifyObservers();
}We also need an adapter class in JFX so we can use bind:
// ValueObjectAdapter.fx
import java.util.Observer;
import java.util.Observable;
public class ValueObjectAdapter extends Observer {
    public-read var value : String;
    public var valueObject : ValueObject
        on replace { valueObject.addObserver(this)}
    override function update(observable: Observable, arg: Object) {
         // We need to run every code in the JFX EDT
         // do not change if the update method can be called outside the Event Dispatch Thread!
         FX.deferAction(
             function(): Void {
                value = valueObject.getValue();
}And finally the main JFX code which displays the canging value:
// Main.fx
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.text.Text;
import javafx.scene.text.Font;
import threadbindfx.TimeServer;
var timeServer : TimeServer;
var valueObjectAdapter : ValueObjectAdapter = new ValueObjectAdapter();
timeServer = new TimeServer();
valueObjectAdapter.valueObject = timeServer.valueObject;
timeServer.start();
Stage {
    title: "Time Application"
    width: 250
    height: 80
    scene: Scene {
        content: Text {
            font : Font {
                size : 24
            x : 10, y : 30
            content: bind valueObjectAdapter.value;
}This approach uses less cpu time than constant polling, and changes aren't dependent on the polling interval.
However this cannot be applied to code which you cannot change obviously.
I hope this helps.

Instantiating an object of a class using variable

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