Solved

Creating a new object from a list choice

Posted on 2006-11-07
23
187 Views
Last Modified: 2010-03-31
Hi Experts


Here is my question :

From a list I get one or more selection that goes into a sortedList.
From that list I have to create a new object that correspond to the class name.

for example my first choice is SwingTrader and that choice correspond to the creation of a SwingTrader object...
 
Here is the code :


private class OKListener implements ActionListener {
          public void actionPerformed(ActionEvent e) {
          
                  
                  xxxxxxxx st = new xxxxxx(destListModel,pointer);
                  
                } else{
                
                }

What do I have to do to create that object automatically


Thank you
0
Comment
Question by:blarouche
  • 10
  • 8
  • 5
23 Comments
 
LVL 86

Expert Comment

by:CEHJ
ID: 17892113
You can map String to class

Map<String, Class> stringToClass = new HashMap<String, Class>();
stringToClass.put("StringTrader", a.b.c.StringTrader.class);


Object x = stringToClass.get("StringTrader").newInstance();
0
 

Author Comment

by:blarouche
ID: 17892182
I don't know how to figure that out

The next choice for example could be "swing"


When the user click on the OK button now I have to create an object from the swing class.

What would be my code in the actionPerformed button?




0
 
LVL 86

Expert Comment

by:CEHJ
ID: 17892431
>>What would be my code in the actionPerformed button?


Object x = stringToClass.get((String)list.getSelectedObject()).newInstance();
0
 

Author Comment

by:blarouche
ID: 17892599
CEHJ


there is something I don't understand because I have to include parameters in the creation of my object.

SwingTrader has to be replaced by the selection but I have to include destListModel and pointer parameters

SwingTrader st = new SwingTrader(destListModel,pointer);


0
 

Author Comment

by:blarouche
ID: 17892756
I don't want to have to write code like that :


if (system == "SwingTrader"){                            
            SwingTrader st = new SwingTrader(destListModel,pointer);
                } else{}          
                
if (system == "Swing"){                            
            Swing st = new Swing(destListModel,pointer);
                } else{}          

etc ............
0
 
LVL 92

Accepted Solution

by:
objects earned 500 total points
ID: 17892889
you can store the Class objects themselves in the list
then to

Class clazz = (Class) list.getSelectedValue();

> I have to include parameters in the creation of my object.

Are the parameters the same?
if so use something like:

Constructor ctor = clazz.getDeclaredConstructor(new Class[] { ListModel.class, Object.class}) ;
Object o = ctor.newInstance(new Object[] {estListModel, pointer});

If the parameters are different, then I'd suggest storing a factory in the list where the factory handles the object creation.
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 17892899
Make the SwingTrader a bean - give it an empty ctor and give it setListModel and setPointer methods
0
 
LVL 92

Expert Comment

by:objects
ID: 17892948
> Make the SwingTrader a bean - give it an empty ctor and give it setListModel and setPointer methods

unnecessary, they can be passed in the ctor as I've shown above
u could even store the Constructor in the list to save you some work.

You would use a custom list renderer to comtrol what is actually displayed in the list

0
 
LVL 86

Expert Comment

by:CEHJ
ID: 17893014
No need to use reflection. Most Java classes should be designed as beans anyway as they will increase their compatibility with other APIs thereby
0
 

Author Comment

by:blarouche
ID: 17893022
objects

here is my modified code

private class OKListener implements ActionListener {
          public void actionPerformed(ActionEvent e) {
                
                Class clazz = (Class) system;
                
                Constructor ctor = clazz.getDeclaredConstructor(new Class[] { ListModel.class, Object.class});
                Object o = ctor.newInstance(new Object[] {destListModel, pointer});
                
}


Now system is a String coming from a user selection.

I have the following error :
Cannot cast from String to Class
0
 
LVL 92

Expert Comment

by:objects
ID: 17893109
use the getSelectedValue() to get Object from list

eg.

Class clazz = (Class) list.getSelectedValue();
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 
LVL 86

Expert Comment

by:CEHJ
ID: 17893141
>>Now system is a String coming from a user selection.


Object x = stringToClass.get(system).newInstance();
0
 
LVL 92

Expert Comment

by:objects
ID: 17893214
If you don't want to store the Class objects in the list then use:

Class clazz = Class.forName(system);

Though more efficient to store Class (or Constructor's) in list
0
 

Author Comment

by:blarouche
ID: 17893344
I've got a number of unhandled exception

What would be my catch blocks

for example
catch(ClassNotFoundException ect){}
catch(NoSuchMethodException  et){}
0
 
LVL 92

Expert Comment

by:objects
ID: 17894777
> What would be my catch blocks

just:

catch (Exception ex) {

if you don't have specific actions to take for different exceptions
and if you do add exception blocks for the exceptions you want to handle seperately before it
0
 

Author Comment

by:blarouche
ID: 17898242
Sorry

I am coming back to you because I had to work on somethig else

It still doesn't work. When I run the code nothing happens. When I call the constructor for class SwingTrader I should be executing a method.

Here is my  code :

private class okbuttonListener implements ActionListener {

          public void actionPerformed( ActionEvent e )
          {
              LinkedList list = new LinkedList();  
              for(int i = 0; i < destList.getModel().getSize(); i++) {
              list.add(destList.getModel().getElementAt(i));                                  
                }
              
                selectedsystem = txt.getText();
                
                
                final LoadXMLConfiguration chemin;
          chemin = new LoadXMLConfiguration("C:/XML/chemin.xml",true);
          String Lechemin = chemin.getDriver();
                        
          try{
          Class clazz = Class.forName(selectedsystem);
          Constructor ctor = clazz.getDeclaredConstructor(new Class[] { String.class, String.class, LinkedList.class, Object.class});
           Object o = ctor.newInstance(new Object[]      {Lechemin+"src/SteadFast/systems/SwingTrader.xml","C:/XML/chemin.xml",list, pointer});
             }
              catch(Exception ex){}


           dispose();                
          }
       }



Do you see something from that code that is wrong ?
0
 
LVL 92

Expert Comment

by:objects
ID: 17902254
>               catch(Exception ex){}

change that so u know if something goes wrong

              catch(Exception ex) { ex.printStackTrace(); }

Make sure selectedsystem is the fully qualified class name (ie. also contains package).
0
 

Author Comment

by:blarouche
ID: 17902557
Here is the result when I include the package name :


java.lang.NoSuchMethodException: systems.SwingTrader.<init>(java.lang.String, java.lang.String, java.util.LinkedList, java.lang.Object)
      at java.lang.Class.getConstructor0(Unknown Source)
      at java.lang.Class.getDeclaredConstructor(Unknown Source)
      at GUI.SystemSelection$okbuttonListener.actionPerformed(SystemSelection.java:372)
      at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
      at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
      at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
      at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
      at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
      at java.awt.Component.processMouseEvent(Unknown Source)
      at javax.swing.JComponent.processMouseEvent(Unknown Source)
      at java.awt.Component.processEvent(Unknown Source)
      at java.awt.Container.processEvent(Unknown Source)
      at java.awt.Component.dispatchEventImpl(Unknown Source)
      at java.awt.Container.dispatchEventImpl(Unknown Source)
      at java.awt.Component.dispatchEvent(Unknown Source)
      at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
      at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
      at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
      at java.awt.Container.dispatchEventImpl(Unknown Source)
      at java.awt.Window.dispatchEventImpl(Unknown Source)
      at java.awt.Component.dispatchEvent(Unknown Source)
      at java.awt.EventQueue.dispatchEvent(Unknown Source)
      at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
      at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
      at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
      at java.awt.EventDispatchThread.run(Unknown Source)
0
 

Author Comment

by:blarouche
ID: 17903218
I am increasing the points because I am stuck with this problem.
0
 
LVL 92

Expert Comment

by:objects
ID: 17903847
thats saying the class does not have a ctor that takes those args, what ctors does SwingTrader have?
0
 

Author Comment

by:blarouche
ID: 17905666
When I run this code :

Constructor con[]= Class.forName("systems.SwingTrader").getDeclaredConstructor();
 for (int x=0;x<con.length;x++)
System.out.println("Constructor "+x+" = "+con[x]);
}
catch(Exception ex){ ex.printStackTrace();}

I get :

Constructor 0 = public systems.SwingTrader()
Constructor 1 = public systems.SwingTrader(java.lang.String,java.lang.String)
Constructor 2 = public systems.SwingTrader(java.lang.String,java.lang.String,java.util.LinkedList,quotes.DBQuotes)


I have three constructors in my SwingTrader class :
Here they are :

  /**
     * Constructor 1
     */
    public SwingTrader() {
        this.systemName         = "Break out of n days";
        this.systemDescription  = "Break Out system)";
        this.systemAuthor       = "Bernard Larouche";
        this.showInfo();
     
    }
      
    /**
     * Constructor 2
     * @param configFile
     */
    public SwingTrader(String configFile, String xmldirectory) {
        super(configFile,xmldirectory);
        // TODO Auto-generated constructor stub
    }
      
   
        /**
     * Constructor 3
     * @param configFile
     */
    public SwingTrader(String Config,String xmldir,LinkedList list, DBQuotes pointer) {
        super(Config,xmldir,list,pointer);
       
    }


and Here my three constructors from the super class ASystem :

    /**
     * Constructor
     */
    public ASystem(){};
   

   
    /**
     * Constructor
     * @param symbol
     */
    public ASystem(String configFile, String xmldirectory){
            way = new LoadXMLConfiguration("C:/XML/chemin.xml",true);
            String theway = way.getDriver();
        conf = new LoadXMLConfiguration(configFile,true);
        this.configurationFile = configFile;
        dir = new LoadXMLConfiguration(xmldirectory,true);
        this.directory = xmldirectory;
        // for each symbol in configuration file run this system
        for (int i=0;i<conf.getSymbols().length;i++){
            this.symbol = conf.getSymbols()[i];
            confcost = new LoadXMLConfiguration(theway+"jars/config/commissions/"+symbol+"Spec.xml",true);
            this.symbolminmove = confcost.getMinMove();
            executeSystem();
        }
       
    }

   
    public ASystem(String configFile,String xmldirectory,LinkedList list, DBQuotes pointer){
          
          
          this.LList = list;
          this.pointer = pointer;
          way = new LoadXMLConfiguration("C:/XML/chemin.xml",true);
            String theway = way.getDriver();
            conf = new LoadXMLConfiguration(configFile,true);
        this.configurationFile = configFile;
            dir = new LoadXMLConfiguration(xmldirectory,true);
        this.directory = xmldirectory;
            
        // for each symbol in configuration file run this system
        for (int i=0;i<LList.size();i++){
            this.symbol = (String)LList.get(i);
            confcost = new LoadXMLConfiguration(theway+"jars/config/commissions/"+symbol+"Spec.xml",true);
            this.symbolminmove = confcost.getMinMove();
            executeSystem();
        }
     
    }














0
 
LVL 92

Expert Comment

by:objects
ID: 17905673
>           Constructor ctor = clazz.getDeclaredConstructor(new Class[] { String.class, String.class, LinkedList.class, Object.class});

should be

          Constructor ctor = clazz.getDeclaredConstructor(new Class[] { String.class, String.class, LinkedList.class, DBQuotes.class});
0
 

Author Comment

by:blarouche
ID: 17905713
objects

You are the best !!


Thank you
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
allswap challenge 6 76
Unable to start eclipse ? 17 128
mockito example issue 8 62
JList custom Cell Renderer refresh 15 53
For beginner Java programmers or at least those new to the Eclipse IDE, the following tutorial will show some (four) ways in which you can import your Java projects to your Eclipse workbench. Introduction While learning Java can be done with…
Introduction This article is the first of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article explains our test automation goals. Then rationale is given for the tools we use to a…
Viewers will learn about basic arrays, how to declare them, and how to use them. Introduction and definition: Declare an array and cover the syntax of declaring them: Initialize every index in the created array: Example/Features of a basic arr…
The viewer will learn how to implement Singleton Design Pattern in Java.

914 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

20 Experts available now in Live!

Get 1:1 Help Now