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Creating a new object from a list choice

Posted on 2006-11-07
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Medium Priority
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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
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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
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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 2000 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
 
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

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