about variable persistence...

[Pradeep Adibatla]

I have a class and I have a variable...

The value of the variable is obtained from the DB.

Now I want to use this value across other java classes.

I have get and set for the variable.As soon as I receive the value from DB, I am setting it in it's set method so that I can call this in other classes...

What should be done in the class that wants to use the same value?

1)create an object of that class
2)if you say object.getVar() ---- it would be null...

should the variable be static? How do achieve it? somebody clarify this concept for me. thanks...

[Albareto McKenzie]

If the value of the variable is null can be because

the value retrieved from database is null

you are not setting the value correctly

you are executing first the access to the variable (object.getVar()) and then you are setting the value in that value

Which is your flow?

I don't know if your variable should be static (that depends on how do you want the variable to work) static means that it will be shared by every instance of the class, so imagine you have different users accessing the application, if the first one changes the value of that static then the second one will see the value that the first user has left, this behavour is useful but you have to see if it's what you want. Look at this: http://java.sun.com/docs/books/tutorial/java/javaOO/classvars.html

[Pradeep Adibatla]

I have a class;ClassA

ClassA
{
   private int idVal;
}

get,set for idVal;

The value of idVal is obtained from DB and is set in the set method...

say that the value returned from DB is 3.

Now I want to use this value whenever I require in other classes...what should be done?

say I have Classes B,C,D

ClassB
{
  public ClassA ca=new ClassA()
  
  void fun()
 {
   int a=ca.getIDVal()  (I want a to store 3 here...)
  }

}

similarly if C,D...

ClassC
{
  public ClassA ca=new ClassA()
  
  void fun()
 {
   int a=ca.getIDVal()  (I want a to store 3 here...)
  }

}

ClassD
{
  public ClassA ca=new ClassA()
  
  void fun()
 {
   int a=ca.getIDVal()  (I want a to store 3 here...)
  }

}

static retains the same copy of the variable across other classes but that's not helping...what could be the changes?

[Albareto McKenzie]

You have to think what you are doing here:

public ClassA ca=new ClassA();

you create a new ClassA but that element probably is empty, so you have no values inside, am I wrong?

[Pradeep Adibatla]

No,You are right! and I am unable to rectify it and get the value...

what should be done there?

[Albareto McKenzie]

Yes you are able, of course you are!

Think what do you want. You get the data from database (and that is a step that as far as I know you have already done) and then you have to set it in the ClassA object that you have created.

[Albareto McKenzie]

Sorry, my answer was not very elaborated, the steps are this:

data = getDataFromDatabase()
createClassAObject()
fillTheClassAObject(data)

[sujith Acharya]

to get the value set in the object of type ClassA, in the classes ClassB, ClassC, ClassD, you should have the reference of that object(ClassA) where the value is set , instaed of creating new objects in every class.

[Pradeep Adibatla]

@ sujith...

you mean to say just declare

public ClassA ca ;

in classes B,C,D??

but the reference would be null isn't it? 'ca' doesn't have any meaning in B,C,D...

It would be very clear in coding terms...

I would put that in coding terms...


@McKenzie ,hope this is what you meant!

Public ClassA
{
   public  ClassA ca;
   public int idVal;
 
   classA()
   {
       ca=new ClassA();
   }

  ssay idVal is 3.

   ...   get,set idVal

}

Now say ClassB is accessing it...


So ClassB would look like...

ClassB
{
   ///  what should go here??  
     1) a new object would be null
     2) refernce would be null

}

Still not clear!

[sujith Acharya]

  
Class ClassB {
 private ClassA ca;

//some arrangement like this has to be made, so that ClassB will have the handle to the object(of ClassA) where you have set the value from db. 

public setCa(ClassA objCa){
  this.ca = objCa;  
}

void fun() {  
 int a=ca.getIDVal(); 
}  


}

[Albareto McKenzie]

No, I was thinking more in something like:

Class DBUtils
{

private ResultSet getData()
{
   //do the query and whatever is needed to get the data from the db
   return data;
}

private ClassA getClassAFromData(ResultSet rs)
{
   ClassA myClass = new ClassA(); //empty object
    while(rs.next())
    {
        //fill your object here!
        myClass.setValue(rs.getWhateverYouHave());
        //more setters and blablabla
    }
}

public ClassA getClass()
{
    ResultSet myData = getData();
    return getClassAFromData(myData);
}

}

Class ClassB()
{
    public void myMethod()
    {
        DBUtils = new DBUtils();
        ClassA = DBUtils.getClassA();
    }
}

And you can implement whatever logic you want...

[Pradeep Adibatla]

Guys sorry for the delay but I still couldn't solve it!

This is the exact thing....


The two classes are DBToVocabularyObjectPersistence and RulesModelAction...

This the crux of what I was discussing... I have two Arraylists conceptAL and attributeAL as you can observe below in DBToVocabularyObjectPersistence class.. I want the two Arraylists with the populated data in RulesModelAction

  

public class DBToVocabularyObjectPersistence
{

	
    public static String vocabproID;

    public boolean boolDB=false;

    private RulesModelAction rma;
    

    public static ArrayList<String> conceptAL =new ArrayList<String>();
	public static ArrayList<String> attributeAL =new ArrayList<String>();
	public ArrayList<String> datatypeAL =new ArrayList<String>();
    public ArrayList<String> vocIDAL=new ArrayList<String>();


	public DBToVocabularyObjectPersistence()
	{
        System.out.println("In DBToVocabularyObjectPersistence ");
        rma=new RulesModelAction();
        rma.setDBToVocabularyObjectPersistence(this);
       		
	}

    public DBToVocabularyObjectPersistence(RulesModelAction rma)
	{
        System.out.println("In DBToVocabularyObjectPersistence LPA !!! ");
        this.rma=rma;

	}


    public boolean isBoolDB() {
        return boolDB;
    }

    public void setBoolDB(boolean boolDB) {
        this.boolDB = boolDB;
    }


    public String getVocabproID()
    {
        return vocabproID;
    }

    public void setVocabproID(String vocabproID)
    {

        System.out.println("The value passed is ---> "+vocabproID);

        DBToVocabularyObjectPersistence.vocabproID = vocabproID;

        System.out.println("The values is :--> "+ DBToVocabularyObjectPersistence.vocabproID);

       
    }

    private static final String mySQLDriverName = ServerPathProperties.getProperty("sampledb.dbdriver");
    private static final String connectionString = ServerPathProperties.getProperty("sampledb.dbURL");
    private static final String userName = ServerPathProperties.getProperty("sampledb.user");
    private static final String password = ServerPathProperties.getProperty("sampledb.password");

   public void getVocabGroupBy()
    {

        System.out.println("It's in getVocabGroupBy !!! ");

        System.out.println("VocabGroupBy id is  "+DBToVocabularyObjectPersistence.vocabproID);
        HashSet hSet=new HashSet();

     
        
        Connection conn = null;
		ResultSet rs1 = null;
		Statement stmt = null;
		ResultSetMetaData rsmd = null;
		String query="select * from vocabulary_table where PId="+DBToVocabularyObjectPersistence.vocabproID;
        
		try
		{

              //		Class c = Class.forName("com.mysql.jdbc.Driver");
              //		conn = DriverManager.getConnection("jdbc:mysql://blrkec121893d.ad.infosys.com/sampledb", "sbiuser", "sbiuser");

 			System.out.println("Enters connection");

            System.out.println(" The driver name is :-->"+mySQLDriverName);
            //Register the driver
            Class.forName(mySQLDriverName);

            conn = DriverManager.getConnection(connectionString, userName, password);

            System.out.println("conn is :-->"+conn);

            
			stmt = conn.createStatement();

            System.out.println("The stmt is :--> "+stmt);

		    rs1 = stmt.executeQuery(query);

            System.out.println("The rs1 is :--> "+rs1);

//		    int columns = 0;
//	        rsmd = rs1.getMetaData();
//	        columns = rsmd.getColumnCount();
//	        System.out.println("count is :-->" + columns);

		    int i=0;

		    while (rs1.next())
		    {
                System.out.println("The val  i is :--> "+i);

		    	String vid=rs1.getString("vocabularyid");
		    	String conceptName=rs1.getString("concept");
		    	String attributeName=rs1.getString("attribute");
		    	String datatype=rs1.getString("datatype");
		    	String pid=rs1.getString("PId");

                        vocIDAL.add(vid);
		    	conceptAL.add(conceptName);
		    	attributeAL.add(attributeName);
		    	datatypeAL.add(datatype);

                System.out.println("The ALSize is :--> "+conceptAL.size());
                

                for (Iterator it = conceptAL.iterator(); it.hasNext();)
                {
                    Object ob = it.next();
                    
                    System.out.println("Tghe set is :--> "+ob);

                }
            
             System.out.println("The set is :--> "+hSet.toString());

		     i++;

		    }

           

            boolDB=true;

        }
        catch (Exception e)
        {
            System.err.println("Got an exception! ");
            System.err.println(e.getMessage());
        }
    }



  

and this is what I am doing in RulesModelAction...

  

public class RulesModelAction extends ActionSupport 
{
    private String caPopup;
    private String ruleBack;
    
    private DBToVocabularyObjectPersistence dbtvop;

    public DBToVocabularyObjectPersistence getDBToVocabularyObjectPersistence()
    {
        return dbtvop;
    }

    public void setDBToVocabularyObjectPersistence(DBToVocabularyObjectPersistence dbtvop)
    {

//        dBToVocabularyObjectPersistence=new DBToVocabularyObjectPersistence();
//
//        System.out.println("dBToVocabularyObjectPersistence before is :--> "+dBToVocabularyObjectPersistence);

        this.dbtvop=dbtvop;

        System.out.println("dbtvop now is :--> "+dbtvop);
    }


    private ArrayList conceptARL;
    private ArrayList attributeARL;

String target;

    
    @Override
    public String execute() throws Exception 
    {
        System.out.println("\t\t----> In rules action class   ------------->  ");

       if (caPopup != null)
        {
            System.out.println("calPop is notNull");


           if (caPopup.equalsIgnoreCase("CreateConditionActionPopUpPanel"))
           {
               System.out.println("It matches create condition/action and its true");  
      //         System.out.print("The vocab is :--> "+vocabulary);

                try
                {

                  System.out.println(" In try !!!");


                   System.out.println("The dbtvop is :---> "+this.dbtvop);    //it's null here

                   System.out.println("The con size is :---> "+this.dbtvop.getConceptAL());

                    conceptARL=dbtvop.getConceptAL();
                    attributeARL=dbtvop.getAttributeAL();


                     System.out.println("caPopup in else !!!");

                     for (Iterator it = conceptARL.iterator(); it.hasNext();)
                     {
                        Object ob = it.next();

                         System.out.println("Tghe set is :--> "+ob);

                     }

           //       }

                  System.out.println("The conceptARL size is :--> "+conceptARL);
    
                  target= "success";

                }
                catch(Exception e)
                {
                    System.out.println(" ---> e is : "+e.getMessage());
                }
                
            }
        }

  

I want those two ArrayList values from DBToVocabularyObjectPersistence and to set them in this class...

[Albareto McKenzie]

First of all what is the flow of your program? Who calls who and so on? I cannot understand

Why is this static?

public static String vocabproID;

This:

 public void setVocabproID(String vocabproID)  
     {  
   
         System.out.println("The value passed is ---> "+vocabproID);  
   
         DBToVocabularyObjectPersistence.vocabproID = vocabproID;  
   
         System.out.println("The values is :--> "+ DBToVocabularyObjectPersistence.vocabproID);  
   
          
     }  

Is not correct, use this.vocabproID = vocabproID; (assuming vocabproID is not static of course)

Why ar you doing this:

vocIDAL.add(vid);  
conceptAL.add(conceptName);  
attributeAL.add(attributeName);  
datatypeAL.add(datatype);  

You have four ArrayList, why don't you create an Object with that four elements as attributes and you fill the object, once it's filled you can add it to an ArrayList<myObject>


How do you get the values to the RulesModelAction class?
do you really want this: public void getVocabGroupBy() ?

[Campbell Ritchie]

Please note your code is difficult to read if you don't use th Code button.

[Pradeep Adibatla]

First of all what is the flow of your program? Who calls who and so on? I cannot understand

Actually in the flow, I am in class RulesModelAction...

Now I need to get the ArrayLists into this class...

I know these arraylists can be obtained can be obtained from DB...So I am calling this class DBToVocabularyObjectPersistence to fill the ArrayLists and use them in RulesModelAction...

Why is this static?

public static String vocabproID;

This:

# public void setVocabproID(String vocabproID)
# {
#
# System.out.println("The value passed is ---> "+vocabproID);
#
# DBToVocabularyObjectPersistence.vocabproID = vocabproID;
#
# System.out.println("The values is :--> "+ DBToVocabularyObjectPersistence.vocabproID);
#
#
# }

Is not correct, use this.vocabproID = vocabproID; (assuming vocabproID is not static of course)

This is unused code,removed!!!

How do you get the values to the RulesModelAction class?
do you really want this: public void getVocabGroupBy() ?

That is what my problem,how to get values in RulesModelAction

That method is fetching values from DB!

[Albareto McKenzie]

Hey Cambpbell, you are right, I changed it, I was sooooo lazy :P

Pradeep please provide more information about the flow. You only say that you are in the flow but we don't know where are you coming from and which method is calling what.

I would recommend you to do something like this:

Create an object that will contain the info from the DB

    
public class MyObject
{
    private String vid;
    private String conceptName;
    private String attributeName;
    private String datatype;

    //Create getters and setters for this elements
}

then in would your getVocabGroupBy() to something like this:

 public ArrayList<MyObject> getVocabGroupBy()
{
    ArrayList<MyObject> queryResult = new ArrayList<MyObject>();
    // variables you need to launch the query
    rs1 = stmt.executeQuery(query);  
       
    while(rs1.next())
    {
         MyObject obj = new MyObject();
         obj.setVid(rs1.getString("vocabularyid"));
         //the other setters
        //once you have your Object filled you set it to the ArrayList
        queryResult.add(obj);
    }
    //close connection and everything and the last line of the method:
   return queryResult;
}    

Then when you need the information from the database CALL this method and store the result in the ArrayList, then you iterate over it and use the information that contains:

//somewhere you need the information from DB
ArrayList<MyObject> infoFromDB = getVocabGroupBy();

for(MyObject object: infoFromDB)
{
    //do whatever with your object using the getters
}

Do you understand what I mean?