need help with school project

[Dudu Yohanshvilli]

Hello, I got homework to make a worker list, I have to make it with 3 files:
1-MYSQL connection
2-WorkerLoad - loads from the database
3-WorkersInfo - prints the database info
I succeded to the first 2 but having troubles with the third, help please??
the first file is:

package connection;

import java.sql.*;
import java.util.Collection;
import java.util.LinkedList;

public class MYSQLconnection{
    private static ThreadLocal<Connection> con = new LocalConnection();
    
    public static Connection getConnection() {
        return con.get();
    }
    
    public static void closeAll() throws SQLException {
        for (Connection con : LocalConnection.allConnections) {
            con.close();
        }
    }
    public static class LocalConnection extends ThreadLocal<Connection> {
        public static Collection<Connection> allConnections = new LinkedList<Connection>();

        @Override
        protected Connection initialValue() {
            String driver = "com.mysql.jdbc.Driver";
            String url = "jdbc:mysql://localhost:3306/";
            String userName = "root";
            String password = "ROOT";
            String dbName = "schoolproject";
            try {
                Class.forName(driver).newInstance();
                Connection conn = DriverManager.getConnection(url+dbName,userName,password);
                System.out.println("Connected to the database");
                allConnections.add(conn);
                return conn;
            } catch (Exception e) {
                e.printStackTrace();
                return null;
            }
        }
    }
}

the second:

package Loads;

import connection.MYSQLconnection;
import Infos.WorkersInfo;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.LinkedList;
import java.util.List;

//id name

public class WorkerLoad {
    private int id;
    private String name;
    private List<WorkersInfos> work = new LinkedList<WorkersInfos>();
    private static WorkerLoad instance = new WorkerLoad();
    
    public void loadFromDb(int workerid) throws SQLException {
        WorkerLoad ret = new WorkerLoad();
        Connection con = MYSQLconnection.getConnection();
        PreparedStatement ps = con.prepareStatement("SELECT * FROM workers WHERE id=?");
        ps.setInt(1, workerid);
        ResultSet rs = ps.executeQuery();
        /*if (!rs.next()) {
            rs.close();
            ps.close();
            System.out.println("something failed"); 
        }*/
        while(rs.next()){
            System.out.println("dfsgdsfgdfsgdfs");
            ret.id = rs.getInt("id");
            ret.name = rs.getString("name");
            System.out.println("worker number "+ret.id);
            final WorkersInfos rank = new WorkersInfos(rs.getInt("id"),rs.getString("name"));
            work.add(rank);

            
        }
        rs.close();
        ps.close();
    }
  
    
    public static void main(String[] args) throws SQLException {
        WorkerLoad abc = new WorkerLoad();
        abc.loadFromDb(1);
        abc.loadFromDb(2);
        WorkersInfo vvv = new WorkersInfo();
        vvv.check();
        

    }
  
    public static WorkerLoad getInstance() {
        return instance;
    }
        public List<WorkersInfos> getWork() {
        return work;
    }
        public static class WorkersInfos {

        private String namez;
        private int idz;

        public WorkersInfos(int idz, String namez) {
            this.idz = idz;
            this.namez = namez;
        }

        public String getName() {
            return namez;
        }

        public int getId() {
            return idz;
        }
    }
        
        
        
}

the third:

package Infos;



import Loads.WorkerLoad;
import Loads.WorkerLoad.WorkersInfos;
import java.util.Arrays;
import java.util.List;

public class WorkersInfo {
    public void check(){
        StringBuilder ret = new StringBuilder();
        String s = null;
        final List<WorkersInfos> work = WorkerLoad.getInstance().getWork();
        for (WorkersInfos info : work) {
            ret.append("name = ");
            ret.append(info.getName());
            ret.append("id = ");
            ret.append(info.getId());
        }
            s=ret.toString();
            System.out.println(s);         

    }
}

I don't know why, but in the third, the FOR don't work


(sorry for the bad english)

[Campbell Ritchie]

Welcome to the Ranch

What do you mean by not working? We need to know more details.
I suggest you precede that for loop by a line like this

System.out.printf("The work List contains %d elements.%n", work.size());

[Dudu Yohanshvilli]

Campbell Ritchie wrote:Welcome to the Ranch

What do you mean by not working? We need to know more details.
I suggest you precede that for loop by a line like this

System.out.printf("The work List contains %d elements.%n", work.size());

First- Thank You!!!,
I used your suggestion, and I don't know why but it says that I have 0 elements, when I need to have 2, but there is what I need:
I have in MySql a table called "workers"
it contains ID and Name
lets say I have 2 workers,
id: 1, name: Dudu
id: 2, name: James

I want it to connect to the database, collect the information of the workers (id+name)
and then print it, all this need to be done with 3 different pages
1 for the connection to the MYSQL
1 for loading
and the last 1 for printing

something is wrong, I think with the loading, but can't figure out what is wrong!!

P.S:
I found the problem, when I do getInstance().getWork(); I don't know why but it returns 0 instead of 2 when I print the work.size();
I think it don't save the work list, any suggestions??

I can't find how to fix it=[

[Praveen Kumar M K]

In WorkerLoad, I dont see a call being made to the method loadFromDb.

[Dudu Yohanshvilli]

Praveen Kumar M K wrote:In WorkerLoad, I dont see a call being made to the method loadFromDb.

    public static void main(String[] args) throws SQLException {  
        WorkerLoad abc = new WorkerLoad();  
        abc.loadFromDb(1);  
        abc.loadFromDb(2);  
        WorkersInfo vvv = new WorkersInfo();  
        vvv.check();  
          
  
    }

[Praveen Kumar M K]

Oh so your running class is WorkerLoad!(When you said that the second class succeeded, it put me off track)

instance is a static variable, but the very first line of main creates a new WorkerLoad object. So where are you connecting that to instance

[Dudu Yohanshvilli]

Praveen Kumar M K wrote:Oh so your running class is WorkerLoad!(When you said that the second class succeeded, it put me off track)

instance is a static variable, but the very first line of main creates a new WorkerLoad object. So where are you connecting that to instance

in WorkersInfo.java:

public class WorkerInfo {
    public void check(){
        StringBuilder ret = new StringBuilder();
        String s = null;
        final List<WorkersInfos> work = WorkerLoad.getInstance().getWork();
        for (WorkersInfos info: work) {
            ret.append("name = ");
            ret.append(info.getName());
            ret.append("id = ");
            ret.append(info.getId());
            
        }
            s=ret.toString();
            System.out.println(s);         

    }
}

when I put the line:

System.out.printf("The work List contains %d elements.%n", work.size());  

under

System.out.println(s); 

it returns 0, when actully it need to return 2,

but when I put the same line in WorkerLoad.java inside the loadFromDB under

ret.name = rs.getString("name");

first it return 1, then 2 (thats ok because I call the function twice, and it has to be 2)


so the problem is somewhere in WorkerInfo with the get instnace,

p.s:
there is "WorkersInfo" and "WorkerInfos" don't get confused =]

[Praveen Kumar M K]

Again, this is you main function

public static void main(String[] args) throws SQLException {   
        WorkerLoad abc = new WorkerLoad();   
        abc.loadFromDb(1);   
        abc.loadFromDb(2);   
        WorkersInfo vvv = new WorkersInfo();   
        vvv.check();     
    }

And this is the call in check method

final List<WorkersInfos> work = WorkerLoad.getInstance().getWork();  

Here you are fetching the static instance variable and calling the getWork method on it. Has this static instance variable been assigned to anything?

abc.getWork() is not equal to WorkerLoad.getInstance().getWork();

[Dudu Yohanshvilli]

wow!! thank you very much!!! I am sitting on this error for more then 3 hours!! I think even more then 5 hours, thank you very much!! it works now=]
and again, thank you!!

[Praveen Kumar M K]

Welcome! Do share here the change that you did, so that other ranchers can benefit.

[Dudu Yohanshvilli]

Praveen Kumar M K wrote:Welcome! Do share here the change that you did, so that other ranchers can benefit.

The changes something little:
in WorkerLoad change the main to:

    public static void main(String[] args) throws SQLException {
        WorkerInfo vvv = new WorkerInfo();
        vvv.check();
    }

and in WorkerInfo
in the check() class
delete the work variable and add to the begginging:

        WorkerLoad abc = new WorkerLoad();
        abc.loadFromDb(1);
        abc.loadFromDb(2);
        final List<InfoList> work = abc.getWork();

and everything else is the same!

[Praveen Kumar M K]

Sure, but wouldnt it be easier to make just this change in your main function

public static void main(String[] args) throws SQLException {      
        WorkerLoad abc = WorkerLoad.getInstance(); //<-- right here    
        abc.loadFromDb(1);      
        abc.loadFromDb(2);      
        WorkersInfo vvv = new WorkersInfo();      
        vvv.check();        
    } 

The idea here with the static instance is to work with only ONE instance of WorkerLoad object, else it would be of no use.