Auto Increment Serial No. in Java Project

Example : How to increase serial number automatically taking data from oracle 10g database.

import static javax.swing.JOptionPane.*;

public registration() 
{
   initComponents();        //Load event in Java
  
     void autoslno()
     {
       try
        {   
            Integer x=0; 
            Integer y=0;
            String q="select SLNO from BOOKDETAILS";
            pst=conn.prepareStatement(q);
            rs=pst.executeQuery();

            while (rs.next())
            {
              String cmbid=rs.getString("SLNO");
              cmbid.trim();
              x=Integer.parseInt(cmbid);
              if(y<x)
                {
                 y=x;
                }
                y=y+1;
                String cmbid1=Integer.toString(y);  //convert integer to string
                jTextFieldSLNO.setText(cmbid1);
             }                               
             System.out.print(x);
          }
        catch(Exception e)
        {
          JOptionPane.showMessageDialog(null,e);
        }
    }
}

---------  OR  ----------
public registration() 
{
    initComponents();
           
        Integer x=0;
        Integer y=0;
        try
          {
            String sql = "select REGSLNO from REGISTRATION";
            pst = conn.prepareStatement(sql);
            rs=pst.executeQuery();
            while(rs.next())
              {
                x= Integer.parseInt(rs.getString("REGSLNO"));            
                //showMessageDialog(null,x);
                if(y<x)
                 {
                    y=x;
                 }
                y=y+1;

                jTxtRegSlno.setText(Integer.toString(y));
             }
         }
        catch(Exception e)
        {
            out.println(e);
        }
}