Exception in thread "main" java.lang.NullPointerException

[farooqhussain786]

I am new to java. And I am keeping receiving this error message. I don't know why this is happening

import java.util.*;
import javax.swing.*;
/**
 *
 * @author Administrator
 */
public class CarRegistation {
    private ArrayList CarOwner = null;
    private ArrayList CarRegInfo = null;

     public void CarRegistation(){
        CarOwner = new ArrayList();
        CarRegInfo = new ArrayList();
    }

     public void newCarRegistation(String oc, String nic, String man, String Reg){
         //try{
              //PersonsInfo p = new PersonsInfo(oc, nic);
              PersonsInfo p = new PersonsInfo(oc, nic);
              Cars c = new Cars(man, Reg);
              CarOwner.add(p);         //error comes here Null Pointer
              CarRegInfo.add(c);
         /*}catch (Exception e){
            JOptionPane.showMessageDialog(null, e.getMessage());
      }*/
    }

     public void searchCarRegistation (String n) {
        // try{
             for(int i=0; i<CarOwner.size(); i++){
                 PersonsInfo p = (PersonsInfo)CarOwner.get(i);
                 Cars c = (Cars)CarRegInfo.get(i);
                 if (n.equals(p.getName())){
//                     WindowsApplication wa = new WindowsApplication();
//                     wa.txtManufacturer.setText(c.getCarManufacturer());
//                     wa.txtOwnerOfCar.setText(p.getName());
//                     wa.txtNicNo.setText(p.getNicNo());
//                     wa.txtRegistationNo.setText(c.getRegistation());
                }
            }
        /*}catch (Exception e){
            JOptionPane.showConfirmDialog(null, e.getMessage());
      }*/
    }

     public void deleteCarRegistation(String nic){
         /*try{*/
             for(int i=0; i<CarOwner.size(); i++){
                 PersonsInfo p = (PersonsInfo)CarOwner.get(i);
                 //Cars c = (Cars)CarRegInfo.get(i);
                 if (nic.equals(p.getNicNo())){
                     CarOwner.remove(i);
                     CarRegInfo.remove(i);
                     JOptionPane.showMessageDialog(null, "Car having NIC: " + p.getNicNo() + "has been remove from list");
                 }
             }
         //}catch (Exception e){
           //  JOptionPane.showConfirmDialog(null, e.getMessage());
         //}
     }

     public int countCarRegistation(String n){
         int size = 0;
         //try{
             for(int i=0; i<CarOwner.size();i++){
                 PersonsInfo p = (PersonsInfo)CarOwner.get(i);
                 if(n.equals(p.getName())){
                     size = size + 1;
                 }
             }
         //}
         //catch (Exception e){
         //    JOptionPane.showConfirmDialog(null, e.getMessage());
        // }
         return size;
     }

}

Please help me out as I have to submit this code ASAP. Thanks in advance.

[k4ff1n34dd1c7]

I am guessing it has to do with your arraylists? is pointing into a null position. post you java error stack. Its had to tell without knowing where the error occurs

[farooqhussain786]

Exception in thread "main" java.lang.NullPointerException
at mytesting.CarRegistation.newCarRegistation(CarRegi station.java:29)
at mytesting.Main.main(Main.java:29)

I have four class right now. One of then is PersonalInfo and Cars these are classes which I want to make collection and main class

[mtyoung]

CarOwner is null
how can a null object call method size

i cant find constructor in your class

[farooqhussain786]

public void CarRegistation(){
CarOwner = new ArrayList();
CarRegInfo = new ArrayList();
}

this is the constructor

[xbox_nutter]

just ran a couple of quick tests and this seemed to work

When declaring your arrays try :

private ArrayList<PersonsInfo> CarOwner = new ArrayList<PersonsInfo>();

And i know it is sometimes easy to over look stuff when passing Variables so make sure the types in the constructor for Car and personInfo accept strings!!

[farooqhussain786]

Not Working anyone else help please please do it

[farooqhussain786]

thx for everyone i have resolve my problem 'mtyoung' is very close i have constructor but its not working for me

[mtyoung]

public void CarRegistation(){}
never be a constructor

above is a void method call CarRegistation

without self defined constructor, default constructor will initialize your ArrayList

[Nisha18]

myToung is right

[farooqhussain786]

thx myToung, Nisha and everyone else who help to solve my problem.