java.lang.NullP ointerException

[oll3i]

Exception in thread "AWT-EventQueue-0" java.lang.NullP ointerException
at Zad21.Cennik.ge tCenna(Cennik.j ava)
at Zad21.Kwiaciarn iaView$1.action Performed(Kwiac iarniaView.java )
at javax.swing.Abs tractButton.fir eActionPerforme d(Unknown Source)
at javax.swing.Abs tractButton$Han dler.actionPerf ormed(Unknown Source)

package Zad21;
 
import java.util.HashMap;
import java.util.Map;
 
public class Cennik {
     private static Cennik instance = null;
     Map<String,Double> cennik = new HashMap<String,Double> ();
 
       private Cennik() {  // prywatny konstruktor
       }
 
       public static Cennik getInstance() {
          if(instance == null) {
             instance = new Cennik();
 
          }
          return instance;
       }
 
public void setCennik(String nazwaKwiat,double cena){       
    cennik.put(nazwaKwiat,cena);   
}
 
public  Map<String,Double> getCennik(){ return cennik;}
 
public double getCenna(String nazwaKwiata){ return cennik.get(nazwaKwiata);}
}
 
 

in some other class

m_add.addActionListener( new ActionListener() {
    public void actionPerformed(ActionEvent e) {
         Cennik c= Cennik.getInstance();
 
 
         int a=Integer.parseInt(m_amount.getText());
         table.addRow((String)kwiatyList.getSelectedItem(),a,c.getCenna((String)kwiatyList.getSelectedItem()));
    }
  });
 

i want to get the value of selected item in combobox when a button is clicked
String)kwiatyLi st.getSelectedI tem(), and when a user enters some input into JTextField then take the both values when a button is clicked and add the entries to a table
i get the nullpointerexce ption in c.getCenna((Str ing)kwiatyList. getSelectedItem ()));

thank u

[oll3i]

i solved it thank u