Java interface Problem

I've got an interface:

package com.aex;

import javax.jws.WebParam;

public interface IFonds {
    double getKoers();
    String getNaam();
    void setKoers(@WebParam(name="koers") double koers); }

And the class:

    /*
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 * and open the template in the editor.
 */

package com.aex;

import java.io.Serializable;
import javax.jws.*;

/**
 *
 * @author Julian
 */
@WebService
public class Fonds implements IFonds, Serializable {

    String naam;
    double koers;

    public double getKoers() {
        return koers;
    }

    public String getNaam() {
        return naam;
    }

public Fonds()
{
}

    public Fonds(String naam,  double koers)
    {
        this.naam = naam;
        this.koers = koers;

    }

    public void setKoers(@WebParam(name="koers")double koers) {
        this.koers = koers;
    }

}

Now I want to send over an collection of the interface with a webservice, so here is my class I send:

package com.aex;

import java.util.Collection;
import java.util.*;
import javax.jws.*;

/**
 *
 * @author Julian
 */
@WebService
public class AEX implements IAEX {

    Collection&开发者_运维问答lt;IFonds> fondsen;

    public Collection<IFonds> getFondsen() {
        return fondsen;
    }


    public AEX()
    {
        IFonds fonds1 = new Fonds("hema", 3.33);


        //fondsen.add(fonds1);
    }

    public double getKoers(@WebParam(name="fondsnaam")String fondsNaam){

        Iterator iterator = fondsen.iterator();

        while(iterator.hasNext())
        {
            Fonds tempFonds = (Fonds)iterator.next();
            if(tempFonds.getNaam().endsWith(fondsNaam))
            {
                return tempFonds.getKoers();
            }

        }
        return -1;
    }

}

The problem is that I get an nullpointerexception in the constructor of the last shown class (AEX). This is because I want to add the object into the interface collection. Anyone got solution for this?

---

Yes: initialize your collection variable!

public AEX()
{
    IFonds fonds1 = new Fonds("hema", 3.33);

    // This is the line you were missing
    fondsen = new ArrayList<IFonds>();
    fondsen.add(fonds1);
}

Note that this actually has nothing to do with interfaces or web services... reference type fields default to null unless you explicitly initialize them, whatever the context.