Help with null pointer exception...

Hi,

I don't know why but i'm getting a null pointer exception when i call this method.

/**

* To String method

*/

public String toString()

{

String returnString;

returnString =" House ID : "+ id +"\n House address : " + address +"\n Date Built : " + df.format(dateBuilt) +"\n Selling price : " + nf.format(sellingPrice)

+"\n Sold : " + isSold +"\n";

if(soldDate!=null){

returnString +=" Date of sale : "+ df.format(soldDate);

}

return returnString;

}

My instance variables are as follows..

private String id;

private String address;

private double sellingPrice;

public boolean isSold;

private Date dateBuilt;

private Date soldDate;

private Buyer buyer;

private boolean yearDifference;

private DateFormat df;

private double stampDuty;

private NumberFormat nf;

Can anyone help me? Thanks

[1409 byte] By [Capsuda] at [2007-11-27 3:42:21]