Can object(instance TreeMap) be inserted in a File by objectoutputstream??

Question

Can a object containing TreeMap instance be inserted in a File by objectoutputstream??
class pfore{
static class TextFile
          String category;
          String filename;
                TreeMap filewords;
                TextFile( )
                {category=filename=null;
                 filewords=new TreeMap();
                TextFile(String category,String filename,TreeMap filewords)
          this.category=category;
          this.filename=filename;
               // this.filewords=new TreeMap();
                this.filewords=new TreeMap(filewords);
public static void main (String args[]){
//creating an object of TextFile by reading a text file and also initializing it
TextFile ob=new TextFile("dd","ff",kp);
//kp is a created TreeMap object
*__try{    FileOutputStream fos= new FileOutputStream("serrial.txt");__*
           *__ObjectOutputStream oos=new ObjectOutputStream(fos);__*
            *__oos.writeObject(ob);__*               
             *__oos.flush();__*
             *__oos.close();__*
                  *__catch(IOException e) {__*
       *__System.out.println("exception while opening the filestream"+e);__*
       *__e.printStackTrace();__*
       *__System.exit(0);__*
}//end main
}//end class
Please see the underlined part because other parts are completely ok.
it's giving exceptions like
at.java.io.objecstreamclass invokewriteObject
at.java.io.objectoutputstream.writeserialData
at.java.io.objectoutputstream.writeOrdinaryObject.etc..etc

Answer 1

suppose a class is a textfile in java..containing a TreeMap instance ,and two string variables as instance..
class textfile implements Serializable
String foo;
String foo1;
TreeMap t;
textfile t=new textfile( );now how to write object t in file??
with objectoutputstream i have tried it..bt it is throwing exceptions..
the details i have posted in my previous Question(see above-the code)
please give in details how to do this??