android - Sending ArrayList<Object> through socket. Java -

what i'm trying send , arraylist through socket android client java server. here code of client sends arraylist :

private void sendcontacts(){             apphelper helperclass = new apphelper(getapplicationcontext());             final arraylist<person> list = helperclass.getcontacts();             system.out.println("lenght of contacts array : " +list.size()); //          (person person : list) { //              system.out.println("name "+person.getname()+"\nnumber "+ person.getnr()); //          }              handler.post(new runnable() {                  @override                 public void run() {                     // todo auto-generated method stub                     try { //**151 line**              os.writeobject(list);                      os.flush();                 } catch (ioexception e) {                     // todo auto-generated catch block                     log.e(tag, "sending contact list has failed");                     e.printstacktrace();                 }             }             }); }  public arraylist<person> getcontacts() {         arraylist<person> alcontacts = null;         contentresolver cr = mcontext.getcontentresolver(); //activity/application android.content.context         cursor cursor = cr.query(contactscontract.contacts.content_uri, null, null, null, null);         if(cursor.movetofirst())         {              alcontacts = new arraylist<person>();                         {                 string id = cursor.getstring(cursor.getcolumnindex(contactscontract.contacts._id));                  if(integer.parseint(cursor.getstring(cursor.getcolumnindex(contactscontract.contacts.has_phone_number))) > 0)                 {                     cursor pcur = cr.query(contactscontract.commondatakinds.phone.content_uri,null,contactscontract.commondatakinds.phone.contact_id +" = ?",new string[]{ id }, null);                     while (pcur.movetonext())                      {                         string contactnumber = pcur.getstring(pcur.getcolumnindex(contactscontract.commondatakinds.phone.number));                         string contactname = pcur.getstring(pcur.getcolumnindex(contactscontract.commondatakinds.phone.display_name));                         person temp = new person(contactname, contactnumber);                          alcontacts.add(temp);                         break;                     }                     pcur.close();                 }              } while (cursor.movetonext()) ;         }         return alcontacts;     } 

here server code:

private void whilechatting() throws ioexception {         abletotype(true);         string message = "you connected ";         sendmessage(message);         {// have conversation             try {                 message = (string) input.readobject();                 // message = (string) input.readline();                 showmessage("\n" + message);             } catch (classnotfoundexception e) {                 showmessage("it not string\n");                  // todo: handle exception             }             try{                 arraylist<person> list =(arraylist<person>) input.readobject();                 showmessage("got list of person size :" + list.size());             }catch(classnotfoundexception e){                 showmessage("it not list of person\n");             }         } while (!message.equals("client - end"));     } 

error code :

caused by: java.io.notserializableexception: com.lauris.client.person     @ java.io.objectoutputstream.writenewobject(objectoutputstream.java:1344)     @ java.io.objectoutputstream.writeobjectinternal(objectoutputstream.java:1651)     @ java.io.objectoutputstream.writeobject(objectoutputstream.java:1497)     @ java.io.objectoutputstream.writeobject(objectoutputstream.java:1461)     @ java.util.arraylist.writeobject(arraylist.java:648)     @ java.lang.reflect.method.invoke(native method)     @ java.lang.reflect.method.invoke(method.java:372)     @ java.io.objectoutputstream.writehierarchy(objectoutputstream.java:1033)     @ java.io.objectoutputstream.writenewobject(objectoutputstream.java:1384)     @ java.io.objectoutputstream.writeobjectinternal(objectoutputstream.java:1651)     @ java.io.objectoutputstream.writeobject(objectoutputstream.java:1497)     @ java.io.objectoutputstream.writeobject(objectoutputstream.java:1461)     **at com.lauris.client.mainactivity$clientthread$4.run(mainactivity.java:151)**     @ android.os.handler.handlecallback(handler.java:739)     @ android.os.handler.dispatchmessage(handler.java:95)     @ android.os.looper.loop(looper.java:135)     @ android.app.activitythread.main(activitythread.java:5221)     @ java.lang.reflect.method.invoke(native method)     @ java.lang.reflect.method.invoke(method.java:372)     @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:899)     @ com.android.internal.os.zygoteinit.main(zygoteinit.java:694) 

i guess problem serialization ? don't understand meaning of ? can explain me is, why need it? , how may fix code?

additional question. can see in code im trying listen different inputstreams. think i,m doing wrong. more advanced explain me how correct ?

appreciate help, i'm stuck on this.

the person class must implement serializable:

import java.io.serializable;  public class person implements serializable {      /**      *       */     private static final long serialversionuid = 1l;  }