Java: Serializing beginner problem :-(

package sotring;
import java.io.*;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.*;

import com.sun.org.apache.bcel.internal.generic.INEG;

public class storeing {

    public static void storeMail(Message[] mail){
        try {
        	ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("mail.ser"));
            out.writeObject(mail);
            out.flush();
            out.close();

        } catch (IOException e) {
        }
    }

    	public static Message[] getStoredMails(){

	 try
	 {

		ObjectInputStream in = new ObjectInputStream(new FileInputStream("mail.ser"));
		Message[] array = (Message[]) in.readObject() ;
	 	for (int i=0; i< array.length;i++)
	 		System.out.println("EMail von:"+ array[i].getSender() + " an " + array[i].getReceiver()+ " Emailbetreff: "+ array[i].getBetreff() + " Inhalt: " + array[i].getContent());

	 	System.out.println("Size: "+array.length);	//return array;
	 	in.close();
	 	return array;
	 }
	 catch(IOException ex)
	 {
	 	ex.printStackTrace();
	 	return null;
	 }
	 catch(ClassNotFoundException ex)
	 {
	 	ex.printStackTrace();
	 	return null;
	 }
}

    public static void main(String[] args) {
    	User user1 = new User("User1", "geheim");
    	User user2 = new User("User2", "geheim");

    	Message email1 = new Message(user1.getName(), user2.getName(), "Test", "Fooobaaaar");
    	Message email2 = new Message(user1.getName(), user2.getName(), "Test2", "Woohoo");
    	Message email3 = new Message(user1.getName(), user2.getName(), "Test3", "Okay =) ");
    	Message [] mails = {email1, email2, email3};
    	storeMail(mails);
    	Message[] restored = getStoredMails();;
    }
}

public class Message implements Serializable{

    static final long serialVersionUID = -1L;

    private String receiver;  //Empfänger
    private String sender;  //Absender
    private String Betreff;
    private String content;
    private String timestamp;

    private String getDateTime() {
        DateFormat dateFormat = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
        Date date = new Date();
        return dateFormat.format(date);
    }

    Message (String receiver, String sender, String Betreff, String content) {
    	this.Betreff= Betreff;
    	this.receiver = receiver;
    	this.sender = sender;
    	this.content = content;
    	this.timestamp = getDateTime();
    }

    Message() {  // Just for loaded msg
    }

    public String getReceiver() {
    	return receiver;
    }

    public void setReceiver(String receiver) {
    	this.receiver = receiver;
    }

    public String getSender() {
    	return sender;
    }

    public void setSender(String sender) {
    	this.sender = sender;
    }

    public String getBetreff() {
    	return Betreff;
    }

    public void setBetreff(String betreff) {
    	Betreff = betreff;
    }

    public String getContent() {
    	return content;
    }
    public String getTime() {
    	return timestamp;
    }
    public void setContent(String content) {
    	this.content = content;
    }

}

public class User implements Serializable{

    static final long serialVersionUID = -1L;
    private String username;  //unique Username
    private String ipadress;  //changes everytime
    private String password;  //Password
    private int unreadMsg;    //Unread Messages
    private static int usercount;
    private boolean online;

    public String getName(){
    	return username;
    }
    public boolean Status() {
    	return online;
    }

    public void setOnline() {
    	this.online = true;
    }
    public void setOffline() {
    	this.online = false;
    }

    User(String username,String password){
    	if (true){
    		this.username = username;
    		this.password = password;
    		usercount++;

    	} else System.out.print("Username not availiable");
    }

    public void changePassword(String newpassword){
    	password = newpassword;
    }

    public void setIP(String newip){
    	ipadress = newip;
    }

    public String getIP(){
    	if (ipadress.length() >= 7){
    		return ipadress;
    	} else return "ip address not set.";
    }



    public int getUnreadMsg() {
    	return unreadMsg;
    }
}

public static Message[] getStoredMails(){

     try
     {

            ObjectInputStream in = new ObjectInputStream(new FileInputStream("mail.ser"));
            Message[] array = (Message[]) in.readObject() ;
            System.out.println("Size: "+array.length);      //return array;
            in.close();
            return array;
     }
     catch(IOException ex)
     {
            ex.printStackTrace();
     }
     catch(ClassNotFoundException ex)
     {
            ex.printStackTrace();
     }
     return null; //fix
}

public static Message[] getStoredMails(){

         try
         {

                ObjectInputStream in = new ObjectInputStream(new FileInputStream("mail.ser"));
                Message[] array = (Message[]) in.readObject() ;
                System.out.println("Size: "+array.length);      //return array;
                in.close();
                return array;
         }
         catch(IOException ex)
         {
                ex.printStackTrace();
         }
         catch(ClassNotFoundException ex)
         {
                ex.printStackTrace();
         }

         return null;
    }