Load Some Information From Previous Object Files And Add New Objects To Them Afterwards

I have a project in java that asks me to load some information from previous object files and add new objects to them afterwards. I created the files, but when I close the program and search for the previous information that should've been saved in the object file , it return nothing.

Here is the code.

Add method:

public boolean addUser (User u){
users[Ucount]=u;
Ucount++;
return true;
}

The save method:

public void saveUser (){
try{
FileOutputStream FOS = new FileOutputStream("User.txt", true);
ObjectOutputStream OOS = new ObjectOutputStream (FOS);

[Code] ....

The read method:

public void readUser (){
try{
FileInputStream FIS = new FileInputStream ("User.txt");
ObjectInputStream OIS = new ObjectInputStream (FIS);
for (int i=0;i<Ucount;i++){

[Code] ....

*Note: When I open the object file I could see that the information are actually there, so I think there's a problem with the read method I'm not sure what it is.