java - how to add an arraylist of objects to file -

i want write program have sign , sign in button. if user press sign button username , password must written file. have problem in appending file. have arraylist of object(user) called people, , add arraylist file. when print contents of file see first user, , if print arraylist, has 1 object last one. here addmethod in class:

public class addtofile  {     arraylist<user> people = new arraylist<user>();     user user;      public void add(string username, string password) throws filenotfoundexception, ioexception, classnotfoundexception      {         user u1 = new user(username, password, "hello", null, null, null);          fileoutputstream fout = new fileoutputstream("f.txt", true);         objectoutputstream out = new objectoutputstream(fout);         people.add(u1);         system.out.println(people.size());         (user people1 : people)          {             system.out.println("user  " + people1.username + "  pass " + people1.password);         }         (user p : people)          {             out.writeobject(p);                }         out.flush();         out.close();          system.out.println("success");          objectinputstream = new objectinputstream(new fileinputstream("f.txt"));         user u = (user) is.readobject();         system.out.println("file  user :" + u.username + "    pass:" + u.password);         is.close();            }     } 

that user class implements serializable.

you can have multiple files each objects (user) , keep in directory different file names. using directory file name reader method, can read files names in directory. read each files , convert user objects. don't think append object stream work.

        arraylist<user> people = new arraylist<user>();     user user;      user u1 = new user(username, password, "hello", null, null, null);      people.add(u1);     system.out.println(people.size());     (user people1 : people) {         system.out.println("user  " + people1.username + "  pass "                 + people1.password);     }     (user p : people) {         fileoutputstream fout = new fileoutputstream("/tempobjects/"                 + p.getusername(), true); // assume user name unique         objectoutputstream out = new objectoutputstream(fout);         out.writeobject(p);         out.flush();         out.close();     }      system.out.println("success");      file folder = new file("/tempobjects/"); //reading folder     file[] listoffiles = folder.listfiles(); // file names in folder      (int = 0; < listoffiles.length; i++) { // reading each file details         if (listoffiles[i].isfile()) {             objectinputstream = new objectinputstream(new fileinputstream(listoffiles[i].getname()));             user u = (user) is.readobject();             system.out.println("file  user :" + u.username + "    pass:"    + u.password);             is.close();         }     }