java - Is it possible to allow different thread both read to and write from the same collection? -

i have following wrapper:

public usercontianer{      private list<user> users;       public void add(user u){          users.add(u)     }      public void update(user u){         if(users.contains(u))              //updating new value u     }      public user get(int index){         return users.get(index);     } } 

i need allow multiple thread read , write container simultaneously such that

• if read , written element of list different- should ok

• if read , written element of list same then

  • if there's thread updating element read operation should blocked untill write operation's finished

  • if there's thread reading element, write operations should blocked until reading's finished

first of all, such requirements make sense? i'm new multithreading , maybe that's actualy not wanted.

secondly, possible implement requirements in java?

one option wrap existing list in synchronized version collections.synchronizedlist(list<t> list). allows thread-safe use of list, if access through synchronized wrapper.

note elements in list references. if want lock list while you're making changes objects, you'll need synchronize @ higher level. 1 way mark methods synchronized.

 public synchronized void update(user u) { ... }