Question

I have a class Cache which picks up List<SomeObject> someObjectList from DB and stores it in static variable.

Now I have another thread A which uses this List as follows

class A extends Thread{
  private List<SomeObject> somobjLst;

  public A(){
    somobjLst = Cache.getSomeObjectList();
  }

 void run(){
  //somobjLst used  in a loop here, no additong are done it , but its value is used
 }
}

1. Now if at some point of time if some objects are added to Cache.someObjectList will it reflect in class A. I think it should as A only holds a refrence to it.
2. Will there will be any problem in A’s code when content of Cache.someObjectList change?

EDIT:
As per suggestions :
if i make

  void run (){
  while(true){
     synchronized(someObjList){


    }
     try{
     Thread.sleep(INTERVAL);
     }catch(Exception e){
     }
  }
 }

will this solve problem?

Answer 1

1. Yes, the changes will be reflected in class A as well. Exactly as you say: A holds a reference to the exact same object as Cache.

2. Yes, it can lead to a problem if A doesn’t expect it to change. It also can lead to a problem if the List implementation is not thread safe (most general-purpose implementations are not thread-safe!). Accessing a non-thread-safe data structure from two threads at the same time can lead to very nasty problems.