Java thread safety - multiple atomic operations?

I'm just a non-developer playing to be a developer, so my question may be extremely simple!

I'm just testing Java multi-threading stuff, this is not real code. I wonder how to make two member variables update at the same time in Java, in case we want them both in sync. As an example:

public class Testing{  private Map<String, Boolean> itemToStatus = new ConcurrentHashMap<>();  private Set<String> items = ConcurrentHashMap.newKeySet();  public static void main(String[] args)  {    (new Testing()).start("ABC");  }  public void start(String name) {    if (name.equals("ABC")) {      itemToStatus.put(name, true);      items.add(name);    }  }}

In that scenario (imagine multi-threaded, of course) I want to be able to guarantee that any reads of items and itemToStatus always return the same.

So, if the code is in the line itemToStatus.put(name, true), and other thread asks items.contains(name), it will return false. On the other hand, if that other thread asks itemToStatus.containsKey(name); it will return true. And I don't want that, I want them both to give the same value, if that makes sense?

How can I make those two changes atomic? Would this work?

if (name.equals("ABC")) {    synchronised(this) {        itemToStatus.put(name, true);        items.add(name);    }}

Still, I don't see why that would work. I think that's the case where you need a lock or something?

Cheers!