But, yes, why’s it not on List, as I tend to use the interface rather than the implementation for my references.

Also, why does LinkedHashSet not implement List too?

Dealing with concurrency issues is more complicated than just adding a synchronized modifier to a method or using a synchronized block. Only a good design and well defined concurrency path will make an multithreading application well behaved.

if (!list.isEmpty()) object = list.get(0);

So you need to guard any set multiple accesses to make them atomic. It is fairly trivial to create a ReadWriteList implementation that transparently handles a ReadWriteLock for you, then you can guard your writes transparently:

interface ReadWriteList extends ArrayList, ReadWriteLock {}

ReadWriteList list = new ReadWriteListWrapper(new ArrayList());

list.readLock().lock();
if (!list.isEmpty()) object = list.get(0);
list.readLock().unlock();

You need to maintain your own lock/unlock blocks though, and you can’t transparently lock down your iterators unfortunately.