Besides concurrent collections, we also have synchronized collections. Java provides a suite of wrappers that expose a collection as a thread-safe collection. These wrappers are available in Collections. The most common ones are as follows:

• synchronizedCollection​(Collection<T> c): Returns a synchronized (thread-safe) collection backed by the specified collection
• synchronizedList​(List<T> list): Returns a synchronized (thread-safe) list backed by the specified list:

List<Integer> syncList 
  = Collections.synchronizedList(new ArrayList<>());

• synchronizedMap​(Map<K,​V> m): Returns a synchronized (thread-safe) map backed by the specified map:

Map<Integer, Integer> syncMap 
  = Collections.synchronizedMap(new HashMap<>());

• synchronizedSet​(Set<T> s): Returns a synchronized (thread-safe) set backed by the specified set:

Set<Integer> syncSet 
  = Collections.synchronizedSet(new HashSet<>());