Collections.synchronizedList is

Collections.synchronizedList is a fake and confused method

see the doc says:

  /**
     * Returns a synchronized (thread-safe) list backed by the specified
     * list.  In order to guarantee serial access, it is critical that
     * <strong>all</strong> access to the backing list is accomplished
     * through the returned list.<p>
     *
     * It is imperative that the user manually synchronize on the returned
     * list when iterating over it:
     * <pre>
     *  List list = Collections.synchronizedList(new ArrayList());
     *      ...
     *  synchronized (list) {
     *      Iterator i = list.iterator(); // Must be in synchronized block
     *      while (i.hasNext())
     *          foo(i.next());
     *  }
     * </pre>
     * Failure to follow this advice may result in non-deterministic behavior.
     *
     * <p>The returned list will be serializable if the specified list is
     * serializable.
     *
     * @param  <T> the class of the objects in the list
     * @param  list the list to be "wrapped" in a synchronized list.
     * @return a synchronized view of the specified list.
     */
    public static <T> List<T> synchronizedList(List<T> list) {
        return (list instanceof RandomAccess ?
                new SynchronizedRandomAccessList<>(list) :
                new SynchronizedList<>(list));
    }