Effective Java

by Joshua Bloch

The Apache SynchronizedCollection class is still being actively maintained, but as of this writing, it does not override the removeIf method. If this class is used in conjunction with Java 8, it will therefore inherit the default implementation of removeIf, which does not, indeed cannot, maintain the class’s fundamental promise: to automatically synchronize around each method invocation. The default implementation knows nothing about synchronization and has no access to the field that contains the locking object. If a client calls the removeIf method on a SynchronizedCollection instance in the presence of concurrent modification of the collection by another thread, a ConcurrentModificationException or other unspecified

Nice example