question: public static < U , W > AtomicReferenceFieldUpdater < U , W > newAtomicReferenceFieldUpdater ( Class < U > tClass , Class < W > vClass , String fieldName ) { try { return new UnsafeAtomicReferenceFieldUpdater < > ( JUnsafe . getUnsafe ( ) , tClass , fieldName ) ; } catch ( Throwable t ) { return AtomicReferenceFieldUpdater . newUpdater ( tClass , vClass , fieldName ) ; } }
target:  Creates and returns an updater for objects with the given field.