@Override
        @Nullable
        public V setValue(@Nullable V value) {
            V previous = this.value;
            this.value = value;
            return previous;
        }
A single map entry.

@param <K> the key type
@param <V> the value type
ttl-core/src/main/java/com/alibaba/ttl3/internal/util/ConcurrentReferenceHashMap.java