@Deprecated
    @Override
    public void init(final ProcessorContext context, final StateStore root) {

        // register the store
        context.register(root, (key, value) -> {
            restoring = true;
            put(Bytes.wrap(key), value);
            restoring = false;
        });
    }
An in-memory LRU cache store based on HashSet and HashMap.
streams/src/main/java/org/apache/kafka/streams/state/internals/MemoryLRUCache.java