@SuppressWarnings("unchecked")
    public KTableKTableJoinMerger<K, VR> joinMerger() {
        final ProcessorSupplier<K, Change<VR>, K, Change<VR>> kChangeProcessorSupplier = (ProcessorSupplier<K, Change<VR>, K, Change<VR>>) mergeProcessorParameters().processorSupplier();
        return (KTableKTableJoinMerger<K, VR>) kChangeProcessorSupplier;
    }
The supplier which provides processor with KTable-KTable join merge functionality.
streams/src/main/java/org/apache/kafka/streams/kstream/internals/graph/KTableKTableJoinNode.java