@Override
    public String toString() {
        return "KTableKTableJoinNode{" +
            "joinThisStoreNames=" + Arrays.toString(joinThisStoreNames()) +
            ", joinOtherStoreNames=" + Arrays.toString(joinOtherStoreNames()) +
            "} " + super.toString();
    }
The supplier which provides processor with KTable-KTable join merge functionality.
streams/src/main/java/org/apache/kafka/streams/kstream/internals/graph/KTableKTableJoinNode.java