@Override
    public String toString() {
        return "StreamStreamJoinNode{" +
               "thisWindowedStreamProcessorParameters=" + thisWindowedStreamProcessorParameters +
               ", otherWindowedStreamProcessorParameters=" + otherWindowedStreamProcessorParameters +
               ", thisWindowStoreBuilder=" + thisWindowStoreBuilder +
               ", otherWindowStoreBuilder=" + otherWindowStoreBuilder +
               ", outerJoinWindowStoreBuilder=" + outerJoinWindowStoreBuilder +
               ", joined=" + joined +
               "} " + super.toString();
    }
Too much information to generalize, so Stream-Stream joins are represented by a specific node.
streams/src/main/java/org/apache/kafka/streams/kstream/internals/graph/StreamStreamJoinNode.java