Each of the files or classes of a projects source code represents a tree (AST). Looking at dependencies to other classes besides inheritance creates a graph though. Field types and method parameters are also implicit dependencies. Storing this information in a graph database like Neo4j allows for interesting queries and insights. Class-Graph provides that and is available as open-source github project.

1. Neo4j in Action
Software Metrics
Michael Hunger (@mesirii)
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2. Graphs in Software Technolgoy
๏ UML Diagrams are graphs
๏ dependencies between classes, packages, modules etc are graphs
๏ Software Metrics use dependency analysis
๏ Visualizations
๏ Cyclomatic Complexity,
๏ Fan-in (afferent-coupling) / Fan-out (efferent coupling) etc.
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3. Code City
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4. Class Diagram is a Graph
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5. SonarJ
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6. But there is more
๏Visualize & query Method, Field
dependencies
๏Collaborative filtering (co-usage)
๏Ranking
๏God classes
๏Paths between classes
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7. Welcome to Class-Graph
๏take a JAR
๏put it under ASM
๏scan it superfast
๏pull everything into Neo4j
๏add categories, indexes
๏Have Fun
http://github.com/jexp/class-graph 7
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8. Welcome to Class-Graph
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9. Interactive Hands-On Session
๏Lots of tasks
๏use Cypher to solve them
http://neo4j.org/resources/cypher
๏be creative, work together
๏ask !
๏Server http://bit.ly/innoq-neo4j
๏just the beginning
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10. Task: Find java.lang.Number and return it
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11. Task: Find java.lang.Number and return it
START o=node:types(name="java.lang.Number")
RETURN o;
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12. Task: Subclasses of Number?
•Return just the name
•Order them alphabetically
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13. Task: Subclasses of Number?
START n=node:types(name="java.lang.Number")
MATCH n<-[:SUPER_TYPE]-s
RETURN s.name
ORDER BY s.name;
•Return just the name
•Order them alphabetically
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14. Task: Which Methods does it have / how many
•Find the top 5 classes with the most members
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15. Task: Which Methods does it have / how many
START n=node:types(name="java.lang.Number")
MATCH n-[:METHOD_OF|FIELD_OF]->m
RETURN m;
•Find the top 5 classes with the most members
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16. Task: Calculate the fan-out of
java.lang.StringBuilder
•Calculate fan-in
•Which class has the highest fan-out
•What about package-level? 13
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17. Task: Calculate the fan-out of
java.lang.StringBuilder
START o=node:types(name="j.l.StringBuilder")
MATCH o-[:FIELD_OF]->f-[:FIELD_TYPE]->tf,
o-[:METHOD_OF]->m-[:PARAM_TYPE]->tp,
m-[:RETURN_TYPE]->tr
RETURN o,count(distinct tf)
+ count(distinct tp)
+ count(distinct tr) as fan_out;
•Calculate fan-in
•Which class has the highest fan-out
•What about package-level? 13
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18. Task: Find longest Inheritance Path
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19. Task: Find longest Inheritance Path
start c=node:types(name="java.lang.Object")
match path=p<-[:SUPER_TYPE*]-c
return extract(n in nodes(path) : n.name),
length(path) as len
order by len desc
limit 5;
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20. Task: Find the class that used IOException
most often
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21. Task: Find the class that used IOException
most often
START ex=node:types(name="java.io.IOException"
MATCH ex<-[:THROWS]-m<-[:METHOD_OF]-c
RETURN c, count(*)
ORDER BY count(*)
LIMIT 5;
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22. Task: Which other classes did classes that
threw IOException use most often?
•What could be a source of IOExceptions
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23. Task: Which other classes did classes that
threw IOException use most often?
START ex=node:types(name="java.io.IOException")
MATCH ex<-[:THROWS]-m<-[:METHOD_OF]-c,
mbr<-[:METHOD_OF|FIELD_OF]-c,
mbr-[:FIELD_TYPE|PARAM_TYPE|
RETURN_TYPE|THROWS]->other_type
WHERE other_type.name =~ /.+[.].+/
RETURN other_type.name, count(*)
ORDER BY count(*) desc
LIMIT 10;
•What could be a source of IOExceptions
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24. Task: Find a class you like and add a field with
your name and some type
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25. Task: Find a class you like and add a field with
your name and some type
START c=node:types(name="void"),
t=node:types(name="java.lang.reflect.Proxy")
CREATE c-[:FIELD_OF]->(field {name:“Michael“})
-[:FIELD_TYPE]->t;
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26. Task: Delete the most annoying class and all its
methods, fields and their relationships
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27. Task: Delete the most annoying class and all its
methods, fields and their relationships
START c=node:types(name="java.awt.List"),
MATCH c-[r1:FIELD_OF|METHOD_OF]->mbr-[r2]-()
c-[r]-()
DELETE c,mbr,r1,r2,r;
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