Expression evaluation

1
Expression evaluation

• E S C.
• S int.
• C Op ltarg1gt E ltarg2gt E.
• Op A M.
• A . M .

2
Class graph Find undefined things
Fig. UML1
Ident
definedThings
System

Thing

usedThings

def

S
Definition
T
body
Body
D
B
definedThings from System bypassing Body to
Thing usedThings from System through Body to
Thing
3
M1 Equation System
Fig. Eq1
EquationSystem
equations
Equation_List
Ident

Variable
lhs
Equation
Numerical
rhs
Expression_List
Simple
args
Expression

op
Add
Compound
4
CS1 UML class diagram Grammar
Fig. G1
Entry
0..
EParse
entries
Grammar
BParse
Production
rhs
Body
Part
parts
lhs
NonTerm
0..
Concrete
Abstract
5
YOUR PROJECTclass graph
6
Java Program Adaptive Method with DJ

• class System
• String id from Thing to edu.neu.ccs.demeter.I
  dent
• void repUndef(ClassGraph cg)
• checkDefined(cg, getDefThings(cg))
• HashSet getDefThings(ClassGraph cg)
• String definedThings
• "from System bypassing Body to Thing"
• Visitor v new Visitor()
• HashSet return_val new HashSet()
• void before(Thing v1)
• return_val.add(cg.fetch(v1, id) )
• public Object getReturnValue()return
  return_val
• cg.traverse(this, definedThings, v)
• return (HashSet)v.getReturnValue()

repUndef is a modular unit of crosscutting
implementation. Ad-hoc implementation may cut
across 100 classes.
green traversal black bold structure purple
advice red parameters
7
Java Program Adaptive Method with DJ

• void checkDefined(ClassGraph cg, final HashSet
  classHash)
• String usedThings
• from System through Body to Thing"
• cg.traverse(this, usedThings, new Visitor()
• void before(Thing v) Ident vn cg.fetch(v,
  vi)
• if (!classHash.contains(vn))
• System.out.println("The object "
  vn
• " is undefined.")
• )

8
Control Tangling and Scattering of Class
Structure, Traversals andTraversal Advice
9
Aspect-Oriented Programming

• Separating the following cross-cutting concerns
• Object Structure
• Traversals through Objects
• Advice on Traversals
• New behaviors based on collaborating objects
• Focus on those four concerns only. They appear
  frequently.

10
Why crosscutting?
overall graph object structure green graph
traversal purple advice
r0
BusList
Route1BusRoute
buses
busStops
BusStopList
Bus15DieselPowered
passengers
CentralSquareBusStop
waiting
PersonList
PersonList
JoanPerson
PaulPerson
SeemaPerson
EricPerson
r
r
11
Why aspects Oblivious

• Object Structure
• does not have to know about traversals and advice
  on traversals
• Traversals
• dont have to know about advice on traversals
• Advice on Traversals
• has to know minimally about object structure and
  traversals

12
Ad-hoc Implementationof three concerns

• Leads to lots of tangled code with numerous
  disadvantages
• The question is not how to eliminate the tangling
  but how to reduce it
• AOP is about tangling control the implementation
  of crosscutting concerns
• Crosscutting will always lead to some tangling at
  code level

13
Example

• Check whether all used entities are defined.
• Object structure, traversal (basically an
  introduction), advice on traversal

14
Find undefined things
definedThings
System

Thing

usedThings


Definition
Body
definedThings from System bypassing Body to
Thing usedThings from System through Body to
Thing
15
M1 Equation System
Fig. Eq1
EquationSystem
equations
Equation_List
Ident

Variable
lhs
Equation
Numerical
rhs
Expression_List
Simple
args
Expression

op
Add
Compound
16
Name map
Definition ClassDef Production
Equation
17
High-level description

• It is useful to have a high-level description of
  the collaboration besides the Java source code.
  Useful documentation.
• Ultimately we are interested in the executable
  form of the collaboration (Java source code).

18
Collaboration with strategies

• collaboration checkDef
• role System
• out repUndef()(uses getDefThings,
  checkDefined)
• getDefThings()(uses definedThings)
• checkDefined()(uses usedThings)
• in definedThings
• from System bypassing Body to Thing
• in usedThings
• from System through Body to Thing
• role Body
• role Thing
• role Definition

19
Collaboration with strategies

• collaboration COLLECT
• role System
• out HashSet collect()
• defined()(uses collect, definedThings)
• used()(uses collect, usedThings)
• in definedThings
• from System bypassing Body to Thing
• in usedThings
• from System through Body to Thing
• role Body
• role Thing
• role Definition

20
Use of collaboration Adapter

• Need to provide the expected methods (in methods)
  and provide name map.
• name map
• System EquationSystem
• Definition Equation
• Body Expression
• Thing Variable
• expected methods
• in definedThings // use default
• in usedThings // use default

21
What is an aspect?

• An aspect is a modular unit of crosscutting
  implementation.
• A Java method is a modular unit.
• Can we make a Java method an aspect?
• Yes, we call such methods adaptive methods.
• They cut across many classes in an ad-hoc
  implementation.

22
Java Program Adaptive Method

• class System
• String id from Thing to edu.neu.ccs.demeter.I
  dent
• void repUndef(ClassGraph cg)
• checkDefined(cg, getDefThings(cg))
• HashSet getDefThings(ClassGraph cg)
• String definedThings
• "from System bypassing Body to Thing"
• Visitor v new Visitor()
• HashSet return_val new HashSet()
• void before(Thing v1)
• return_val.add(cg.fetch(v1, id) )
• public Object getReturnValue()return
  return_val
• cg.traverse(this, definedThings, v)
• return (HashSet)v.getReturnValue()

green traversal black bold structure purple
advice red parameters
23
Java Program Adaptive Method

• void checkDefined(ClassGraph cg, final HashSet
  classHash)
• String usedThings
• from System through Body to Thing"
• cg.traverse(this, usedThings, new Visitor()
• void before(Thing v) Ident vn cg.fetch(v,
  id)
• if (!classHash.contains(vn))
• System.out.println("The object "
  vn
• " is undefined.")
• )

24
After applying name map

• For now we manually edit the Java program.

25
Java Program with less tangling

• class EquationSystem
• String id from Variable to
  edu.neu.ccs.demeter.Ident
• void repUndef(ClassGraph cg)
• checkDefined(cg, getDefThings(cg))
• HashSet getDefThings(ClassGraph cg)
• String definedThings
• "from EquationSystem bypassing
  Expression to Variable"
• Visitor v new Visitor()
• HashSet return_val new HashSet()
• void before(Variable v1)
• return_val.add(cg.fetch(v1, id) )
• public Object getReturnValue()return
  return_val
• cg.traverse(this, definedThings, v)
• return (HashSet)v.getReturnValue()

green traversal black bold structure purple
advice red parameters
26
Java Program with less tangling

• void checkDefined(ClassGraph cg, final HashSet
  classHash)
• String usedThings
• from EquationSystem through Expression
  to Variable"
• cg.traverse(this, usedThings, new Visitor()
• void before(Variable v) Ident vn
  cg.fetch(v, id)
• if (!classHash.contains(vn))
• System.out.println("The object "
  vn
• " is undefined.")
• )

27
Tangling is localizedScattering eliminated

• Instead of having code spread across several
  classes, it is localized in one class.
• Java program is describing the abstract pattern
  behind the computation of interest checking
  whether used entities are defined.
• Tangling control through abstraction of patterns.
  We abstract away from structure.

28
CS1 UML class diagram ClassG
definedThings from ClassG bypassing Body to
ClassName
Entry
0..
EParse
entries
ClassG
BParse
ClassDef
Body
Part
parts
className
0..
ClassName
Concrete
Abstract
29
CS1UML class diagram ClassG
usedThings from ClassG through Body to ClassName
Entry
0..
EParse
entries
ClassG
BParse
ClassDef
Body
Part
parts
className
0..
ClassName
Concrete
Abstract
30
M1 Equation System
Fig. Eq1
EquationSystem
equations
Equation_List
Ident

Variable
lhs
Equation
Numerical
rhs
Expression_List
Simple
args
Expression

op
Add
Compound
31
M1 Equation System
definedThings from EquationSystem bypassing
Expression to Variable
Fig. Eq2
EquationSystem
equations
Equation_List
Ident

lhs
Equation
Variable
Numerical
rhs
Simple
args
Expression_List
Expression
S
T

op
Add
Compound
D
B
32
M1 Equation System
usedThings from EquationSystem through
Expression to Variable
Fig. Eq3
EquationSystem
equations
Equation_List
Ident

lhs
Equation
Variable
Numerical
rhs
Simple
args
Expression_List
Expression
S
T

op
Add
Compound
D
B
33
Equation System Object
Fig. Eq4
equations
esEquationSystem
elsEquation_List
i1Ident
lhs
e1Equation
v1Variable
rhs
i2Ident
v2Variable
34
M1 Equation System
usedThings from EquationSystem through
Expression to Variable
Example x 1.0 . y ( x 4.0). z ( x y).
EquationSystem ltequationsgt List(Equation). Equat
ion ltlhsgt Variable ltrhsgt Expression
.. Variable Ident. Expression Simple
Compound. Simple Variable Numerical. Compound
( Op ltargsgt List(Expression) ). Op Add
Mul. Add . Mul . Numerical float.
35
M1 Equation System
definedThings from EquationSystem bypassing
Expression to Variable
Example x 1.0 . y ( x 4.0). z ( x y).
EquationSystem ltequationsgt List(Equation). Equat
ion ltlhsgt Variable ltrhsgt Expression
.. Variable Ident. Expression Simple
Compound. Simple Variable Numerical. Compound
( Op ltargsgt List(Expression) ). Op Add
Mul. Add . Mul . Numerical float.
36
CS1 UML class diagram Grammar
Fig. G1
Entry
0..
EParse
entries
Grammar
BParse
Production
rhs
Body
Part
parts
lhs
NonTerm
0..
Concrete
Abstract
37
CS1 UML class diagram Grammar
Fig. G2
definedThings from Grammar bypassing Body to
NonTerm
Entry
0..
EParse
entries
Grammar
BParse
Production
rhs
Body
Part
parts
lhs
NonTerm
0..
S
T
Concrete
Abstract
D
B
38
CS1UML class diagram Grammar
usedThings from Grammar through Body to NonTerm
Fig. G3
Entry
0..
EParse
entries
Grammar
BParse
Production
Body
rhs
Part
parts
lhs
NonTerm
0..
S
T
Concrete
Abstract
D
B
39
What DJ adds to AspectJ

• Point cut definitions based on connectivity in
  class graph.
• Define point cuts by specifying a (traversal)
  program based on class graph.
• Point cut reduction (high-level point cut
  designator) free programmer from details of
  class graph.
  
  
  
  
  
  

40
Context Switch

• Textbook and project
• Chapter 7 Before The Project
• Chapter 6 While You are Coding