SEKE 2012 Proceedings - Knowledge Systems Institute

To validate the proposed approach, we conduct an experimental
study on a popular open source software JHotDraw. We
compare the result with that reported by some other researches,
and find that our identification of Adapter pattern instances is
more precise, and identification result of State and Strategy
pattern instances is m uch more precise than that of existing
researches. For identification of Observer pattern instances, our
approach has relatively high precision. Our approach can identify
instances that cannot be i dentified by other methods, and
report more detailed information of the pattern instances, but it
cannot identify Observer instances that hasn't data dependence
relations between Subject and Observer.
The rest of this paper is organized as follows: Section II introduces
the implementation of dependence analysis in our tool
JDP-Detector; Section III and IV introduce approaches to identifying
adapting method and Notify method of observer pattern
respectively; Section V compares results of our experimentation
with that of other researches; Section VI concludes the
paper.
II. DEPENDENCE ANALYSIS AND ITS IMPLEMENTATION
We use two kinds of dependence relations in our approach:
control dependence and data dependence. Control dependence
relations are computed using the approach in [15]. Data dependence
relations are computed directly from define-use relations
[3]. The dependence relations is expressed by program
dependence graph (PDG). The Inter-procedural dependence is
expressed by system dependence graph (SDG), an extension of
PDG [14].
Construction of SDG is base d on information of method
call. We use points-to analysis to determine the callee of polymorphic
method call. As a pattern normally involves only several
classes, we adapt Soot and implement a local points-to
analysis that can start from entry of any method [4].
We develop a to ol named JDP-Detector based on Soot to
identify pattern instances in Java system. JDP-Detector
takes .class files as input, and transforms them into Jimple intermediate
representation [4]. Analysis is made on the Jimple
codes. JDP-Detector firstly identify pattern instance candidates
using structure information, and then make dependence analysis
on these candidates to get more precise result.
III.
IDENTIFICATION OF ADAPTING METHOD
A. Dependency Characteristics of Adapting Method
In Adapter pattern, class Adapter inherits from Target.
Method of Adaptee has fulfilled the function required by Target,
but has not the required interface, so the only work the
adapting method of Adapter needs to do is to call the method of
Adaptee and adapt the Adptee's interface to that of the Target.
So, strictly speaking, an adapting method m 1 consists of
three parts: (1) a call to method m 2 ; (2) statements (if available)
before the call, whose only duty is to prepare parameters for m 2 ;
(3) statements (if available) after the call, whose only duty is to
transform the output of m 2 to output of m 1 .
Based on the observation, we identify the adapting method
according to the following conditions: (1) m 1 calls m 2 ; (2) the
call statement depends on all the statements (when available)
before the call and part or all of m 1 's parameters; (3) the output
of m 1 depends on the call statement and all the statements
(when available) after the call; (4) the input and output of m 2
forms cut-set of m 1 's data dependence graph. Condition 4
means that the dataflow paths cannot bypass the call statement.
B. Case Study
Fig. 1 illustrates the structure of an Adapter instance identified
by JDP-Detector in JHotDraw 5.1. In the instance,
startConnector is the Adapter interface and connectorAt is the
Adaptee interface. Fig. 2 shows the PDG of startConnector, in
which the yellow node represents a call to connectorAt, the
green nodes represent the parameters of startConnector and the
statements before the call to connectorAt, the red node represents
the output of startConnector. As what can be seen from
Fig. 2, the PDG of startConnector matches the dependence
relation characteristic of adapting method.
Figure 1. An Object Adapter Instance in JHotDraw 5.1
Figure 2. The Dependence Graph of startConnector
IV.
IDENTIFICATION OF NOTIFY METHOD
A. Dependence Relation of Notify Method
The intent of Observer pattern is to "define a one-to-many
dependency between objects so that when one object changes
state, all its dependents are notified and updated automatically"
[1] . When Subject changes its state, its Notify method invokes
Update methods of all the Observers.
In some cases, the Subject only informs the Observers that
an event happens. As a classical implementation, the Subject
creates an event object, and sends it to Observer as a parameter
of Update. In some other cases, the Observer needs to update
values of its own fields to keep consistent with that of the Subject.
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