Nija Shi

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Reverse Engineering of Design Patterns in Java
Source Code
Ron Olsson olsson_at_cs.ucdavis.edu

• Nija Shi
• shini_at_cs.ucdavis.edu

Department of Computer Science University of
California, Davis
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Outline

• Introduction
• Current Approaches
• A Motivating Example
• Reclassification of the GoF patterns
• Our Initial Prototype PINOT
• Results
• Future Work

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Design Patterns

• What are they?
• A design pattern offers guidelines on when, how,
  and why an implementation can be created to solve
  a general problem in a particular context.
• What are they not?
• Reusable libraries, a framework

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The Singleton Pattern

• Intent Ensure a class has only one instance and
  provide a global
• point of access to it.
• Example

• public class Singleton
• private static Singleton INSTANCE null
• private Singleton()
• public static Singleton getInstance()
• if (INSTANCE null)
• INSTANCE new Singleton()
• return INSTANCE

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Design Patterns

• The Gang of Four (GoF) Patterns
• Based on use, design patterns are categorized
  into
• Creational Patterns
• Focus on how objects get created
• Structural Patterns
• Focus on the ways to decouple classes by role
• Behavioral Patterns
• Focus on separating object responsibilities based
  on polymorphism and delegation

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Design Pattern Examples
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Reverse Engineering

• Why Reverse Engineering?
• Legacy code
• Program understanding
• Source code upgrade/migration
• Insufficient documentation
• Current program understanding tools
• Debugging tools
• Program analysis tools
• CSCOPE, SourceNavigator, SourceInsight, etc.
• Improve current program understanding tools
• Bring program understanding to the design level

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Reverse Engineering Design Patterns
Singleton
Composite
layoutMgr 1
AbstractFactory
1
Strategy
Bridge
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Representative Current Approaches
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Current Approaches

• Can be grouped as the following
• Targeting structural aspects
• Targeting behavioral aspects

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Targeting Structural Aspects

• Method
• Extract structural relationships (inter-class
  analysis)
• For a pattern, check for certain structural
  properties
• Drawback
• Relies only on structural relationships, which
  are not the only distinction between patterns

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Targeting Behavioral Aspects

• Method
• Narrow down search space
• using inter-class relationships
• Verify behavior in method bodies
• Dynamic analysis
• Machine learning
• Static program analysis

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Targeting Behavioral Aspects

• Drawback
• Dynamic analysis
• Requires good data coverage
• Verifies program behavior but does not verify the
  intent
• Complicates the task for detecting patterns that
  involve concurrency
• Machine learning
• Most patterns have concrete definitions, thus
  does not solve the fundamental problem.

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A Motivating Example
public class Singleton private static
Singleton instance private Singleton()
public static Singleton getInstance()

• Detecting the
• Singleton Pattern
• As detected by FUJABA
• Common search criteria
• private Singleton()
• private static Singleton instance
• public static Singleton getInstance()
• Problem
• No behavioral analysis on getInstance()
• Solution?

if (instance NULL) instance new
Singleton() return instance
instance new Singleton() return instance
return new Singleton()

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GoF Patterns Reclassified
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Language-provided Patterns

• Patterns provided in the language or library
• The Iterator Pattern
• Provides a way to access the elements of an
  aggregate object sequentially without exposing
  its underlying representation
• In Java
• Enumeration since Java 1.0
• Iterator since Java.1.2
• The for-each loop since Java 1.5
• The Prototype Pattern
• Specify the kinds of objects to create using a
  prototypical instance, and create new objects
  based on this prototype
• In Java
• The clone() method in java.lang.Object
• Pattern Detection
• Recognizing variants in legacy code

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Structure-driven Patterns

• Patterns that are driven by software
  architecture.
• Can be identified by inter-class relationships
• The Template Method, Composite, Decorator,
  Bridge, Adapter, Proxy, Facade Patterns
• Inter-class Relationships
• Accessibility
• Declaration
• Inheritance
• Delegation
• Aggregation
• Method invocation

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Behavior-driven Patterns

• Patterns that are driven by system behavior.
• Can be detected using inter-class and program
  analyses.
• The Singleton, Abstract Factory, Factory Method,
  Flyweight, CoR, Visitor, Observer, Mediator,
  Strategy, and State patterns.
• Program analysis techniques
• Program slicing
• Data-flow analysis
• Call trace analysis

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Domain-specific Patterns

• Patterns applied in a domain-specific context
• The Interpreter Pattern
• Given a language, define a representation for
  its grammar along with an interpreter that uses
  the representation to interpret sentences in the
  language
• Commonly based on the Composite and Visitor
  patterns
• The Command Pattern
• Encapsulate a request as an object, thereby
  letting you parameterize clients with different
  requests, queue or log requests, and support
  undoable operations
• A use of combining the Bridge and Composite
  patterns to separate user interface and actual
  command execution. The Memento pattern is also
  used to store a history of executed commands
• Pattern Detection
• Requires domain-specific knowledge

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Generic Concepts

• Patterns that are generic concepts
• The Builder Pattern
• Separate the construction of a complex object
  from its representation so that the same
  construction can create different representation
• System bootstrapping pattern, object creation is
  not necessary
• The Memento Pattern
• Without violating encapsulation, capture and
  externalize an objects internal state so that
  the object can be restored to this state later
• Implementation of memo pool and representation of
  states are not specifically defined.
• Pattern detection
• Lack implementation trace

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Recognizing the Singleton Pattern

• Structural aspect
• private Singleton()
• private static Singleton instance
• public static Singleton getInstance()
• Behavioral aspect
• Analyze the behavior in getInstance()
• Check if lazy-instantiation is used
• Check if instance is returned
• Slice the method body for instance and analyze
  the sliced program

recall
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Recognizing the Singleton Pattern
public class SingleSpoon private
SingleSpoon() private static SingleSpoon
theSpoon public static SingleSpoon
getTheSpoon() if (theSpoon null)
theSpoon new SingleSpoon() return
theSpoon
control-flow graph
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Pattern INference and recOvery Tool

• PINOT
• A fully automated pattern detection tool
• Designed to be faster and more accurate
• How PINOT works

Pattern Instances
Source Code
Text
Pattern Instances
view
XMI
editors
U
M
L
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Implementation Alternatives

• Program analysis tools
• Extract basic information of the source code
• Class, method, and variable declarations
• Class inheritance
• Method invocations, call trace
• Variable refers-to and refers-by relationships
• Parsers
• Extract the abstract syntax tree (AST)
• Compilers
• Extract the AST and provide related symbol tables
  and built-in functions operating on the AST

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Pattern INference and recOvery Tool

• Implementation Overview
• A modification of Jikes (open source C Java
  compiler)
• Analysis using Jikes abstract syntax tree (AST)
  and symbol tables
• Identifying Structure-driven patterns
• Considers Java language constructs
• Considers commonly used Java utility classes
  java.util.Collection and java.util.Iterator
• Identifying Behavior-driven patterns
• Applies data-flow analysis, inter-procedural
  analysis, alias analysis
• PINOT considers related patterns
• Speed up the process of pattern recognition
• E.g., Strategy and State Patterns, CoR and
  Decorator, etc.

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Yes. The tool provides recognition for the
pattern and correctly identifies it.
No. The tool provides recognition for the
pattern but fails to identify it.
Blank. The tool does not provide recognition for
the pattern.
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Benchmarks

• Java AWT (GUI toolkit)
• javac (Sun Java Compiler)
• JHotDraw (GUI framework)
• Apache Ant (Build tool)
• Swing (Java Swing library)
• ArgoUML (UML editor tool)

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More Results
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Future Work

• Investigate other domain-specific patterns
• High performance computing (HPC) patterns
• Real-time patterns
• Security patterns
• Extend usability of PINOT
• Formalize pattern definitions
• Visualizing detection results

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PINOT Eclipse
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Conclusion

• Reverse engineering design patterns
• Reclassifying the GoF patterns for
  reverse-engineering
• About PINOT
• Future work