Dealing with Generalization: Pull Up and Push Down Refactoring

Lecture 20 of SE602 Software Re-Engineering analyzes refactoring patterns that restructure object-oriented generalization and inheritance hierarchies. Misused inheritance produces fragile base class anomalies and bloated superclasses that violate the Liskov Substitution Principle. Students study Pull Up Method and Pull Up Field, which consolidate identical behavior from subclasses into a common superclass to eliminate duplication, and their counterparts Push Down Method and Push Down Field, which relegate specialized features only to subclasses that require them. The lecture covers Extract Superclass, Form Template Method, and critically, Replace Inheritance with Delegation, showing how favor-composition-over-inheritance design principles decouple rigid subclass relationships and build adaptable software architectures. Analytical exercises and architectural traces help students prepare thoroughly for Virtual University midterm and final term examinations. The curriculum systematically aligns theoretical software evolution principles with practical source code modernization across industrial codebases. Reviewing the accompanying lecture handouts and metric tables reinforces understanding of coupling, cohesion, and architectural decay. Consistent evaluation of control flow graphs, call graph hierarchies, and database schemas ensures robust preparation for academic assessments. Students investigate the trade-offs between system replacement, wrapping legacy components, and iterative code refactoring transformations. The discussion highlights how Lehman laws of evolution, system complexity growth, and declining quality necessitate continuous code restructuring. Key concepts including static program analysis, dynamic execution tracing, and characterization test safety nets are thoroughly demystified. The lecture details classical object-oriented re-engineering patterns demonstrated across standard enterprise software architectures. Structured refactoring methodologies are demonstrated using Martin Fowler catalogs, method extraction, and polymorphism replacement. Software quality attributes, maintainability index equations, and technical debt principal valuations are evaluated alongside empirical benchmarks. Architectural recovery processes are explored through module dependency analysis, component clustering, and high-level design reconstruction. Database schema normalization, legacy record migration, and automated ETL extraction pipelines are systematically analyzed. Monolithic application decomposition strategies including service-oriented architecture (SOA) and the Strangler Fig pattern are examined in depth. Scholars examine program slicing algorithms, forward and backward dependency slices, and impact assessment for proposed modifications.