Key Takeaways: Code Review and Static Analysis
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Code review catches 60-90% of defects — more than testing alone. The combination of review and testing is the most effective defect-detection strategy available.
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Eight common COBOL defect patterns account for the majority of production bugs: uninitialized fields, missing scope terminators, wrong PIC clauses, unreachable code, incorrect PERFORM THRU ranges, decimal alignment errors, unchecked file status, and GO TO spaghetti.
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Coding standards prevent defects and ensure consistency. A good standard covers naming conventions, structure rules (paragraph length, nesting depth), documentation requirements, and error handling patterns.
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Static analysis tools automate defect detection. SonarQube, IBM ADDI, and even GnuCOBOL compiler warnings can identify bugs, code smells, and standards violations without executing the program.
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Cyclomatic complexity quantifies testing difficulty. A paragraph with complexity above 20 is difficult to test thoroughly; above 50, it is effectively untestable and should be refactored.
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Dead code is a hidden cost. Unreachable paragraphs, unused data items, and commented-out code blocks confuse developers, create false dependencies, and increase maintenance burden. Remove them opportunistically.
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Copy/paste duplication should be refactored into copybooks, shared paragraphs, or subprograms. Duplicated code means duplicated bugs — and duplicated fix effort.
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The code review checklist is your safety net. A structured checklist ensures that reviewers consistently check for known defect patterns rather than relying on ad-hoc inspection.
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Technical debt can be quantified in person-hours of remediation effort. This data drives prioritization — fix the highest-debt, most-frequently-modified programs first.
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The "boy scout rule" makes incremental improvement sustainable. Leave every program better than you found it. Over time, quality improves without dedicated refactoring projects.