Suggest an editImprove this articleRefine the answer for “How does OCP help avoid bugs when making changes?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**OCP helps avoid bugs when making changes** because new behavior is added through extension rather than by changing already working code. **Key point:** OCP reduces the number of bugs because new behavior is introduced without changing old code, and bugs mostly appear where old code gets rewritten.Shown above the full answer for quick recall.Answer (EN)ImageOCP helps avoid bugs when making changes because **new behavior is added through extension rather than by changing already working code**. This reduces the chance of unintentionally breaking existing logic. In detail: ## 1. Stable code is left untouched Bugs most often appear when a developer changes a part of the system that has already been tested. If a module is closed for modification, its internal logic remains unchanged, so there is no risk of introducing an error there. ## 2. New requirements are implemented in isolated modules When extension happens through new classes or implementations, changes are concentrated only in the new area of code. Old behavior is not touched and is not put at risk. ## 3. Fewer entry points where an error can occur When OCP is violated, adding new behavior requires edits in several places, including the central code (for example, long `if/else` chains). When OCP is followed, only one zone changes - a new interface implementation or strategy. ## 4. Testing becomes simpler A new functional block can be tested separately, without retesting the whole system. Stable code remains covered by earlier tests, and the new code is covered separately, which reduces the chance of missing a bug. ## 5. The cascade effect is eliminated If extension forces existing code to be modified, errors can propagate further through the chain of dependencies. When OCP is followed, dependencies stay the same, and there is no cascade effect. Summary: **OCP reduces the number of bugs because new behavior is introduced without changing old code, and bugs mostly appear where old code gets rewritten.**For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.