Immutability
The property that objects don't change after creation, fundamental to functional programming. Immutability prevents side effects and simplifies concurrent programming.
Real World
Git tracks every version of your code as an immutable snapshot — rather than overwriting old files, each commit creates a new object, letting developers safely revert to any previous state.
Exam Focus
Always link immutability to thread safety in concurrency questions — state the benefit explicitly to secure the mark.
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