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Given a decorator chain where the final cost returned is 8, and you know the base object cost is 5, and two decorators add 1 and 2 respectively, which decorator was applied last?

hard🔄 Reverse Engineer Q9 of Q15

OOP & Design Patterns - Decorator Pattern - Wrapping Behaviour Without Subclassing

Given a decorator chain where the final cost returned is 8, and you know the base object cost is 5, and two decorators add 1 and 2 respectively, which decorator was applied last?

AThe decorator adding 2 was applied last

BThe decorator adding 1 was applied last

CBoth decorators were applied simultaneously

DCannot determine from given information

Step-by-Step Solution

Solution:

Step 1: Calculate total cost
Base cost 5 + 1 + 2 = 8 matches final cost.
Step 2: Understand decorator call order
Last applied decorator adds its cost last in the call chain.
Step 3: Identify last decorator
Since final cost includes +2 last, decorator adding 2 was applied last.
Final Answer:
Option A -> Option A
Quick Check:
Decorator call order affects cost accumulation order [OK]

Quick Trick: Last decorator's cost added last in chain -> final increment [OK]

Common Mistakes:

MISTAKES

Assuming order doesn't affect cost
Confusing first and last decorator
Ignoring additive nature of decorators

Trap Explanation:

PITFALL

Candidates often ignore that decorator order affects final cost calculation.

Interviewer Note:

CONTEXT

Tests reasoning backwards through decorator call chain.

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