Given a base class Instrument with a virtual method Play() and derived classes Guitar and Piano overriding Play(), which code snippet correctly demonstrates runtime polymorphism when calling Play() on a list of instruments?
hard🚀 Application Q8 of 15
C Sharp (C#) - Polymorphism and Abstract Classes
Given a base class Instrument with a virtual method Play() and derived classes Guitar and Piano overriding Play(), which code snippet correctly demonstrates runtime polymorphism when calling Play() on a list of instruments?
AList<Instrument> instruments = new List<Instrument> { new Guitar(), new Piano() }; foreach (var inst in instruments) { inst.Play(); }
BList<Guitar> instruments = new List<Guitar> { new Guitar(), new Piano() }; foreach (var inst in instruments) { inst.Play(); }
CList<Instrument> instruments = new List<Instrument> { new Guitar(), new Piano() }; foreach (Guitar inst in instruments) { inst.Play(); }
DList<Instrument> instruments = new List<Instrument> { new Guitar(), new Piano() }; foreach (var inst in instruments) { Instrument.Play(); }
Step-by-Step Solution
Solution:
Step 1: Understand polymorphic collection
To use runtime polymorphism, store derived objects in a base class collection.
Step 2: Analyze options
List<Instrument> instruments = new List<Instrument> { new Guitar(), new Piano() }; foreach (var inst in instruments) { inst.Play(); } correctly uses a List<Instrument> holding Guitar and Piano objects and calls Play() polymorphically.
Step 3: Identify errors in other options
List<Guitar> instruments = new List<Guitar> { new Guitar(), new Piano() }; foreach (var inst in instruments) { inst.Play(); } uses List<Guitar> but adds Piano (invalid). List<Instrument> instruments = new List<Instrument> { new Guitar(), new Piano() }; foreach (Guitar inst in instruments) { inst.Play(); } casts to Guitar in foreach, causing invalid cast. List<Instrument> instruments = new List<Instrument> { new Guitar(), new Piano() }; foreach (var inst in instruments) { Instrument.Play(); } calls Instrument.Play() statically, not polymorphically.
Final Answer:
Option A -> Option A
Quick Check:
Use base class list and virtual methods [OK]
Quick Trick:Use base class list and virtual methods [OK]
Common Mistakes:
MISTAKES
Using derived class list for multiple derived types
Incorrect casting in foreach
Calling base class method statically
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