[Solved] You need to ensure that a class has only one instance throughout the application lifecycle, and this instance must be lazily initialized in a... Which design approach best fits this requirement? | OOP & Design Patterns

OOP & Design Patterns - Singleton Pattern - Thread Safety, Double-Checked Locking & Lazy Init

You need to ensure that a class has only one instance throughout the application lifecycle, and this instance must be lazily initialized in a thread-safe manner without incurring synchronization overhead on every access. Which design approach best fits this requirement?

AUse a simple static variable without synchronization and rely on the language's memory model.

BUse a synchronized method that creates the instance on first call, locking every time.

CCreate the instance eagerly at class loading time to avoid synchronization issues.

DImplement double-checked locking with a volatile instance variable to minimize synchronization overhead.

Step-by-Step Solution

Step 1: Understand the problem constraints
The instance must be lazily initialized and thread-safe, but synchronization overhead should be minimized.
Step 2: Evaluate each approach
Synchronized method locks on every call, causing overhead. Eager initialization is thread-safe but not lazy. Unsynchronized static variable risks multiple instances in multithreaded contexts. Double-checked locking with volatile ensures lazy init, thread safety, and minimal locking.
Final Answer:
Option D -> Option D
Quick Check:
Double-checked locking balances thread safety and performance [OK]

Quick Trick: Double-checked locking minimizes synchronization overhead [OK]

Common Mistakes:

MISTAKES

Assuming synchronized method is efficient enough
Believing eager initialization is always best
Ignoring volatile keyword necessity

Trap Explanation:

PITFALL

Synchronized methods are thread-safe but cause performance hits; eager init is thread-safe but not lazy; volatile is essential for double-checked locking correctness.

Interviewer Note:

CONTEXT

Tests candidate's understanding of thread-safe lazy initialization tradeoffs.

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Which design approach best fits this requirement?

Step 1: Understand the problem constraints

Step 2: Evaluate each approach

Final Answer:

Quick Check:

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