Singleton pattern in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Singleton pattern?

The Singleton pattern ensures a class has only one instance and provides a global point of access to it.

beginner

Why use the Singleton pattern in system design?

To control resource usage by limiting the number of instances, and to provide a single shared object accessible globally.

intermediate

How does the Singleton pattern prevent multiple instances?

By making the constructor private and providing a static method that returns the single instance, creating it only once.

intermediate

What is a common problem with Singleton in multithreaded environments?

Multiple threads may create multiple instances if access is not synchronized properly, breaking the Singleton guarantee.

intermediate

Name one way to make Singleton thread-safe.

Use synchronized access or double-checked locking to ensure only one instance is created even with multiple threads.

What does the Singleton pattern guarantee?

A Only one instance of a class exists

B Multiple instances of a class exist

C No instances of a class exist

D Instances are created on demand without limit

Singleton ensures only one instance of a class exists and provides global access to it.

How is the Singleton instance usually accessed?

A Through a public static method

B By creating new objects directly

C By subclassing the Singleton

D Through multiple constructors

Singleton provides a public static method to get the single instance.

What problem can occur if Singleton is not thread-safe?

A The instance will be destroyed

B Multiple instances may be created

C No instance will be created

D The instance will be shared incorrectly

Without thread safety, multiple threads can create multiple instances, breaking the Singleton pattern.

Which of these is NOT a typical Singleton feature?

A Private constructor

B Global access method

C Static instance variable

D Multiple public constructors

Singleton uses a private constructor to prevent multiple instances, so multiple public constructors are not allowed.

Which technique helps make Singleton thread-safe?

A Using public constructors

B Ignoring synchronization

C Double-checked locking

D Creating multiple instances

Double-checked locking ensures only one instance is created even with multiple threads.

Explain the Singleton pattern and why it is useful in system design.

Think about how you would share one resource safely across a system.

Describe how to implement a thread-safe Singleton.

Consider what happens when multiple threads try to create the instance at the same time.