Top 10 Singleton Interview Questions and Answers

Static is a keyword used to declare a variable or method that belongs to the class. Singleton is a design pattern that restricts the instantiation of a class to one object.

• Static members are accessed using the class name, while Singleton objects are accessed using a getInstance() method.

• Static members are shared among all instances of a class, while Singleton objects are unique.

• Static members are initialized when the class is loaded, while Singleton objects are initialized wh...read more

A Singleton class is a class that can only have one instance at a time.

• It restricts the instantiation of a class to a single object.

• It provides a global point of access to that instance.

• It is often used in situations where a single object is required to coordinate actions across a system.

• Example: Database connection manager, Configuration manager, Logger manager.

Singleton is a design pattern that restricts the instantiation of a class to one object and provides a global point of access to that instance.

• Ensure private constructor to prevent instantiation of multiple objects.

• Provide a static method to access the single instance.

• Use a static variable to hold the single instance.

• Implement a private clone method to prevent cloning of the instance.

Singleton pattern ensures a class has only one instance, while observer pattern allows multiple objects to listen and react to changes in a subject.

• Singleton pattern involves a private constructor, a static method to access the instance, and a static variable to hold the instance.

• Observer pattern involves a subject that maintains a list of observers, and notifies them of any state changes.

• Example of singleton pattern: DatabaseConnection class with a private constructor, getIn...read more

Singleton services can be made multiton by maintaining a map of instances with unique keys.

• Create a map to store instances with unique keys

• Use a factory method to retrieve instances based on keys

• Ensure that only one instance is created per key

Singleton is a design pattern that restricts the instantiation of a class to one object, while an abstract class cannot be instantiated and is meant to be subclassed.

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

• Abstract classes cannot be instantiated on their own and are designed to be subclassed to provide implementation details.

• Singleton pattern is commonly used for managing resources that are shared across the applicat...read more

Thread safe singleton can be implemented using double-checked locking or synchronized block.

• Use double-checked locking to ensure only one instance is created.

• Use synchronized block to make sure only one thread can access the creation of instance at a time.

• Example: public class ThreadSafeSingleton { private static volatile ThreadSafeSingleton instance; private ThreadSafeSingleton(){} public static ThreadSafeSingleton getInstance() { if (instance == null) { synchronized (Thread...read more

Singleton ensures a class has only one instance, while Abstract Factory provides an interface for creating families of related objects.

• Singleton pattern restricts the instantiation of a class to one object, ensuring there is only one instance of the class.

• Abstract Factory pattern provides an interface to create families of related or dependent objects without specifying their concrete classes.

• Singleton pattern can be implemented using a private constructor, static method to a...read more

Singleton and static are both design patterns used to create objects with global access, but they differ in their implementation.

• Singleton restricts the instantiation of a class to a single object, while static allows multiple instances.

• Singleton provides a global point of access to the object, while static members are accessed through the class name.

• Singleton can be lazy-loaded, while static members are initialized at compile-time.

• Singleton can be used to maintain state acro...read more

Design patterns are reusable solutions to common problems in software design. Singleton ensures a class has only one instance, while factory creates objects without specifying the exact class.

• Design patterns are best practices for solving common software design problems.

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

• Factory pattern creates objects without specifying the exact class to be instantiated.

• Examples: Singleton - D...read more