Top 30 Singleton Interview Questions and Answers 2024

To create a singleton class in a multi-threaded environment, we can use double-checked locking or synchronized block.

• Use double-checked locking to minimize the use of synchronization and improve performance.

• In double-checked locking, check if the instance is null, then synchronize the block and create the instance.

• Use volatile keyword to ensure visibility of the instance across threads.

• Alternatively, use synchronized block to create a thread-safe singleton class.

• In synchroniz...read more

Singleton class ensures only one instance is created, while static class allows multiple instances.

• Singleton class restricts instantiation of a class to a single object.

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

• It is useful when only one instance of a class is required throughout the system.

• Singletons can be lazy-loaded or eagerly-loaded.

• Static classes allow multiple instances and are not suitable for maintaining state.

• Static classes are useful for utility function...read more

A singleton class is a class that can only be instantiated once. It is important to secure it in a multi-threading environment.

• Create a private constructor to prevent external instantiation

• Create a private static instance of the class

• Create a public static method to return the instance

• Use synchronized keyword to ensure thread safety

• Consider using double-checked locking to improve performance

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.

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

To create thread singleton, use double-checked locking or enum.

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

• Alternatively, use enum to create a singleton with thread safety

• Ensure proper synchronization to avoid race conditions

Singleton class is a design pattern that restricts the instantiation of a class to one object, while circuit breaker pattern is a design pattern used in software development to prevent cascading failures.

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

• Circuit breaker pattern is used to detect failures and prevent them from causing further damage by temporarily stopping the execution of a function or service.

• Example of Sin...read more

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

Factory pattern is used to create objects without exposing the instantiation logic to the client, while Singleton pattern ensures a class has only one instance and provides a global point of access to it.

• Factory pattern is used to create objects based on a common interface, without specifying the exact class of the object being created.

• Singleton pattern restricts the instantiation of a class to one object, ensuring that all requests for the object return the same instance.

• Fac...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

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

• Create a private constructor to prevent instantiation from outside the class.

• Create a private static instance of the class.

• Create a public static method to get the instance of the class.

• Ensure thread safety by using synchronized keyword or static initializer.

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

Static class cannot be instantiated and has only static members, while singleton class allows only one instance to be created and provides a global point of access to it.

• Static class cannot be inherited, while singleton class can be

• Static class members are accessed using class name, while singleton class instance is accessed using getInstance() method

• Static class is used for utility classes, while singleton class is used for classes that need to maintain state

• Example of stati...read more

Singleton class allows only one instance to be created, while static class cannot be instantiated and all members are static.

• Singleton class can have instance methods and properties, while static class can only have static members.

• Singleton class can be lazy loaded, while static class is eagerly loaded.

• Singleton class can be implemented using a static property or method to return the single instance, while static class cannot be instantiated.

• Example: Singleton class for datab...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 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

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

• Singleton pattern is used when we need to ensure that only one instance of a class is created and that instance can be accessed globally.

• The constructor of a singleton class is always private to prevent direct instantiation.

• A static method is used to access the singleton instance.

• Example: public class Singleton { private static Singleton instance = new Singleton(); private Singleton() {} public static Single...read more

Static class is a class that cannot be instantiated and is used for grouping related methods and properties. Singleton class is a class that can only have one instance and provides a global point of access to it.

• Static class cannot be instantiated, while singleton class can have only one instance.

• Static class is used for grouping related methods and properties, while singleton class provides a global point of access to its instance.

• Static class members are accessed using the ...read more

Singleton class ensures only one instance of a class is created and provides a global point of access to it.

• Create a private constructor to prevent direct instantiation of the class

• Create a private static instance of the class

• Create a public static method to get the instance of the class

• Ensure thread safety by using synchronized keyword or static initialization

• Example: Database connection manager

A singleton class is a class that can only have one instance created throughout the lifetime of an application.

• Create a private constructor to prevent external instantiation.

• Create a private static instance of the class.

• Create a public static method to access the instance.

• Ensure thread safety by using synchronized keyword or static initializer.

• Example: public class Singleton { private static Singleton instance = null; private Singleton() {} public static synchronized Singleto...read more

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

• Singleton classes are often used for managing resources that should only have one instance, such as a database connection.

• They typically have a private constructor to prevent multiple instances from being created.

• The instance of the class is usually accessed through a static method or variable.

• Singleton classes can also implement interfaces or inherit from other classes.

• Example: Java's Runtime clas...read more

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

• Used to restrict the instantiation of a class to one object

• Provides a global point of access to that instance

• Commonly used in logging, caching, and database applications

A singleton class is a class that can only have one instance created throughout the entire application.

• Singleton classes are used when we want to restrict the number of instances of a class to one.

• They are often used in scenarios where we need to maintain a single point of control or coordination.

• For example, a logger class can be implemented as a singleton class to ensure that only one instance of the logger is created and used throughout the application.

A singleton class is a class that can only have one instance created and provides a global point of access to that instance.

• Singleton classes are often used for logging, caching, database connections, and thread pools.

• They typically have a private constructor to prevent instantiation from outside the class.

• The class itself usually provides a static method to access the single instance.

Singleton class is a class that can only have one instance and provides a global point of access to it.

• Singleton class restricts the instantiation of a class to one object.

• It provides a way to access its unique instance globally.

• Commonly used in scenarios where only one instance of a class is needed, such as database connections or thread pools.

Singleton class ensures only one instance of a class is created

• Use a private static variable to hold the instance of the class

• Provide a public static method to access the instance

• Ensure the constructor is private to prevent instantiation from outside the class

Singleton class ensures only one instance of a class is created and provides a global point of access to it.

• Use a private static variable to hold the instance of the class.

• Make the constructor private to prevent instantiation from outside the class.

• Provide a static method to access the instance, creating it if necessary.

A singleton class is a class that can only have one instance created throughout the application.

• Ensure the class has a private constructor to prevent external instantiation.

• Provide a static method to access the single instance of the class.

• Use a static variable to hold the single instance of the class.

• Example: public class Singleton { private static Singleton instance = new Singleton(); private Singleton() {} public static Singleton getInstance() { return instance; }}