What is the Singleton pattern?

In software engineering, the singleton pattern is a software design pattern that restricts the instantiation of a class to one object. The concept is sometimes generalized to systems that operate more efficiently when only one object exists, or that restrict the instantiation to a certain number of objects.
A.

What is Singleton pattern in C#?

The singleton pattern is one of the best-known patterns in software engineering. Essentially, a singleton is a class which only allows a single instance of itself to be created, and usually gives simple access to that instance. There are various different ways of implementing the singleton pattern in C#.
  • What is the purpose of private constructor in C#?

    A private constructor is a special instance constructor. It is generally used in classes that contain static members only. If a class has one or more private constructors and no public constructors, other classes (except nested classes) cannot create instances of this class. For example: C#
  • What is the use of static constructors in C#?

    A static constructor is used to initialize any static data, or to perform a particular action that needs to be performed once only. It is called automatically before the first instance is created or any static members are referenced. C# class SimpleClass { // Static variable that must be initialized at run time.
  • What is the use of thread in C#?

    In C#, the System.Threading.Thread class is used for working with threads. It allows creating and accessing individual threads in a multithreaded application. The first thread to be executed in a process is called the main thread. When a C# program starts execution, the main thread is automatically created.
B.

When Singleton pattern is used?

In Java the Singleton pattern will ensure that there is only one instance of a class is created in the Java Virtual Machine. It is used to provide global point of access to the object. In terms of practical use Singleton patterns are used in logging, caches, thread pools, configuration settings, device driver objects.
  • Can a static class be inherited in Java?

    Static methods are inherited in Java but they don't take part in polymorphism. If we attempt to override the static methods they will just hide the superclass static methods instead of overriding them. Static method is inherited in subclass but it is not polymorphism.
  • What is a factory design pattern?

    In class-based programming, the factory method pattern is a creational pattern that uses factory methods to deal with the problem of creating objects without having to specify the exact class of the object that will be created.
  • What is a singleton class?

    A singleton is a class that allows only a single instance of itself to be created and gives access to that created instance. It contains static variables that can accommodate unique and private instances of itself. It is used in scenarios when a user wants to restrict instantiation of a class to only one object.
C.

Why you should not use Singleton?

Singleton is not a pattern to wrap globals. Singleton pattern should only be used to guarantee that one and only one instance of a given class exists during run time. People think Singleton is evil because they are using it for globals. It is because of this confusion that Singleton is looked down upon.
  • How is priority queue implemented?

    A priority queue is different from a "normal" queue, because instead of being a "first-in-first-out" data structure, values come out in order by priority. A priority queue can be implemented using many of the data structures that we've already studied (an array, a linked list, or a binary search tree).
  • What is Heapify?

    Heapify is the process of converting a binary tree into a Heap data structure. A binary tree being a tree data structure where each node has at most two child nodes. A Heap must also satisfy the heap-order property, the value stored at each node is greater than or equal to it's children.
  • Which is the fastest sorting algorithm?

    The time complexity of Quicksort is O(n log n) in the best case, O(n log n) in the average case, and O(n^2) in the worst case. But because it has the best performance in the average case for most inputs, Quicksort is generally considered the “fastest” sorting algorithm.

Updated: 2nd October 2019

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