Singleton objects can be created in two ways. Question: In how many ways can you create singleton pattern in Java?
Clients may only use the accessor function to manipulate the Singleton. Define all constructors to be protected or private. Do "lazy initialization" (creation on first use) in the accessor function. 
Define a public static accessor function in the class. 
Define a private static attribute in the "single instance" class.Implementation in Java: Step 1: Creating a Singleton Class. Global access is not otherwise provided for.Ownership of the single instance cannot be reasonably assigned.Singleton encapsulates "just-in-time initialization" of the objectĬonditions: Singleton should only be considered if following criteria are satisfied:.Singleton ensures that a class has only one instance, and provide a global point of access to this instance.Singleton pattern is one of the simplest design pattern.It is used when an application needs one, and only one, instance of an object of class. Question: What is a Singleton design pattern? Makes it almost impossible to subclass a Singleton.
Creates tightly coupled code that is difficult to test. Encourages using a global shared instance which prevents an object and resources used by this object from being deallocated. Violates Single Responsibility Principle (SRP) by controlling their own creation and lifecycle. when the sole instance should be extensible by subclassing, and clients should be able to use an extended instance without modifying their code. There must be exactly one instance of a class, and it must be accessible to clients from a well-known access point. When to use Singleton? Use the Singleton when It ensures that a class has only one instance, and provides a global point of access to it.
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