Difference Between Singleton Pattern and Static Class in Java

In Java, the Singleton pattern and static classes are employed to control instance creation and access to class-level behavior, but they serve distinct purposes and possess different characteristics.

Singleton Pattern

The Singleton pattern in Java is a design pattern that guarantees the existence of only one instance of a class and provides a centralized access point to that instance. It is used when there should be exactly one instance of a class available to all parts of the application. Such scenarios often require a shared configuration, logging object, or resource pool that must be consistent and globally accessible.

The Singleton design pattern can be achieved by:

• Hiding the Constructors: Declaring all constructors of the singleton class as private so that the outer classes cannot create objects of the singleton class. Private constructors not only restrict the instantiation but also give control of the instantiation to the class itself.
• Using getInstance() Method: The method returns only one instance of the class. It will be the global access point to that only instance of the class.
• Private static variable instance of the same type as your singleton class, which will store the only instance of the class.

The Singleton pattern can have both static and instance members, allowing flexibility in its implementation. Its main goal is to offer controlled, thread-safe access to resources that should not be duplicated.

Example: Singleton Design Pattern

Output:

 Singleton instance created Hello from Singleton! true 

Static Class

A static class is a class that contains only static members. All class instances share static members, and subclasses cannot override them. In Java, only nested (inner) classes can be declared static; outer classes cannot be static. Static classes are a convenient way of grouping classes together. Java does not allow you to create top-level static classes; only nested (inner) classes. That is why a static class is also known as a static inner class or static nested class.

Example: Static Class

Output:

 Value of myVariable: 32 Value of myVariable: 32 It is the Inner Class Constructor Value of myVariable from inside Inner Class: 32 

Difference Between Singleton Pattern and Static Class

Singleton Pattern and Static Class MCQs

1. Which of the following statements is true about the Singleton Pattern?

1. Singleton classes cannot be inherited
2. Singleton classes allow only one instance of the class to be created
3. Singleton classes can contain only static methods
4. Singleton pattern violates object-oriented principles

2. Which of the following is not a characteristic of a Static Class in Java?

1. Cannot be instantiated
2. Supports polymorphism
3. All members are static
4. Cannot be extended

3. How is a Singleton instance typically accessed in Java?

1. Using the new keyword
2. Through a public constructor
3. Through a static getInstance() method
4. Direct access through class name

4. Which of the following is true about static classes in Java?

1. They are lazily initialized
2. They follow OOP principles closely
3. They consume memory only when needed
4. They are loaded when the class is first referenced

5. Which feature is supported by Singleton but not by a Static Class?

1. Having Static Methods
2. Supporting Inheritance
3. Being Accessed Using the Class Name
4. Initialization At Class Load Time