Singleton Design Pattern
Question
You want to create a singleton class by using the Singleton design pattern.
Which two statements enforce the singleton nature of the design? (Choose two.)
Answers
Explanations
Click on the arrows to vote for the correct answer
A. B. C. D. E. F.BF.
To create a singleton class, we want to ensure that only one instance of the class can be created and that the instance is globally accessible. The Singleton design pattern achieves this by providing a single point of access to the instance of the class.
To enforce the singleton nature of the design, we need to follow the following rules:
Make the constructor private: This prevents other classes from instantiating the Singleton class by restricting access to the constructor. The constructor is only accessible within the Singleton class itself, ensuring that no other instance of the class can be created.
Make the single instance created static and final: This creates a single instance of the Singleton class that is accessible to all other classes. The static keyword ensures that the instance is associated with the class, not an instance of the class. The final keyword ensures that the instance cannot be re-assigned, making it a constant value.
Therefore, options B and F are the two correct statements that enforce the singleton nature of the design. Option A is incorrect as making the class static is not necessary to create a Singleton class. Option C is not necessary as overriding equals() and hashCode() methods of the java.lang.Object class is not related to the Singleton design pattern. Option D is incorrect because we do not want to use a public reference to point to the single instance, as this would allow other classes to create additional instances of the Singleton class. Option E is not necessary for creating a Singleton class, but if we do want to make our Singleton class Serializable, we should implement the Serializable interface.
