What is the best way to create singleton class in Java?

Eager initialization: In eager initialization, the instance of Singleton Class is created at the time of class loading, this is the easiest method to create a Singleton class. By making the constructor as private you are not allowing other class to create a new instance of the class you want to create the Singleton.

How do I know if a class is singleton?

So, simply call the method which is returning your expected singleton type of object and call hashcode() method on it. If it prints the same hashcode each time, it means it’s singleton, else it’s not.

What is singleton instance?

In software engineering, the singleton pattern is a software design pattern that restricts the instantiation of a class to one “single” instance. This is useful when exactly one object is needed to coordinate actions across the system.

What is difference between singleton and static class in Java?

The singleton, like any other instance of a class, lives on the heap. To its advantage, a huge singleton object can be lazily loaded whenever required by the application. On the other hand, a static class encompasses static methods and statically bound variables at compile time and is allocated on the stack.

What is difference between static and singleton?

While a static class allows only static methods and and you cannot pass static class as parameter. A Singleton can implement interfaces, inherit from other classes and allow inheritance. While a static class cannot inherit their instance members. So Singleton is more flexible than static classes and can maintain state.

Can we serialize singleton class?

Suppose if you serialize the Singleton class, and then again de-serialize that object, it will create a new instance, hence deserialization will break the Singleton pattern. The below code is used to illustrate how the Singleton pattern breaks with deserialization. Implements Serializable interface for Singleton Class.

Where is singleton class used?

It is used where only a single instance of a class is required to control the action throughout the execution. A singleton class shouldn’t have multiple instances in any case and at any cost. Singleton classes are used for logging, driver objects, caching and thread pool, database connections.

How many instances can a single class have?

Only one instance can be created from a single class.

Can we make singleton class final?

Singleton classes, if properly implemented, do not need to be declared final in order to not be extended. Since all the constructors of the singleton class are private, you can’t extend that class. In fact, singleton classes are effectively final.