Singleton Design Pattern || Singleton Pattern Implementation in Java смотреть онлайн

Singleton Design Pattern :
The singleton pattern is implemented using java by creating a class with a method that creates a new instance of the class if one does not exist.
If an instance already exists, it simply returns a reference to that object.
To make sure that the object cannot be instantiated any other way, the constructor is made private.

Intent:
The singleton pattern is one of the simplest design patterns: it involves only one class which is responsible to instantiate itself, in such a way that it creates only one instance.

Where to use singleton Design Pattern:
If several people have same requirement then it is not recommended to create a separate object for every requirement, instead of create only one object and reuse same object for every similar requirement so that performance and memory utilization will be improved.
This is the central idea where we used singleton design pattern

Singleton Requirement:
Consider one business requirement of an application where you need a property file which contains information regarding database configuration along with some localize values (like path to upload or download the images) so that you can modify that property file information dynamically according to your client requirements without recompiling the code.
Suppose if ten developers required this same information (may be partial or complete) then obviously instead of creating ten separate objects for that information we can add constraints (use singleton design pattern) and create a single object containing entire information of property file and reuse that object every time whenever the new request came and therefore it improve performance and memory utilization.

There are three ways through which we can achieve thread-safety in singleton design pattern.
1. Create the instance variable at the time of class loading / Use static modifier at the time of instance
creation(Early instantiation)
2. Synchronize the static method using synchronized modifier(in our example getSingletonInstance())
3. Use synchronized block (Use class level lock):