Singleton Pattern In Android

This blog defines the most widely used Singleton pattern in Android.

In this blog, I am describing the most important concept of Android Development which is the Singleton Pattern. It is also a very important interview question that is asked to Android Developers.  

 

What is Singleton in Android?

 

It is basically a design pattern we use in Android Application Development. 

 

How it is achieved?

 

It is achieved by simply making the constructor of a class as private.

 
Purpose of this pattern?

 

This pattern is basically used to restrict a class of making new instances. We use this pattern when we want a class to not be able to create a new instance in any way.

 

Making a singleton is not difficult but making it perfect is a thing that is a little challenging.  

 

Below is the example of a perfect singleton.

pubic class SingletonClass{
   private static SingletonClass sClassInstance;
   private SingletonClass(){
      if(sClassInstance != null){
         throw new RuntimeException("getInstance() method will be used to get single instance of this class");
      }
   }
   public synchronized static SingletonClass getInstance(){
      if(sClassInstance == null){
         sClassInstance = new SingletonClass();
      }
   return sClassInstance;
   }
}

In this examle, a class is defined and named as SingletonClass, which is basically a singleton class. This class contains a private static instance of class, a private constructor, and a synchronized static method getInstance(). 

 

Why do we use synchronized?

 

It is necessary to use while working in a multithreaded environment. It prevents two threads creating NEW INSTANCE for each. There may be a time when two threads access the method at the same time and if we will not use synchronized Singleton pattern, the rule will break and a new instance will be created in the heap which is an extra load and nothing else. To avoid this, it is necessary to use synchronized with an instance method.