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As am very new to Android I've red a lot about singleton classes in java. I completely understand the concept of singleton, but I'm really confused where to use it in Android, I have used it neither yet.Could you guide or explain me with a real example where to use or in which case should I use a singleton class?

It's depend on your projects and how you implement your MVC or MVP structure. You can use any design pattern in your code and your classes where you need. This is an example of singleton class:
public class Singleton {
private static Singleton mInstance = null;
private String mString;
private Singleton(){
mString = "Hi!";
}
public static Singleton getInstance(){
if(mInstance == null)
{
mInstance = new Singleton();
}
return mInstance;
}
public String getString(){
return this.mString;
}
public void setString(String value){
mString = value;
}
This class create once and when you need an object of this class just use object was created before

Take a look at this gist : https://gist.github.com/Akayh/5566992
it works but it was done very quickly :
MyActivity : set the singleton for the first time + initialize mString attribute ("Hello") in private constructor and show the value ("Hello")
Set new value to mString : "Singleton"
Launch activityB and show the mString value. "Singleton" appears...

It totally depends on your need and requirement thought we use it in almost every project to make our life easier.
In android I use singleton of DatabaseHelper so that I don't have to be extra careful about about the opening and closing the database again and again and dealing with the database lock and concurrent accesses of the database etc.
Check this :-http://www.androiddesignpatterns.com/2012/05/correctly-managing-your-sqlite-database.html
2.Then I use to manage SharedPreferences to store the sharedpreferences it will be a lot easier to maintain the code and I don't I have to go around and around to see check the keys value and all.
Check this :-https://medium.com/#ali.muzaffar/android-sharedpreferences-singleton-to-make-life-easier-f1d802b6cd8e.
3.Then I use it when I want to access an object anywhere in the application and which is frequently required.
Hope you have got the little bit idea where to use.

most use in Volley API When you want one object from Volley in your app
ex: for Singleton this example explain you get one RequestQueue in your App
public class VolleySingleton {
private static VolleySingleton singleton;
private RequestQueue requestQueue;
private VolleySingleton(){
requestQueue= Volley.newRequestQueue(MyApplication.getAppContext());
}
public static VolleySingleton getInstance(){
if(singleton==null)
singleton=new VolleySingleton();
return singleton;
}
public void setRequestQueue(RequestQueue requestQueue)
{
this.requestQueue = requestQueue;
}
public RequestQueue getRequestQueue() {
return requestQueue;
}
}