Singleton in Android

I have followed this link and successfully made singleton class in Android. http://www.devahead.com/blog/2011/06/extending-the-android-application-class-and-dealing-with-singleton/

Problem is that i want a single object. like i have Activity A and Activity B. In Activity A I access the object from Singleton class. I use the object and made some changes to it.

When I move to Activity B and access the object from Singleton Class it gave me the initialized object and does not keep the changes which i have made in Activity A. Is there any other way to save the changing? Please help me Experts. This is MainActivity

public class MainActivity extends Activity {
    protected MyApplication app;        
    private OnClickListener btn2=new OnClickListener() {    
        @Override
        public void onClick(View arg0) {
            Intent intent=new Intent(MainActivity.this,NextActivity.class);
            startActivity(intent);              
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Get the application instance
        app = (MyApplication)getApplication();

        // Call a custom application method
        app.customAppMethod();

        // Call a custom method in MySingleton
        Singleton.getInstance().customSingletonMethod();

        Singleton.getInstance();
        // Read the value of a variable in MySingleton
        String singletonVar = Singleton.customVar;

        Log.d("Test",singletonVar);
        singletonVar="World";
        Log.d("Test",singletonVar);

        Button btn=(Button)findViewById(R.id.button1);
        btn.setOnClickListener(btn2);
    }

}

This is NextActivity

public class NextActivity extends Activity {

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_next);

            String singletonVar = Singleton.customVar;

            Log.d("Test",singletonVar);
        }
  }

Singleton Class

public class Singleton
{
    private static Singleton instance;

    public static String customVar="Hello";

    public static void initInstance()
    {
    if (instance == null)
    {
      // Create the instance
      instance = new Singleton();
    }
    }

    public static Singleton getInstance()
    {
     // Return the instance
     return instance;
     }

     private Singleton()
     {
     // Constructor hidden because this is a singleton
     }

     public void customSingletonMethod()
     {
     // Custom method
     }
 }

and MyApplication

public class MyApplication extends Application
    {
    @Override
    public void onCreate()
    {
    super.onCreate();

     // Initialize the singletons so their instances
     // are bound to the application process.
     initSingletons();
     }

     protected void initSingletons()
     {
     // Initialize the instance of MySingleton
     Singleton.initInstance();
     }

     public void customAppMethod()
     {
     // Custom application method
    }
}

When i run this code, i get Hello which i have initialized in Singleton then World which i gave it in MainActivity and again shows Hello in NextActivity in logcat. I want it to show world again in NextActivity. Please help me to correct this.

Tip: To create singleton class In Android Studio, right click in your project and open menu:

New -> Java Class -> Choose Singleton from dropdown menu

EDIT :

The implementation of a Singleton in Android is not "safe" (see here) and you should use a library dedicated to this kind of pattern like Dagger or other DI library to manage the lifecycle and the injection.

Could you post an example from your code ?

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 is simple, as a java, Android also supporting singleton. -

Singleton is a part of Gang of Four design pattern and it is categorized under creational design patterns.

-> Static member : This contains the instance of the singleton class.

-> Private constructor : This will prevent anybody else to instantiate the Singleton class.

-> Static public method : This provides the global point of access to the Singleton object and returns the instance to the client calling class.

1. create private instance
2. create private constructor

3. use getInstance() of Singleton class

   public class Logger{
   private static Logger   objLogger;
   private Logger(){
   
           //ToDo here
   
   }
   public static Logger getInstance()
   {
       if (objLogger == null)
      {
         objLogger = new Logger();
      }
      return objLogger;
      }
   
   }
   

while use singleton -

Logger.getInstance();