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