User.java

import android.content.Context;
import android.content.SharedPreferences;
import android.preference.PreferenceManager;

public class User {String username, value;
    Boolean status;
    SharedPreferences sp;
    SharedPreferences.Editor editor;

    public void setUsername(Context context, String username){
        sp = PreferenceManager.getDefaultSharedPreferences(context);
        editor = sp.edit();
        editor.putString("username", username);
        editor.commit();
    }

    public String getUsername(Context context){
        sp = PreferenceManager.getDefaultSharedPreferences(context);
        value = null;
        username = sp.getString("username", value);
        return username;
    }

    public Boolean isLogin(Context context){
        sp = PreferenceManager.getDefaultSharedPreferences(context);
        value = null;
        username = sp.getString("username", value);
        if (username!=null){
            status = true;
        }else {
            status = false;
        }
        return status;
    }

    public void logOut(Context context){
        sp = PreferenceManager.getDefaultSharedPreferences(context);
        editor = sp.edit();
        editor.putString("username", null);
        editor.commit();
    }

}