nullpointerexception - Android FileoutputStream NullPOinter Exception -

public class database_wrapper {       users_database u_db;       sqlitedatabase sql_db;      context context;      database_wrapper(context context)     {         u_db = new users_database(context);         sql_db = u_db.getwritabledatabase();     }      public long insert_data(list<name_holder> list)     {         contentvalues contentvalues = new contentvalues();          long error_code = 0;         string filename;         for(int = 0; < list.size(); i++) {             filename = "test_image";//string.valueof(list.get(i).id);             log.v("datadata",filename);             if(list.get(i)._bmp == null)             {                 log.v("datadata", "no image");             }             try {                 bytearrayoutputstream bytes = new bytearrayoutputstream();                 fileoutputstream fo;                 list.get(i)._bmp.compress(bitmap.compressformat.jpeg, 100, bytes);                 fo = context.openfileoutput(filename, context.mode_private);                  fo.write(bytes.tobytearray());                 // remember close file output                 fo.close();             } catch (exception e) {                 e.printstacktrace();                 log.v("datadata", e.tostring());                 filename = "null";             }              contentvalues.put(u_db.id, list.get(i).id);             log.v("datadata1", string.valueof(list.get(i).id));             contentvalues.put(u_db.name, list.get(i).name);             log.v("datadata2", list.get(i).name);             contentvalues.put(u_db.distance, list.get(i).distance);             log.v("datadata3", string.valueof(list.get(i).distance));             contentvalues.put(u_db.avatar, filename);             log.v("datadata4", filename);             contentvalues.put(u_db.age, list.get(i).age);             log.v("datadata5", list.get(i).age);             contentvalues.put(u_db.sex, list.get(i).sex);             log.v("datadata6", list.get(i).sex);             contentvalues.put(u_db.orient, list.get(i).orient);             log.v("datadata7", string.valueof(list.get(i).orient));              long j = sql_db.insert(u_db.table_name, null, contentvalues);             if (j < 0)                 error_code = j;              int y = (int)j;             log.v("datadata", string.valueof(y));         }         return error_code;     } 

this code gives me exception: java.lang.nullpointerexception: attempt invoke virtual method 'java.io.fileoutputstream android.content.context.openfileoutput(java.lang.string, int)' on null object reference need help.. did wrong? logcat first itiration:

07-23 06:45:56.686    8796-8915/? v/datadata﹕ test_image 07-23 06:45:56.696    8796-8915/? v/datadata﹕ java.lang.nullpointerexception: attempt invoke virtual method 'java.io.fileoutputstream android.content.context.openfileoutput(java.lang.string, int)' on null object reference 07-23 06:45:56.696    8796-8915/? v/datadata1﹕ 2 07-23 06:45:56.696    8796-8915/? v/datadata2﹕ `h jvkv h  h r 07-23 06:45:56.696    8796-8915/? v/datadata3﹕ 0 07-23 06:45:56.696    8796-8915/? v/datadata4﹕ null 07-23 06:45:56.696    8796-8915/? v/datadata5﹕ 90 07-23 06:45:56.696    8796-8915/? v/datadata6﹕ male 07-23 06:45:56.696    8796-8915/? v/datadata7﹕ 0 07-23 06:45:56.706    8796-8915/? v/datadata﹕ -1 

you didn't initialize context object thats why getting nullpointerexception.

initialize context object inside database_wrapper() constructor method.

database_wrapper(context context) {      this.context = context;      u_db = new users_database(context);     sql_db = u_db.getwritabledatabase(); }