If-statment didn't work correctly [duplicate]

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• How do I compare strings in Java? 23 answers

i have some problems because i dont undestand why my checking with if didn't work.

List<Cards> myCardsList = dataBaseAdapter.getData();

    int a = myCardsList.size();

    for (int i = 0; i < a; i++) {


        if (!myCardsList.get(i).getCardInBaseId().toString().equals("a")) {

            if(myCardsList.get(i).getCardInBaseId().toString() == idTest){
                Toast.makeText(getApplicationContext(),"Card already added" ,Toast.LENGTH_LONG).show();
            }
        }
    }

i have List with some Strings like names, cardInBaseId etc, now i need to check in this array if this cardInBaseId = String idTEst. if cardInBaseId != idtest i need to do some code

P.S cardidInBase can be = "a" , or some number (i put it value a because if i try to do this method when cardInBaseId == null i have always NullPointedExeption

So help me pls and explain why my if didn't work correctly