Java - Libgdx : Check user's input in a textfield?

My if..else statement:

if(réponse.getText().equals("")){
            réponse.setText("");
        } else if(réponse.getText().equals("riviere")){
            game.setScreen(new Stage1(game));
            music.stop();
        }
        else if(!réponse.getText().equals("riviere")){
            ecrireLeTexte = true;
        }

I created a textfield and then straight away check what's in it but I'm afraid the user can't type anything before the textfield check's...

so how to check the user's input after it's typing ?