import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.input.KeyEvent;
import javafx.scene.input.KeyCode;

btn.setOnKeyPressed(new EventHandler() {
        @Override
        public void handle(KeyEvent k) {
            if (k.getCode().equals(KeyCode.ENTER)) {
                doSomething();
            }
        }
});