textArea = new TextArea();

textArea.focusedProperty().addListener(new ChangeListener<Boolean>(){
    @Override
    public void changed(ObservableValue<? extends Boolean> observable, Boolean oldValue, Boolean newValue) {
            if (newValue){

                System.out.println("Textfield on focus");
            } else {
                System.out.println("Textfield out focus");
            }
    }
});