private void nextStep(){
        if(currentStep < 0 && currentStep >= paneSteps.length){
            return;
        }
        if(check(currentStep)){
            GUIUtil.switchPane(paneSteps[currentStep], paneSteps[++currentStep]);
            if(currentStep > 0){
                bt_pre.setVisible(true);
            }
            if(currentStep == paneSteps.length - 1){
                bt_next.setText("Finish");
            }
        }else{
            JOptionPane.showMessageDialog(null, "Invalid Input!", "Error", JOptionPane.ERROR_MESSAGE);
        }
    }