如何在用户从文本字段输入内容时对输入进行计数

Question

我正在制作一个宠物兽医系统，它有这样的支付交易。每当我试图在1个jtextfield上输入并计算它，而将其他jtextfield留空时，就会弹出错误：线程中的异常"；AWT-EventQueue-0"；java.lang.NumberFormatException：空字符串

这是随附的支付交易菜单

支付交易菜单

我如何在忽略其他文本字段为空的情况下获得输入并计算它(例如，因为客户没有获得其他服务，只有咨询服务(

以下是我的附加代码：

double Qty1 = Double.parseDouble(qty_consult.getText());
double Qty2 = Double.parseDouble(qty_dogvac.getText());
double Qty3 = Double.parseDouble(qty_catvac.getText());
double Qty4 = Double.parseDouble(qty_antirabies.getText());
double Qty5 = Double.parseDouble(qty_deworm.getText());
double Qty6 = Double.parseDouble(qty_blood.getText());
double Qty7 = Double.parseDouble(qty_urinalysis.getText());
double Qty8 = Double.parseDouble(qty_skin.getText());

double addup, subTotal, subtotal,tax_ratefee, fee1, fee2, fee3, fee4, fee5, fee6, fee7, fee8;




String consult_fee = String.format("%.2f", price_consultfee);
price_consult.setText(consult_fee);

String vac_fee = String.format("%.2f", price_vacfee);
price_vac.setText(vac_fee);

String vac2_fee = String.format("%.2f", price_vac2fee);
price_vac2.setText(vac2_fee);
String rabies_fee = String.format("%.2f", price_rabiesfee);
price_rabies.setText(rabies_fee);
String deworm_fee = String.format("%.2f", price_dewormfee);
price_deworm.setText(deworm_fee);
String cbc_fee = String.format("%.2f", price_cbcfee);
price_cbc.setText(cbc_fee);
String urine_fee = String.format("%.2f", price_urinefee);
price_urine.setText(urine_fee);
String skin_fee = String.format("%.2f", price_skinfee);
price_skin.setText(skin_fee);





fee1 = Qty1 * price_consultfee;
fee2 = Qty2 * price_vacfee;
fee3 = Qty3 * price_vac2fee;
fee4 = Qty4 * price_rabiesfee;
fee5 = Qty5 * price_dewormfee;
fee6 = Qty6 * price_cbcfee;
fee7 = Qty7 * price_urinefee;
fee8 = Qty8 * price_skinfee;


String sub1 = String.format("%.2f", fee1);
sub_consult.setText(sub1);

String sub2 = String.format("%.2f", fee2);
sub_vac.setText(sub2);

String sub3 = String.format("%.2f", fee3);
sub_vac2.setText(sub3);

String sub4 = String.format("%.2f", fee4);
sub_anti.setText(sub4);

String sub5 = String.format("%.2f", fee5);
sub_deworming.setText(sub5);

String sub6 = String.format("%.2f", fee6);
sub_cbc.setText(sub6);

String sub7 = String.format("%.2f", fee7);
sub_urine.setText(sub7);

String sub8 = String.format("%.2f", fee8);
sub_skin.setText(sub8);




subTotal = fee1 + fee2+ fee3+ fee4 + fee5 + fee6 + fee7 + fee8;
tax_ratefee = (subTotal * taxrate)/100;

//========================Tax=========================//
String subTax = String.format("%.2f", tax_ratefee);
txt_tax.setText(subTax);

//======================SubTotal======================//
String subTotalAll = String.format("%.2f", subTotal);
sub_total.setText(subTotalAll);

//====================OverallTotal=====================//

addup = subTotal + tax_ratefee;

String total = String.format("%.2f", addup);
txt_total.setText(total);


//=====================DateandTime=======================//

Calendar timer = Calendar.getInstance();
timer.getTime();
SimpleDateFormat intime = new SimpleDateFormat ("HH:mm:ss");
txt_time.setText(intime.format(timer.getTime()));

SimpleDateFormat indate = new SimpleDateFormat ("dd-MMM-yyyy");
txt_date.setText(indate.format(timer.getTime()));

我试过这样做：

if (qty_consult.getText().equals("")){
JOptionPane.showMessageDialog(null,"Empty Field/s");

}else  {
double Qty1 = Double.parseDouble(qty_consult.getText());
fee1 = Qty1 * price_consultfee;
String consult_fee = String.format("%.2f", price_consultfee);
price_consult.setText(consult_fee);

String sub1 = String.format("%.2f", fee1);
sub_consult.setText(sub1);

subTotal = fee1;
tax_ratefee = (subTotal * taxrate)/100;

//========================Tax=========================//
String subTax = String.format("%.2f", tax_ratefee);
txt_tax.setText(subTax);

//======================SubTotal======================//
String subTotalAll = String.format("%.2f", subTotal);
sub_total.setText(subTotalAll);

//====================OverallTotal=====================//

addup = subTotal + tax_ratefee;

String total = String.format("%.2f", addup);
txt_total.setText(total);


//=====================DateandTime=======================//

Calendar timer = Calendar.getInstance();
timer.getTime();
SimpleDateFormat intime = new SimpleDateFormat ("HH:mm:ss");
txt_time.setText(intime.format(timer.getTime()));

SimpleDateFormat indate = new SimpleDateFormat ("dd-MMM-yyyy");
txt_date.setText(indate.format(timer.getTime()));

并且它完美地计算了输入，并且在该错误之后再次弹出空字符串。我是不是做错了什么？

Answer 1

在处理用户输入时，您必须准备好期待任何事情，用户总是会找到破坏代码的方法，因此我建议您创建一种用于访问和解析输入的实用方法。例如：

private static double getNumberInput(JTextField field, double defaultValue){
String textInput = field.getText();
//Sorry, don't recall if getText can return a null value
//just making sure that we dont have a NullPointerException
//this part can be removed if getText never returns null
texInput = textInput == null? "" : textInput.trim(); //Make sure you trim the value
if("".equals(textInput)){
return defaultValue;
}
try{
return Double.parse(textInput);
}catch(NumberFormatException ex){
//Invalid input
return defaultValue;
}
}

通过这种方式，您可以重用该方法，并确保当您试图在字段中获取值时，您总是有一个值。

double Qty1 = getNumberInput(qty_consult, 0f);
double Qty2 = getNumberInput(qty_dogvac, 0f);
double Qty3 = getNumberInput(qty_catvac, 0f);

这样您就再也不会出现java.lang.NumberFormatException了。