Question

如果用户输入的电子邮件地址中不包含“ @”符号，则必须使用if / else语句退出程序。这是我这部分的代码：

=QUERY({
 IFERROR('1'!A2:C,  {"","",""});
 IFERROR('2'!A2:C,  {"","",""});
 IFERROR('3'!A2:C,  {"","",""});
 IFERROR('4'!A2:C,  {"","",""});
 IFERROR('5'!A2:C,  {"","",""});
 IFERROR('6'!A2:C,  {"","",""});
 IFERROR('7'!A2:C,  {"","",""});
 IFERROR('8'!A2:C,  {"","",""});
 IFERROR('9'!A2:C,  {"","",""});
 IFERROR('10'!A2:C, {"","",""});
 IFERROR('11'!A2:C, {"","",""});
 IFERROR('12'!A2:C, {"","",""});
 IFERROR('13'!A2:C, {"","",""});
 IFERROR('14'!A2:C, {"","",""});
 IFERROR('15'!A2:C, {"","",""});
 IFERROR('16'!A2:C, {"","",""});
 IFERROR('17'!A2:C, {"","",""});
 IFERROR('18'!A2:C, {"","",""});
 IFERROR('19'!A2:C, {"","",""});
 IFERROR('20'!A2:C, {"","",""})}, 
 "select Col1,sum(Col3) 
  where Col1 is not null 
  group by Col1 
  order by sum(Col3) desc 
  label sum(Col3)''")

错误：

//prompt user for their email address

System.out.print("\nPlease enter your email address: ");

//read user's input
emailAddress = keyboard.next();

//create username
String username = emailAddress.substring(0, emailAddress.indexOf('@'));

 //create username
atSign = emailAddress.lastIndexOf("@");
if(atSign >= 0){
    username = emailAddress.substring(0, atSign);
}
else{
    System.out.print("You've entered an invalid email address!");
    System.out.println("Goodbye!");
}

Answer 1

问题出在您的电话上

String username = emailAddress.substring(0,emailAddress.indexOf('@'));

如果电子邮件地址中不包含“ @”，则emailAddress.indexOf('@')返回-1，表示您正在尝试呼叫emailAddress.substring(0, -1)。

-1是无效索引，导致StringIndexOutOfBoundsException。

Answer 2

String username = emailAddress.substring(0, emailAddress.indexOf('@'));//this will throw exception

该怎么办？

之前创建username，并将其设置为null或空字符串。然后检查该符号是否存在。

 String username = null;
 // or String username = "";

     //create username 
 atSign = emailAddress.lastIndexOf("@"); 
  if(atSign >= 0){ 
    username = emailAddress.substring(0, atSign);
 } 
 else{ 
     System.out.print("You've entered an invalid email address!");
     System.out.println("Goodbye!");


   // use return to stop code here if in a method(better choice) or
   // if in the main() uncomment the code below
   // System.exit(0);
 }

如果未检测到“ @”符号，则会在屏幕上显示错误消息

2 个答案: