验证：确保字符串是数字

Question

我正在为我的课程作业编写代码，我需要验证方面的帮助。我想确保输入的字符串是一个数字。 我的老师给了我一段代码，用 try and catch，它确实有效，但它有一个我不知道如何解决的问题。

因此，如果有人可以通过告诉我此代码有什么问题来帮助我，我将不胜感激，或者如果有人可以给我另一个简单的代码来验证数据以确保它是一个数字。

boolean StartTimeIsANumber; // BOOLEAN CREATED
  StartTimeIsANumber = false; // BOOLEAN SET TO FALSE
  double starttime=0; // VARIBALE IS INITIALISED

  System.out.println("Please enter the start time in seconds"); // asks for time in seconds

  while(StartTimeIsANumber==false) // WHILE OK IS FALSE
   {
    try {

     String input; // start time is stored as a string
     input = kb.next(); // reads the start time in as a string
     starttime = Double.parseDouble(input); // converts to double
     System.out.println("start time: "+starttime); // outputs the start time
     StartTimeIsANumber =true; // if its a number boolean set will convert to true and will break out of the loop
     }  catch (NumberFormatException e) {
      // TODO Auto-generated catch block
      // e.printStackTrace(); (this is the line that makes red writing, commenting it out stops red writing)
      System.out.println("start time must be a number"); // further 'advice'
              }

   }

我有一张它的作用的图片，见下文。我写的字数就是它输出'start time must be a number'的次数！

Answer 1

它会迭代该行的每个单词。您必须将整个输入行视为一个语句。

boolean StartTimeIsANumber = false; 
double starttime=0; // VARIBALE IS INITIALISED
String input = "";

System.out.println("Please enter the start time in seconds");

while(StartTimeIsANumber == false) {
    try {
        while (kb.hasNext()) {
            input += (kb.next() + " ");  
        }
        // or input = kb.nextLine();

        starttime = Double.parseDouble(input);
        System.out.println("start time: " + starttime);
        StartTimeIsANumber = true;
    }  catch (NumberFormatException e) {
        System.out.println("start time must be a number");
    }
}