Java，使用多个条件语句的问题，while-loop，for-loop，if语句

Question

我正在做一个项目，帮助客人报名参加派对。

当事人必须存在于数据中

当然，想要的票的数量必须少于可用的票

我真的很难再添加一个条件——检查输入是否高于0。

我将整个for循环放入了另一个if语句中，正如您所看到的：if（ticketsWanted）

如果输入了低于1的内容，它会打印“请输入正数”

然而，它也打印了“这个派对不存在或者已经预订满了。”又来了...

基本上是在系统之后。出来println（“请输入正数”）；我希望程序提供一个选项，可以再次输入数字，直到它为正

以下是我的问题：

如何使用while循环，使其循环直到输入正数？

有没有更有效/更好的方法来做我打算做的事情？

谢谢你

 private static void signUp2(Guest validGuest){

              input.nextLine();
              System.out.println("Enter the name of the party");
              String partyName = input.nextLine();
              System.out.println("How many tickets the guest wishes to purchase?");
              int ticketsWanted = input.nextInt();
              boolean check = false;

              if(ticketsWanted > 0) {
               for(Party p: parties){
                 if(p.getPartyName().equals(partyName)){
                     if(ticketsWanted > e.getTickets()){
                 }
                   else{
                     check = true;  
                     validGuest.AddPartiesAndTickets(p, ticketsWanted);
                    }

                 }
              }
            }
             else{
                System.out.println("Please enter a positive number");

               }

            if(check == false){
            System.out.println("This party does not exist or is fully booked.");

Answer 1

 Using the continue keyword


   boolean check = false;
    boolean valid = false;

   while(valid == false){
   Sop( " how many tickets? ");
   ticketsWanted = input.nextInt ();
   if  (ticketsWanted < 0)  
       continue ;
   else   
    {
  valid = true;
// Rest of the code
 }

}

Answer 2

下面是一个非常简单的方法，当提示输入大于0的整数时，可以使用它确保用户输入正确的值。

  public static int getNumberGreaterThanZero(String prompt)
  {
      int number = 0;
      while(number == 0)
      {
          System.out.println(prompt);
          String inputFromUser = input.nextLine();
          //check if input matches any negative or positive number
          if(inputFromUser.matches("-\\d+|\\d+"))
          {
              number = Integer.parseInt(inputFromUser);
              if(number <= 0)
              {
                  System.out.println(number + " is not greater than 0");
                  number = 0; //have them try again
              }
          }
          else
              System.out.println("Error - " + inputFromUser + " is not a valid number");

      }
      return number;
  }

然后你可以像这样从你的其他方法调用它

          System.out.println("Enter the name of the party");
          String partyName = input.nextLine();
          int ticketsWanted = getNumberGreaterThanZero("How many tickets the guest wishes to purchase?");
          ...

Answer 3

添加以下方法：

int getNumberTickets() {
    System.out.println("How many tickets the guest wishes to purchase?");
    int ticketsWanted = input.nextInt();
    return(ticketsWanted);
}

并称之为使用：

int ticketsWanted = 0;
do {
    try {
       ticketsWanted = getNumberTickets();
       if (ticketsWanted < 1)
          throw new RuntimeException("Unused");
     catch(Throwable e) {
         ticketsWanted = -1;
         System.out.println("Invalid amount");
     }
while (ticketsWanted < 1);
 // now do your checks