验证倍数输入

Question

我不希望用户输入负值。如何检测负值以及InputMismatchException？这是我到目前为止的代码！代码似乎不正常，无法找出问题所在。我想验证用户输入以确保负数，字符串和双精度无效并提示用户输入正确的数字，该数字应为正整数。

            do {
                try {
                    System.out.println("How many " + teaName + " did you today?");
                    if(input.hasNextInt() && (numberItem = input.nextInt()) > 0) {
                        istrue = false;

                        numberItem = input.nextInt();

                    }

                } catch (InputMismatchException e) {
                    input.nextLine();
                    System.out.println("Please enter right number");
                    istrue = true;
                }
                catch (NoSuchElementException e){
                    System.out.println(" Please enter positive integers");
                }
            } while (istrue);

Answer 1

         do {
            try {
                System.out.println("How many " + teaName + " did you today?");
                if(input.hasNextInt()) {
                    if (numberItem = input.nextInt()) > 0) {
                        istrue = false;

                        numberItem = input.nextInt();
                    } else {
                        throw new InputMisMatchException("negative num");
                    }

                }

            } catch (InputMismatchException e) {
                input.nextLine();
                System.out.println("Please enter right number");
                istrue = true;
            }
            catch (NoSuchElementException e){
                System.out.println(" Please enter positive integers");
            }
        }while (istrue);

这应该可行，我所做的就是在数字为负数时抛出一个InputMismatchException。