如何在Java中检查用户输入是String，double还是long [英] How to check if user input is String, double or long in Java

问题描述

我是java的初学者。我想首先检查用户输入是String还是Double或int。如果是String，double或减号，则应提示用户再次输入有效的int号。只有当用户输入有效数字时，程序才会跳转尝试。我一直在想几个小时，我没有任何用处。请帮助，谢谢！

I'm a beginner in java. I want to check first if the user input is String or Double or int. If it's String, double or a minus number, the user should be prompted to enter a valid int number　again. Only when the user entered a valid number should then the program jump to try. I've been thinking for hours and I come up with nothing useful.Please help, thank you!

import java.util.InputMismatchException;
import java.util.Scanner;

public class Fizz {

public static void main(String[] args) {

    System.out.println("Please enter a number");

    Scanner scan = new Scanner(System.in);

    try {

        Integer i = scan.nextInt();

        if (i % 3 == 0 && (i % 5 == 0)) {
            System.out.println("FizzBuzz");
        } else if (i % 3 == 0) {
            System.out.println("Fizz");
        } else if (i % 5 == 0) {
            System.out.println("Buzz");
        } else {
            System.out.println(i + "は3と5の倍数ではありません。");
        }
    } catch (InputMismatchException e) {
        System.out.println("");

    } finally {
        scan.close();
    }

}

推荐答案

一个简单的解决方法是将整行/用户输入读取为String。
像这样的东西应该有效。 （未经测试的代码）：

One simple fix is to read the entire line / user input as a String. Something like this should work. (Untested code) :

   String s=null;
   boolean validInput=false; 
   do{
      s= scannerInstance.nextLine();
      if(s.matches("\\d+")){// checks if input only contains digits
       validInput=true;
      }
      else{
       // invalid input
     }
    }while(!validInput);

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