如果我在输出端输入字母，java程序会崩溃，请帮助解决这个问题

Question

如果我输入字母，下面的程序不应该崩溃（错误粘贴在底部）；相反，它应该要求用户输入一个有效的数字。

import java.text.NumberFormat;
import java.util.Scanner;

public class Main {

public static void main(String[] args) {
    final byte MONTHS_IN_YEAR = 12;
    final byte PERCENT = 100;
    int principal = 0;
    float monthlyInterest = 0;
    int numberOfPayments = 0;

    Scanner scanner = new Scanner(System.in);
    System.out.println("Enter a number between 1,000 and 1,000,000.");

    while(true) {
        System.out.print("Principal: ");
         principal = scanner.nextInt();
        if (principal >= 1000 && principal <= 1000_000)
            break;
        System.out.println("Enter a valid input");
    }

    while(true) {
        System.out.print("Annual Interest Rate: ");
        float annualInterest = scanner.nextFloat();
        if (annualInterest > 0 && annualInterest <= 15) {
            monthlyInterest = annualInterest / PERCENT / MONTHS_IN_YEAR;
            break;
        }
        System.out.println("Enter a value between 1 and 15");
    }

    while(true) {
        System.out.print("Period (Years): ");
        byte years = scanner.nextByte();
        if (years > 0 && years <= 30) {
            numberOfPayments = years * MONTHS_IN_YEAR;
            break;
        }
        System.out.println("Enter a value between 1 and 30");
    }

    double mortgage = principal * (monthlyInterest * Math.pow(1 + monthlyInterest, numberOfPayments))
            / (Math.pow(1 + monthlyInterest, numberOfPayments) - 1);

    String mortgageFormatted = NumberFormat.getCurrencyInstance().format(mortgage);
    System.out.println("Mortgage: " + mortgageFormatted);



}
}

**输出#1//当用户输入时，句号为abc

Enter a number between 1,000 and 1,000,000.
Principal: 600
Enter a valid input
Principal: 2000
Annual Interest Rate: 0
Enter a value between 1 and 15
Annual Interest Rate: 3.5
Period (Years): abc
Exception in thread "main" java.util.InputMismatchException
at java.base/java.util.Scanner.throwFor(Scanner.java:939)
at java.base/java.util.Scanner.next(Scanner.java:1594)
at java.base/java.util.Scanner.nextByte(Scanner.java:2002)
at java.base/java.util.Scanner.nextByte(Scanner.java:1956)
at com.company.Main.main(Main.java:39)

Process finished with exit code 1

输出#2//当年份数据类型为字节，但用户输入300，而不是崩溃时，程序应要求用户输入有效数字

Enter a number between 1,000 and 1,000,000.
Principal: 1000000
Annual Interest Rate: 3.9
Period (Years): 300
Exception in thread "main" java.util.InputMismatchException: Value out of range. Value:"300" 
Radix:10
at java.base/java.util.Scanner.nextByte(Scanner.java:2008)
at java.base/java.util.Scanner.nextByte(Scanner.java:1956)
at com.company.Main.main(Main.java:39)

Process finished with exit code 1

Answer 1

您应该使用try Catch，如下所示：

while(true) {
    System.out.print("Period (Years): ");
    try{
       byte years = scanner.nextByte();
       if (years > 0 && years <= 30) {
        numberOfPayments = years * MONTHS_IN_YEAR;
        break;
       }
       System.out.println("Enter a value between 1 and 30");
    catch (Exception e){
      System.out.println("Value must be numeric");
    }
}