Java：尝试使用 while 循环检查扫描仪输入的 int 变量，不确定如何初始化变量？

Question

这是我自己编写的第一批程序之一。我正在编写一个程序来告诉你你的星座是什么，我让程序使用我导入的扫描仪方法运行，但我遇到的问题是现在我正在尝试使用检查用户输入一个 while 循环，它没有按我的预期运行，当我编译我的代码时，我遇到的错误是我的 int 类型的变量没有被初始化。我在声明它时没有指定值时写了它，我不确定我应该为它指定什么来解决这个问题。

导入java.util.Scanner；

公开课 MyStarSign {

public static void main(String[] args) {

Scanner myScanner = new Scanner(System.in);  // Create a Scanner object
System.out.println("What month were you born?");

String birthMonth = "";

    

birthMonth= myScanner.next();  // Read user input



System.out.println("You were born in " + birthMonth + "?");  // Output user input

System.out.println("What day of the month were you born?");

int birthDay;

    while (birthDay > 31) {

        System.out.println("Please enter a valid day of the month");

        birthDay = myScanner.nextInt();
    
    }

这就是我的代码现在的样子 ^^

现在我尝试的解决方案：

int 生日 = myScanner.nextInt();

    while (birthDay > 31) {

        System.out.println("Please enter a valid day of the month");

        birthDay = myScanner.nextInt();
    
    }

这就是我试图解决的问题，尽管我在编译代码时再次遇到同样的问题

Answer 1

public static void main(String[] args) {

    Scanner myScanner = new Scanner(System.in);  // Create a Scanner object
    System.out.println("What month were you born?");

    String birthMonth = "";

    birthMonth= myScanner.next();  // Read user input

    System.out.println("You were born in " + birthMonth + "?");  // Output user input
    System.out.println("What day of the month were you born?");

    int birthDay;
    birthDay = myScanner.nextInt();

    while (birthDay > 31) {
        System.out.println("Please enter a valid day of the month");
        birthDay = myScanner.nextInt();
    }
}

Answer 2

Initialize 表示它需要有一个初始值，像这样：

int birthDay = 0;

所以你唯一需要做的就是为你的变量添加一个值

编辑：试试这个代码

import java.util.Scanner;

public class MyStarSign 
{

    public static void main(String[] args) 
    {

        Scanner myScanner = new Scanner(System.in);  // Create a Scanner object
        System.out.println("What month were you born?");

        String birthMonth = "";

        birthMonth= myScanner.next();  // Read user input

        System.out.println("You were born in " + birthMonth + "?");  // Output user input

        System.out.println("What day of the month were you born?");

        int birthDay = 0;

        while (birthDay > 31) 
        {

            System.out.println("Please enter a valid day of the month");

            birthDay = myScanner.nextInt();

        }
    }
}