java - 二元运算符 "-"第一个类型 : int; second type: java. lang.String 的错误操作数类型

Question

我在将 String(birthyear) 转换为 int(age) 时遇到问题。我希望有人输入他们的出生年份，然后让程序进行简单的减法计算来计算出他们的年龄。我是编程新手，所以我一直在四处寻找，大多数地方都告诉我同样的事情。

Integer.parseInt(birthyear);

但是，完成此操作后，当我尝试进行数学计算时......

int age = year-birthyear;

我在标题中发现了错误。

public class WordGameScanner
{
    public static void main(String[] argus)
    {
        String name;
        String home;
        String birthyear;
        String course;
        String reason;
        String feedback;
        int year = 2013;

        Scanner input = new Scanner(System.in);
        System.out.print("What is your name: ");
        name = input.nextLine();
        System.out.print("Where are you from: ");
        home = input.nextLine();
        System.out.print("What year were you born: ");
        birthyear = input.nextLine();
        Integer.parseInt(birthyear);
        System.out.print("What are you studying: ");
        course = input.nextLine();
        System.out.print("Why are you studying " + course + ": ");
        reason = input.nextLine();
        System.out.print("How is " + course + " coming along so far: ");
        feedback = input.nextLine();

        int age = year-birthyear;

        System.out.println("There once was a person named " + name +
            " who came all the way from " + home +
            " to study for the " + course +
            " degree at --------------.\n\n" + name +
            " was born in " + birthyear + " and so will turn " + age +
            " this year.");
        System.out.println(name + " decided to study the unit ------------, because \"" +
            reason + "\". So far, ----------- is turning out to be " +
            feedback + ".");
    }
}

如果发错地方了，我很抱歉，这只是我的第二篇文章。我只是点击“提问”并按照说明操作>。<

Answer 1

int age = year-Integer.parseInt(birthyear);

调用parseInt不会将变量StringbirthYear重新定义为int，它只是返回一个int您可以将其存储在另一个变量中的值(例如 intbirthYearInt = Integer.parseInt(birthYear);)或在上述表达式中使用。

<小时/>

您可能还需要花一点时间考虑一下输入。

您的用户可能只输入最后两位数字(“83”而不是“1983”)，因此您可以执行以下操作:

int birthYearInt = Integer.parseInt(birthYear);
if (birthYear.length() == 2) {
  // One way to adjust 2-digit year to 1900.
  // Problem: There might not be more users born in 1900 than born in 2000.
  birthYearInt = birthYearInt + 1900; 
}
int age = year = birthYearInt;

或者，您可以使用 java.text.NumberFormat正确处理输入中的逗号。 NumberFormat 是处理人类数字的好方法，因为它处理人类数字格式的方式与计算机不同。

<小时/>

另一个问题是，它使用中国的年龄计数系统，每个人的年龄在新年(中国农历，而不是公历)都会加一。但这并不是世界范围内计算年龄的方式。例如，在美国和欧洲大部分地区，您的年龄会在生日周年纪念日增加。