java - java中如何结束if语句？

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已关闭。这个问题是 not reproducible or was caused by typos 。目前不接受答案。

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已关闭 7 年前。

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我是java初学者，正在解决华氏度和摄氏度之间转换器的问题。但是，如果有人选择第一个选项，则当该代码运行时，第二个选项会自动运行，如下所示。我做错了什么？

import java.util.Scanner;

public class FahrenheittoCelsius {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        System.out.println("If you would like to convert a temperature from Fahrenheit to Celcius, enter 1.");
        System.out.println("If you would like to convert a temperature from Celcius to Fahrenheit, enter 2.");
        int mode = scan.nextInt();
        if (mode == 1);
        {   
            System.out.println("Enter the temperature in Fahrenheit");
            int Ftemp = scan.nextInt();
            int Cnewtemp = (Ftemp - 32) * 5 / 9;
            System.out.println("The temperature in Celcius is " + Cnewtemp + " degrees.");
        }
        if (mode == 2);
        {   
            System.out.println("Enter the temperature in Celcius");
            int Ctemp = scan.nextInt();
            int Fnewtemp = Ctemp * 9 / 5 + 32;
            System.out.println("The temperature in Fahrenheit is " + Fnewtemp + " degrees.");   
        }       
    }

}

Answer 1

删除 if 语句后面的分号。您在它们实际开始之前结束它们，因此所有代码都会运行。

在 Java 中，括号应紧跟在右括号之后。 (之后的行也算作紧接在之后的行)

代码应如下所示:

import java.util.Scanner;

public class FahrenheittoCelsius {

  public static void main(String[] args) {
      Scanner scan = new Scanner(System.in);
      System.out.println("If you would like to convert a temperature from Fahrenheit to Celcius, enter 1.");
      System.out.println("If you would like to convert a temperature from Celcius to Fahrenheit, enter 2.");
      int mode = scan.nextInt();
      if (mode == 1)
      {   
          System.out.println("Enter the temperature in Fahrenheit");
          int Ftemp = scan.nextInt();
          int Cnewtemp = (Ftemp - 32) * 5 / 9;
          System.out.println("The temperature in Celcius is " + Cnewtemp + " degrees.");
       }
      if (mode == 2)
      {   
          System.out.println("Enter the temperature in Celcius");
          int Ctemp = scan.nextInt();
          int Fnewtemp = Ctemp * 9 / 5 + 32;
          System.out.println("The temperature in Fahrenheit is " + Fnewtemp + " degrees.");   
      }       
  }

}