如何在java中結束if語句？

Question

我是java的初學者，我正在研究華氏和攝氏轉換器之間的問題。但是，如果有人選擇第一個選項，那麼當該代碼運行時，第二個選項將自動運行，如下所示。我究竟做錯了什麼？

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

刪除if語句後面的分號。你在他們真正開始之前就結束了，所以所有的代碼都會運行。

在Java中，括號應緊跟在右括號之後。 （後該生產線還直接後計數）

代碼應該是這樣的：

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 2

變化的if語句：

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."); 
     } 
     else 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."); 
     }  
    } 

}