如何在java中结束if语句？

Question

我是java的初学者，我正在研究华氏和摄氏转换器之间的问题。但是，如果有人选择第一个选项，那么当该代码运行时，第二个选项将自动运行，如下所示。我究竟做错了什么？

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。你在他们真正开始之前就结束了，所以所有的代码都会运行。

在Java中，括号应紧跟在右括号之后。 （后该生产线还直接后计数）

代码应该是这样的：

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

变化的if语句：

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."); 
     }  
    } 

}