SWITCH语句不工作 - Java

Question

我正在制作一个程序来计算通过某种材料的声音的速度。这里是代码：

switch (user_Choice) 
{ 
case 1: 
    System.out.println("The sound wave took " + speed.getSpeedInAir() + " seconds to travel through " + 
        distance + " feet of Air."); 
    break; 

case 2: 
    System.out.println("The sound wave took " + speed.getSpeedInWater() + " seconds to travel through " + 
        distance + " feet of Water."); 
    break; 

case 3: 
    System.out.println("The sound wave took " + speed.getSpeedInSteel() + " seconds to travel through " + 
        distance + " feet of Steel."); 
    break; 

default: 
    System.out.println("Not a valid input.");} 

我不知道为什么这不起作用。每个案例我可以没有那么多“+”号？

编辑：这里是输入USER_CHOICE

System.out.println("Pick a medium (1, 2, or 3):\n1. Air\n2. Water\n3. Steel"); 
user_Choice = kbReader.nextInt(); 
System.out.print("Enter the distance the sound wave traveled in feet: "); 
distance = kbReader.nextDouble(); 
SpeedOfSound speed = new SpeedOfSound(distance); 

Answer 1

如果kbReader是Scanner记得nextInt()和nextDouble()需要nextLine()in order to get rid of the \n。在nextInt()之后调用nextDouble()将给出distance值null。

一种解决方法是第一个nextInt()后添加nextLine()：

System.out.println("Pick a medium (1, 2, or 3):\n1. Air\n2. Water\n3. Steel"); 
user_Choice = kbReader.nextInt(); 
kbReader.nextLine(); //Consumes the \n (new line) character. 
System.out.print("Enter the distance the sound wave traveled in feet: "); 
distance = kbReader.nextDouble(); 
SpeedOfSound speed = new SpeedOfSound(distance); 

如果在你user_Choice = kbReader.nextInt();您正在执行另一个nextInt()或相近，switch总是会选择默认值，因为user_Choice是null。