错误：找不到符号int r = in.read（）;

Question

error: cannot find symbol
     int r=in.read();      
           ^
symbol:   variable in
location: class Demo1
1 error

import java.lang.*;  

class Demo1 {  
    public static void main (String arg[]) throws Exception{ 
        int r = in.read();
        char ch = (char)r; 
        float f = (float) ch; 
        System.out.println(f);
    }
}