需要常量表达式吗?(Java switch 语句)

I have no idea what is causing this error. My teacher and I went over it and couldn't find what was wrong.

import java.util.Scanner;
public class MailAssignment
{
public static void main(String [] args){

    Scanner userinput = new Scanner(System.in);
    char p;
    char f;
    double price = 0;
    System.out.println("First class or priority?");
    char type = userinput.next().charAt(0);
    System.out.println("How much does the package weigh? (in ounces)");
    double weight = userinput.nextDouble();

    switch (type){
     case p:
     if (weight > 16)
        price = weight * 3.95;

        else if (weight > 32) 
            price = (1.20 * (weight / 16));
       else
            price = 3.50 * weight;


        break;


     case f: 
     if (weight < 1 )
     price = 0.34;

     else if ( weight > 1)
     price = 0.34 + (weight * 21);

     else if (weight > 13)
     price = weight * 3.95;

        else if (weight > 32) 
            price = 1.20 * (weight / 16);
        else
            price = 3.50 * weight;

            break;

        }     

    System.out.println("Your price is: " +price);
    }
}

它在编译时抛出需要常量表达式"错误，它指向 case p: 行，但是，如果我切换它们，它也会为 f: 抛出它，所以我必须完全关闭.

case 'p':
    ...

case 'f':
    ...