java 常量表达式,需要常量表达式？ （Java switch语句）[通俗易懂]

大家好，又见面了，我是你们的朋友全栈君。

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);

}

}

It throws a “Constant expression required” error when it’s compiled and it points to the case p: line, however, it also throws it for f: if I switch them so I must be doing something completely off.

解决方案

Yes, a case expression has to be a constant (or an enum constant name) – you can’t use a variable. See the Java Language Specification section 14.11 (switch statements) for more details. (You hadn’t even initialized the variables, so it’s not clear what you expected to happen, to be honest.)

Did you mean:

case ‘p’:

…

case ‘f’:

…

? This will match your input (type) against the character literals ‘p’ and ‘f’.

(As an aside, if this stumped your teacher, I have concerns about how suitable they are to be teaching Java. This is reasonably basic stuff.)

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