为什么我不能将 String 转换为 char 并直接在 Switch 语句中使用？

Question

why cant i convert String to char & use in Switch Statement & if i left it as string the switch statement wont accept it either telling me it needs to be int or byte or short !!

public class Main {

    public static void main(String[] args) {
        String var1=getInput("enter first variable");
        String var2=getInput("enter second variable");
        String var3=getInput("enter opertaor");
        char c = var3.charAt(0);

        double d1=Double.parseDouble(var1);
        double d2=Double.parseDouble(var2);

        switch(c){
            case "+"://squiggly line appears & the bubble help says incompatible types
                System.out.println(d1+d2);
                break;
            case "-"://squiggly line appears & the bubble help says incompatible 
                System.out.println(d1-d2);
                break;
            case "*"://squiggly line appears & the bubble help says incompatible 
                System.out.println(d1*d2);
                break;
            case "/"://squiggly line appears & the bubble help says incompatible 
                System.out.println(d1/d2);
                break;
            default:
            System.out.println("Unrecognized operation");
            break;
        }
    }

    static String getInput(String prompt){
        System.out.println("prompt");
        Scanner sc=new Scanner(System.in);
        return sc.nextLine();
    }
}

Answer 1

You can use a String in case expressions, no need for a char . Change c like

String c = var3.substring(0, 1);

and your code would work. Alternatively, modify your case statements to use char . Like,

switch (c) {
case '+':
    System.out.println(d1 + d2);
    break;
case '-':
    System.out.println(d1 - d2);
    break;
case '*':
    System.out.println(d1 * d2);
    break;
case '/':
    System.out.println(d1 / d2);
    break;
default:
    System.out.println("Unrecognized operation");
    break;
}

Answer 2

You can use a char literal instead:

  switch(c){
      case '+':
          System.out.println(d1+d2);
          break;
...

The types are different so you can't directly compare them. They happen to be convertible in this particular case, but that's not true in general, so the compiler can't allow that.

Answer 3

Try out below code and it will execute

public static void main(String[] args) {
    String var1 = getInput("enter first variable");
    String var2 = getInput("enter second variable");
    String var3 = getInput("enter opertaor");
    char c = var3.charAt(0);

    double d1 = Double.parseDouble(var1);
    double d2 = Double.parseDouble(var2);

    switch (c) {
        case '+':
            System.out.println(d1 + d2);
            break;
        case '-':
            System.out.println(d1 - d2);
            break;
        case '*': 
            System.out.println(d1 * d2);
            break;
        case '/': 
            System.out.println(d1 / d2);
            break;
        default:
            System.out.println("Unrecognized operation");
            break;
    }

}

static String getInput(String prompt) {
    System.out.println("prompt");
    Scanner sc = new Scanner(System.in);
    return sc.nextLine();

}

Change case '+': instead of comparing String case "+": Also Check your Java version, From JDK v1.7 will allow you to use Strings in switch statement as what you did in your code snippet. Let me know if you are looking for another solution

Answer 4

You cant parse a String into a char because a String is to big to fit. Think of it like a String consist of multiple chars, so its just like a char array in one piece.