switch语句如何在带有字符串参数的Java 1.5中工作？

Question

Can i implement switch statements(by passing string arguments) in java 5 without making use of enums?I tried doing it using hashcode but i got an error

package com.list;

import java.util.Scanner;

public class SwitchDays implements Days {

    static final int str = "sunday".hashCode();




    public static void main(String[] args) {


          Scanner in=new Scanner(System.in);    
            String day= in.nextLine();

        switch (day.hashCode()) {

        case str:
            System.out.println(day);

            break;

        default:
            break;
        }
            }


}

str in case str given an error:

case expressions must be constant expressions

Please guide.

Answer 1

The problem is that str is referring to the expression "sunday".hashCode() , which is not a compile time constant expression as described by the JLS:

A constant expression is an expression denoting a value of primitive type or a String that does not complete abruptly and is composed using only the following: ... Qualified names (§6.5.6.2) of the form TypeName . Identifier that refer to constant variables (§4.12.4).

When you check the definition of constant variables:

A constant variable is a final variable of primitive type or type String that is initialized with a constant expression (§15.28). Whether a variable is a constant variable or not may have implications with respect to class initialization (§12.4.1), binary compatibility (§13.1, §13.4.9), and definite assignment (§16 (Definite Assignment)).

Since "sunday".hashCode() does not meet this requirements, you get the error.

If you would change "sunday".hashCode() to a real compile time constant like 3 it would compile.

Answer 2

The most straight forward solution is to make an enum, ie.

enum Days{
    sunday, monday;
}

Then it could be used as:

Day d = Day.valueOf("sunday");
switch(d){
    case sunday:
        System.out.println("ONE");
        break;
    case monday:
        System.out.println("TWO");
        break;
}