Can you refer to case values inside the code block of the switch statement?

Question

So can you do something like this in Java:

Can you get the value being switched on inside a switch expression

I have quite a few cases in my code which look like this (actual logic code removed for clarity reasons):

    switch (weatherSystem.getRealClass().getSimpleName())
    {
        case "SyncWeatherSystem":
            logger.info("initializing sync weather system");
            …
            break;
        case "AsyncWeatherSystem":
            logger.info("initializing  async weather system");
            …       
            break;
        case "FixedWeatherSystem":
            logger.info("initializing fixed weather system");
            …
            break;
        case "NoWeatherSystem":
            logger.info("initializing no weather system");
            …
            break;
    }

And I really would love to do like:

    switch (weatherSystem.getRealClass().getSimpleName())
    {
        case "SyncWeatherSystem":
            logger.info("initializing {}", case.value);
            …
            break;
        case "AsyncWeatherSystem":
            logger.info("initializing {}", case.value); 
            …
            break;
        case "FixedWeatherSystem":
            logger.info("initializing {}", case.value);
            …
            break;
        case "NoWeatherSystem":
            logger.info("initializing {}", case.value);
            …
            break;
    }

Is this possible in Java?

You don't need the switch at all - just use string concatenation "directly." — EJoshuaS - Stand with Ukraine
– EJoshuaS - Stand with Ukraine, Commented Mar 19, 2022 at 19:22
@EJoshuaS-StandwithUkraine Only if default isn't a no-op. — Elliott Frisch
– Elliott Frisch, Commented Mar 19, 2022 at 19:23
Why do you need an alternative way to get the value, instead of using the same expression as in the switch parentheses? If it takes time to generate and return the value, store it in a variable (perhaps a final one) before using it in a switch. — Lev M.
– Lev M., Commented Mar 19, 2022 at 19:40

Elliott Frisch · Accepted Answer · 2022-03-20 16:23:55Z

4

No. It is not. But, weatherSystem.getRealClass().getSimpleName() is. I suggest you save that value to a local variable. And all your case(s) seem to do the same thing. So, as posted, you could simplify it. Like

String sName = weatherSystem.getRealClass().getSimpleName();
switch (sName)
{
    case "SyncWeatherSystem":
    case "AsyncWeatherSystem":
    case "FixedWeatherSystem":
    case "NoWeatherSystem":
        logger.info("initializing {}", sName);
        break;
}

edited Mar 20, 2022 at 16:23

answered Mar 19, 2022 at 19:22

Elliott Frisch

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5 Comments

Basil Bourque Over a year ago

Good Answer. I suggest being more explicit about the main change being the move of the call to getSimpleName to a named local variable. I had to look a few times to see what you did. Perhaps you should just show that first, before separately showing the collapsed case cascade.

Snorik Over a year ago

I am sorry - the actual logic code is actually removed, there is code between logger.info and break;

Basil Bourque Over a year ago

@Snorik In the future, I suggest you show additional but irrelevant code by adding a line with a single character, ellipsis ….

Snorik Over a year ago

@BasilBourque thank you for the reminder. Just added [...] to make it clear

Basil Bourque Over a year ago

@Snorik I altered your edit to use the actual ellipsis character ( Option + Semicolon on macOS), and to move indented with your code.

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