How to set an empty or not empty entry for a switch case statement?-CodePudding

I'd like to know to set an entry to validate if a String is empty or not empty in a switch-case statement. Let me show you:

String str = 'value'
switch(str){
    case str == '':
        println('Entered an empty value')
        break
    case str != '':
        println('Entered value ' str)
        break
    case 'CoDe':
        println('Entered special code ' str)
        break
    default:
        println('Incorrect entry')
        break
}

I know how to set an entry with a value (case 3) but I don't know how to set a entry with an empty or not empty string value.

Any help?

CodePudding user response：

As commented, what you need in Java is a series of if tests.

In the String class, you can test either:

The string has no characters at all (isBlank)
The string has no characters OR has only whitespace characters (isEmpty)

if ( str.isEmpty() ) { System.out.println( "ERROR - String has no characters." ); }
else if ( str.isBlank() ) { System.out.println( "ERROR - String has only whitespace." ); }
else if ( str.equals( "CoDe" ) ) { System.out.println( "Code received." ); }
else { System.out.println( "ERROR - Incorrect entry." ); }

See that code run live at Ideone.com.

Before that code block, I would add a null-check.

Objects.requireNonNull( str ); // Throw exception if null.

I find the if - else if - else construct in Java to be awkward in terms of readability. The switch syntax is much better at making obvious that a series of possibilities is being tested, mutually-exclusive, with a single result.

I do wish Java offered a cascading test for a series of boolean expressions. I have used such a feature in another language. There I found the cascading-boolean-tests to be quite practical for handling a series of business rules. But, alas, no such feature in Java. If only Brian Goetz were taking my calls.

I do not know Groovy. Perhaps Groovy provides another facility.

CodePudding user response：

I tested it, and I think I have the answer for you.

switch(str){
    case "": // empty
        println("Entered an empty value")
        break
    case "CoDe": // str == CoDe
        println("Entered special code " str)
        break
    default: // String not empty and not "CoDe"
        println("Not empty")
        break
}

It works because you have case "" which is the empty string. Meaning that everithing else is not empty. everything else is the default:

If you are not convinced, I'll give you a different example with the same meaning.

if(str.isEmpty()) {
   // do something
} else if(!str.isEmpty()) { // <- this if is redundant
   // do something else
}

You don't need the second if, because, you enter the else brench only if str is not empty! I appleid the same logic to the case. And it works because case "": in Java is valid.