switch expressions - java 17

[Tim Bant]

Hi there, I've been taking some mock questions re Java 17.

I noticed this snippet:

switch(x){
case 2 -> {
    System.out.print("A");
    break; //redundant but allowed
   }
case 3 -> System.out.print("B");
     //break; //break not allowed here
    default -> System.out.print("C"); //default is not necessary in a switch statement
}

Where it says //redundant but allowed, shouldn't there be a yield statement since its using {} ? Or is it that because it isn't returning a value, this is permitted?

Thanks

[Mike Simmons]

Right, if it were "returning" a value, it would have to use yield.  Since it's not, break is fine (though pointless here).

[Tim Bant]

Cheers - I wonder if this could be one of those, however, whereby they changed the constraint slightly in later versions, for example, this page here (https://docs.oracle.com/en/java/javase/17/language/switch-expressions-and-statements.html#GUID-BA4F63E3-4823-43C6-A5F3-BAA4A2EF3ADC) under Exhaustiveness, you'll see it says it must have a yield when using {}

[Mike Simmons]

No, we're mixing up switch statements and switch expressions.  Your first example was actually a switch statement, with no "return" values.  There, break is fine, and yield does not work.  When I said "if  it were 'returning' a value", I was actually talking about switch expressions.  This is also what they're talking about in the documentation you're now looking at.  Once you place a switch in a context where it's expected to have a value (e.g., putting it to the right of an equals sign, or as part of a larger expression) then the rules for switch expressions kick in, and break is no longer allowed, only yield.

[Tim Bant]

Makes sense, thanks for clarifying for me!

[Jhonson Fernando]

Differences Between the Switch Statement and Switch Expression

- Expression Result: The switch statement does not return a value, while the switch expression returns a value.
- Syntax: The switch statement uses the colon (`:`) notation, while the switch expression uses the arrow (`->`) notation.
- `break` Statement: The `break` statement is required in each `case` block in the switch statement, while it is optional in the switch expression.
- `default` Block: The `default` block is required in the switch statement, while it is optional in the switch expression.
- Fall-Through: Fall-through is not allowed in the switch expression, while it is allowed in the switch statement.
- Multiple Constants: Multiple `case` constants can be in a single `case` label in the switch statement, while the switch expression does not allow this.
- Data Types: The switch statement allows primitive data types, wrapper classes, Enums, and Strings as `selector_expression`, while the switch expression only supports Enums and Strings.
- Scope: The variables defined in each `case` block in the switch expression are scoped to that block only, while they are accessible in the entire `switch` statement in the switch statement.

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