Lambda expresions and "? :" operator in Java 14

Question

Good day to everyone,

I have a question regarding the usage of the ? : operator in the lambda expressions, especially in the switch statements. Could you kindly clarify, why the below code would not work and will be marked as Not a statement

 switch (separatedTransaction[0]) {
            case "u" -> processUpdate(Integer.parseInt(separatedTransaction[1]), Integer.parseInt(separatedTransaction[2]), separatedTransaction[3]);
            case "o" -> processOrder(separatedTransaction[1], Integer.parseInt(separatedTransaction[2]));
            case "q" -> separatedTransaction.length > 2 ? processQuery(Integer.parseInt(separatedTransaction[2])):processQuery(separatedTransaction[1]);
            default -> System.out.println("Invalid transaction");
        }

And the next one will.

 switch (separatedTransaction[0]) {
            case "u" -> processUpdate(Integer.parseInt(separatedTransaction[1]), Integer.parseInt(separatedTransaction[2]), separatedTransaction[3]);
            case "o" -> processOrder(separatedTransaction[1], Integer.parseInt(separatedTransaction[2]));
            case "q" -> {
                if (separatedTransaction.length > 2) {
                    processQuery(Integer.parseInt(separatedTransaction[2]));
                } else {
                    processQuery(separatedTransaction[1]);
                }
            }
            default -> System.out.println("Invalid transaction");
        }

Is there a way to use the ? : operator in the lambda expressions at all?
If so, could you kindly provide some code examples.

`processQuery()` must have a non void return type in order to be used as the 2nd or 3rd operands of the ternary conditional expression. — Eran, Sep 22 '20 at 13:26
https://stackoverflow.com/questions/9450864/java-ternary-with-no-return-for-method-calling — Federico klez Culloca, Sep 22 '20 at 13:30
BTW, there are no lambda expressions in the code you posted. — Eran, Sep 22 '20 at 13:30
Use `if-else` if you are calling `void` methods on operands. — Raj, Sep 22 '20 at 13:32
Thanks guys for the clarification, this was the answer I've searched for. Non-void return methods should be used in the ternary expressions. — ThePrettyFace, Sep 22 '20 at 13:32
The ternary operator returns a value, which doesn't work with that switch statement. — NomadMaker, Sep 22 '20 at 13:57

score 1 · Accepted Answer · answered Sep 22 '20 at 13:33

Forget about all the jazz of that switch statement, it's a red herring; completely irrelevant to the situation (and as a side note, those -> arrows aren't 'lambdas'. They're just part of switch-as-expression syntax).

Just this:

separatedTransaction.length > 2 ? processQuery(Integer.parseInt(separatedTransaction[2])):processQuery(separatedTransaction[1])

explains the failure. That is invalid java code. And wrapping it in a new feature introduced in java14 isn't going to make it any more legal.

The ternary operator construct takes the following form:

booleanExpression ? expr1 : expr2

where expr1 and expr2 must themselves be expressions. The type of the whole thing is the common ground between the type of expr1 and expr2, and, crucially, that common ground must not be void.

That's the problem: processQuery returns void and therefore cannot be used in any of the 3 'slots' in a ternary expression.

Lambda expresions and "? :" operator in Java 14

1 Answers1