Java 8 Lambda Expression

Question

I am new learner for Java 8 lambda . I found a statement in a book (Java 8 for Really Impatient ), saying , "It is illegal for a lambda expression to return a value in some branches but not in others. For example, (int x) -> { if (x >= 0) return 1; } is invalid."

Can anyone explain this ? Please provide some examples.

Thanks in advance.

I don't understand your confusion. You already have an example with an explanation. It's invalid because only one of two branches returns a value. — Sotirios Delimanolis
– Sotirios Delimanolis, Commented Mar 22, 2017 at 21:10
No matter if you write a standard method or something like the lambda expression above, the code needs to have some defined outcome. In your example, for a negative input (x) the expression is not returning anything - which is not allowed. — C-Otto
– C-Otto, Commented Mar 22, 2017 at 21:12
This book should be retitled Java 8 for Really patient. Java 8 is out for 3 years now ;-) — JB Nizet
– JB Nizet, Commented Mar 22, 2017 at 21:13
@C-Otto , Thanks for ur reply . Got it !! . Somehow missed the context — amu61
– amu61, Commented Mar 22, 2017 at 21:28

Eugene · Accepted Answer · 2017-03-22 21:12:54Z

4

I don't get it where you don't get it. Will this compile for example?

 static int test(int x) {
    if(x >= 0) {
        return 1;
    }
 }

Same goes for the lambda expression.

answered Mar 22, 2017 at 21:12

Eugene

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Comments

enders_uu · Accepted Answer · 2020-08-17 20:07:24Z

0

you have to ensure no matter "if" statement is true or false, there is always a return value or there is always not.

In your case:

illegal: (int x) -> { if (x >= 0) return 1; }
legal: (int x) -> { if (x >= 0) return 1; else return 0;}

This is because this method below is illegal

int lambda (int x){
    if (x >= 0)
        return 1;
}

edited Aug 17, 2020 at 20:07

answered Aug 17, 2020 at 19:58

enders_uu

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