Tim Bant

Hi all and Happy New Year!

I wanted to ask a quick q regarding string pools. I understand the concept of it however when testing my knowledge on the SE17, I came across the following snippet:

String s1 = """    purr"""; String s2 = ""; s1.toUpperCase(); s1.trim(); s1.substring(1, 3); s1 += "two"; s2 += 2; s2 += 'c'; s2 += false; if ( s2 == "2cfalse") System.out.println("=="); if ( s2.equals("2cfalse")) System.out.println("equals"); System.out.println(s1.length());

My question is, since String pools are related to compile time values, is += operation considered a runtime operation, whereas a simple concatenation of say:

String s2 = "2"+'c'+false;

is considered compile time (and would ultimately return == on line 14 if applied correctly)?

Just trying to clarify for myself why 14 is considering it as false.

Thanks

Understood, will bear that in mind for my re-take. Thanks!

What's the "answer" / recommendation in that scenario then if undefined isn't an answer? Thanks

Makes sense, thanks for clarifying for me!

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 {}

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

Thanks Carey, trying to study for the exam so saw this example and couldn't quite work it out

If a line of code has an explicit cast, then does the cast happen before or after the arithmetic?

For example (I know this doesn't compile, but trying to understand why...)


long addCandy(double fruit, float veg) { return (int) fruit + veg; }


I believe the cast happens first? Using the example above, fruit is casted to an int, however, we are then trying to add a float to an int, which the compiler doesn't like...? Or is it that float is bigger than a long when dealing with promotion?

Morning,

why doesn't the add line here work?

public static void add (List <? extends Number> list) { list.add(1234); }

I would have thought since Integer extends Number it should allow it?

Thanks as always

ah, got you - so that explains now why, if I add a return to the new Exception, it compiles

Callable c3 = () -> {return new Exception();};

so my understanding is that the "throw" in the below is an equivalent to a return in this scenario, would that be fair?

Callable c = () -> {throw new Exception();};

Hi all,
Why is the code below an acceptable Callable command?

Callable c = () -> {throw new Exception();};

I get why this is one here is, because its returning an Exception object:
Callable c2 = () -> new Exception();


Interestingly, the first example won't work without brackets, so it makes me a little more confused...any ideas?

Thanks

Thanks Mike

ah, that makes total sense, thanks Mike

Hi all,

I've been doing some practice tests on streams. One of the questions had the following:

List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17); //1 Stream<Integer> primeStream = primes.stream(); //2 Predicate<Integer> test1 = k->k<10; //3 primeStream.collect(Collectors.partitioningBy(test1, Collectors.counting()))      .values().forEach(System.out::print);

And its explanation was that the output is not 100% guaranteed to be 3 4 or 4 3. Why is that? I thought when it came to parallel streams the output can vary.

Thanks

Hi (Oi) Joao,

I had this thought before I started studying - however, I went down the book route OCP Oracle Certified Professional Java SE 17 Developer Study Guide by Scott Selikoff, Jeanne Boyarsky and use the internet for further /deeper queries. I have my exam in a few weeks time - it certainly feels like I have been studying for way more than 35 hours that is for sure...