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Programmer Certification (OCPJP)

Simon Roberts class. Bewildered why no compiler error storing a double in a long nor a long in int?

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from a Simon Roberts class one year ago, I made this note but could not understand, why no compiler error storing a double in a long nor a long in int?

output:

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-1

Campbell Ritchie

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Have you read the Java® language Specification about compound assignment operators?

Anil Philip

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Campbell Ritchie wrote:Have you read the Java® language Specification about compound assignment operators?

I have never read the JLS because I am preparing for the Java Certification exam and one of the recommended resources is the Boyarsky-Selikoff Complete Study Guide for the Java Certification exam.
To learn Java before, I used to read the Sun Java online tutorial and Cay Horstman's Java 11 book. The Java online tutorial stopped being updated after Java 8.

Paul Clapham

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The JLS wrote:A compound assignment expression of the form E1 op= E2 is equivalent to E1 = (T) ((E1) op (E2)), where T is the type of E1, except that E1 is evaluated only once.

I believe that explains the question you asked?

Campbell Ritchie

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Anil Philip wrote:. . . I have never read the JLS . . . .

You ought to. As Paul shows, you would have known the answer. The JLS is the definitve source of information; it is an instruction manual for what a Java® implementation must do and not do.

Paul Clapham

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It's far from the ideal teaching tool, though, in its mind-numbing level of detail.

On the other hand I searched the web for explanations of how the += operator works. I found several quickly, but none of them mentioned the implicit cast which was the key feature in the question in the OP. Even Oracle's tutorial doesn't mention it. Whether Anil's recommended resources mentioned the cast, I don't know.

Campbell Ritchie

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Anil Philip wrote:from a Simon Roberts class one year ago . . .

Please post a link so we can check the original to see whether there was any explanation about the casts in the original.

Mike Simmons

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Of course, if Simon's course is paid content, it's unlikely we can get a shareable link.

I wonder, does Boyarsky & Selikoff explain that compound assignment operators have an implicit cast? Of course, that's another paid resource, and I don't have a copy. But I think Anil does...

Anil, I know the JLS can be a pain to read. But it is often the best resource to explain some of the subtle points that slip through the cracks of other resources.

Campbell Ritchie

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Mike Simmons wrote:. . . the JLS can be a pain to read. . . .

But not the part relevant to this question.

Mike Simmons

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True. Often the hardest part is simply figuring out where in the JLS the rule you need is located. But again, in this case that's pretty straightforward. So I would say, it's worthwhile for programmers to get in the habit of at least trying the JLS as a source of answers... but it's also understandable if they don't always find it terribly helpful.

Anil Philip

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Campbell Ritchie wrote:

Anil Philip wrote:from a Simon Roberts class one year ago . . .

Please post a link so we can check the original to see whether there was any explanation about the casts in the original.

No, but I can post a screenshot. 😒

Campbell Ritchie

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If you can post a screenshot, surely you can copy'n'paste the code instead.

Anil Philip

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Campbell Ritchie wrote:If you can post a screenshot, surely you can copy'n'paste the code instead.

No, it's not code.

Consider Paul's rocket mass heater.