About Question enthuware.ocpjp.v17.2.1208 :

[likejudo]

I am trying to understand why this fails to compile

Code: Select all

       final Device d;
[i]        try(d = new Device()){
[/i]            d.open();
            d.read();
            d.writeHeader("TEST");
            d.close();
        }catch(IOException e){
            System.out.println("Got Exception");
        }

java: the try-with-resources resource must either be a variable declaration or an expression denoting a reference to a final or effectively final variable

[admin]

Is it a variable declaration? Obviously, no.
Is it an expression denoting a reference to a final or effectively final variable? No, it is an expression denoting a reference to a Device object.

[likejudo]

Is it an expression denoting a reference to a final or effectively final variable? No, it is an expression denoting a reference to a Device object.

But even when I made it final (please see snippet above) it would not compile.

[admin]

Yes, I saw that and that is what I addressed. You made d final. But the expression that you have inside try is not d. It is d = new Device(). The value of this expression is a reference to a Device object. The value of this reference is not d although d does point to the same Device object.

[admin]

If you are not sure what these statements mean, "But the expression that you have inside try is not d. It is d = new Device().", please go through section 6.1.2 Expressions and Statements of this book. I have attached the relevant pages here.

section_6_1_2_hanumant_deshmukh_1z0-815_fundamentals_1.png (183.77 KiB) Viewed 2066 times

[likejudo]

thank you

[lowlysute]

I am trying to understand why this fails to compile drift hunters

Code: Select all

       final Device d;
[i]        try(d = new Device()){
[/i]            d.open();
            d.read();
            d.writeHeader("TEST");
            d.close();
        }catch(IOException e){
            System.out.println("Got Exception");
        }

java: the try-with-resources resource must either be a variable declaration or an expression denoting a reference to a final or effectively final variable

The issue with the provided code is related to the usage of the try-with-resources statement in Java. The try-with-resources statement is used to automatically manage the closing of resources, such as files, sockets, or other objects that implement the AutoCloseable interface.