询问try-with-resources语句

Question

Just confirming that the following does not compile and it's not a mistake of mine:

try(Files.newBufferedWriter(Paths.get("/home/user/Desktop/TryItOutMan.txt"), Charset.defaultCharset())
        {
        }
        catch(IOException io){io.printStackTrace();}

However the following compiles:

try(BufferedWriter bw =Files.newBufferedWriter(Paths.get("/home/user/Desktop/TryItOutMan.txt"), Charset.defaultCharset())
        {
        }
        catch(IOException io){io.printStackTrace();}

It seems that the compiler check whether or not the classes declared in the try-catch-with-resources statement implement AutoClosable ... however It could have worked since the method returns a BufferedWriter which implements AutoClosable .

Just asking for a confirmation that

try(Files.newBufferedWriter(Paths.get("/home/user/Desktop/TryItOutMan.txt"), Charset.defaultCharset())

does not compile.

Thanks in advance.

Answer 1

If you look at the syntax definition of the try-with-resources in the JLS , you will see that it expects a variable name. So it must look like:

try (SomeType variable = xxx;)

Answer 2

The Java tutorial states:

The try -with-resources statement is a try statement that declares one or more resources.

In your first snippet, you don't declare a resource:

Files.newBufferedWriter(Paths.get("/home/user/Desktop/TryItOutMan.txt")

Whilst in your second snippet, you do:

BufferedWriter bw = ....