Java编译器错误没有任何意义（ <identifier> 预期）

Question

I have done a lot of searching for what this compiler error <identifier> expected means, and none of them seem to apply to my situation. Really sorry if this is a duplicate or basic info, but I can't find anything anywhere.

The following code works fine. Note that I am positive myObject1 is indeed a HashSet<String> so the cast is ok.

@SuppressWarnings("unchecked")
HashSet<String> s1 = (HashSet<String>) myObject1;

The following code does NOT work fine. It will compile, but with warnings.

@SuppressWarnings("unchecked")
HashSet<String> s1;
s1 = (HashSet<String>) myObject1;

So then I try the code below.

@SuppressWarnings("unchecked")
HashSet<String> s1;
@SuppressWarnings("unchecked")
s1 = (HashSet<String>) myObject1;

Now it refuses to even compile, giving me the <identifier> expected error that is puzzling me so much. The ^ symbol in my command line is pointing right before the = in the last line. I'm not sure what on earth I could be expected to put BETWEEN the s1 and the = .

Any ideas? Thanks!

Answer 1

You can't apply an annotation to a simple assignment statement. From section 9.7 of the JLS :

Annotations may be used as modifiers in any declaration, whether package (§7.4.1), class (§8.1.1) (including enums (§8.9)), interface (§9.1.1) (including annotation types (§9.6)), field (§8.3.1, §9.3), method (§8.4.3, §9.4), formal parameter (§8.4.1), constructor (§8.8.3), or local variable (§14.4.1).

I agree that the compiler error message could be rather clearer, admittedly...

Answer 2

You could look at the Java Api for Annotations.

http://docs.oracle.com/javase/6/docs/api/java/lang/SuppressWarnings.html

http://docs.oracle.com/javase/6/docs/api/java/lang/annotation/ElementType.html#LOCAL_VARIABLE

There you can see, that SupressWarnings has the target LOCAL_VARIABLE.

And LOCAL_VARIABLE stands for the declaration not the assignment.