I'm playing around with Java Syntax, so this is question arises purely from curiosity. This piece of code:
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Object val = 5 <- 4;
does not compile, because a label (http) "must be followed by a statement". The following two variants do compile:
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{ Object val = 5 <- 4; }
and
Object val;
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val = 5 <- 4;
In both cases, I switched from a declaration to an expression. This makes me wonder what exactly is a "statement" in Java, but the doc states:
In addition to expression statements, there are two other kinds of statements: declaration statements and control flow statements. A declaration statement declares a variable.
The JLS just says (on labels) that
The Identifier is declared to be the label of the immediately contained Statement.
It does not say anything about "expression statements".
Did I miss something, or is this just an unclear/incorrect specification?
If you read chapter 14 of the JLS a bit more carefully, you'll find that a LocalVariableDeclarationStatement is not a Statement. Not very intuitive of them, is it?
Specifically, in JLS 14.2, we see that:
So a LocalVariableDeclarationStatement is not a descendant of Statement in the hierarchy, but rather a sibling. They are both types of BlockStatements.
A label must be followed by a true Statement — that is, the specific subtype of BlockStatement that is neither a LocalVariableDeclarationStatement nor a ClassDeclaration. The various subtypes of Statement are listed in 14.5. You will not find LocalVariableDeclarationStatement among them, though you will find ExpressionStatement as a subtype of StatementWithoutTrailingSubstatement.