Why must throw statements be enclosed with a full code block in a lambda body?

Question

If there is a single statement in a lambda function, we can omit defining the full code block for it:

new Thread(() -> System.out.println());

Answer 1

AFAIK The jls says that the lambda body has to be:

expression or a block. Having it like this:

new Thread(() -> throw new RuntimeException());

is neither and the compiler somehow informs you about that.

Declaring it like this:

 new Thread(() -> {
     throw new RuntimeException();
 });

makes it a block. Here is the relevant part:

A block is a sequence of statements, local class declarations, and local variable declaration statements within braces.