You may omit the braces when the lambda body is a single expression or a void method invocation. Every expression evaluates to a value, and thus cannot be void.
If the body of the lambda is a block of statements (e.g. a series of calculations followed by a return
statement), or the lambda has no value (i.e. has a void
return type) and is not a single void method invocation, you must use the block form, which requires brackets.
In a block-style lambda, if a value is return
ed, then all possible code paths must either return
a value or throw
a Throwable
.