java - Why won't javac accept `x = x+++++y`? -


from perspective of compiler theory, why javac compiler not accept statement of form x = x+++++y accept x = x+++ ++y ?

because ++ valid token java lexer, statement x+++ ++y parsed tokens :

(x)(++)(+)( )(++)(y)

whereas x+++++y tokenized invalid:

(x)(++)(++)(+)(y)

the above invalid java because ++ operator can applied things numeric variables, result of (x++) not. type of tokenizing great example of concept known maximal munch.

from jls section 3.2

the longest possible translation used @ each step, if result not make correct program while lexical translation would.

thus, input characters a--b tokenized (§3.5) a, --, b, not part of grammatically correct program, though tokenization a, -, -, b part of grammatically correct program.


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