[Solved] =- operator in java

Question

-- is a “decrement” operator in Java and many other languages. The reason the compiler doesn’t treat it as two - operators is that there’s a basic rule that the compiler will look for the longest sequence of consecutive characters that forms one of its “separators” or “operators”, as defined here. (> characters are handled a bit differently because of generics.)

This is explicitly stated in JLS 3.2:

The longest possible translation is used at each step, even if the
result does not ultimately make a correct program while another
lexical translation would. There is one exception [for > characters]…

Thus, when the compiler sees --4, it treats it as a -- operator applied to 4, which is illegal. It doesn’t backtrack and try to find other ways to interpret the --.

But if it sees - -4, with a space between the hyphens, it can’t interpret the - as anything else except individual minus signs. This is legal and has the same meaning as -(-4).

Accepted Answer

-- is a “decrement” operator in Java and many other languages. The reason the compiler doesn’t treat it as two - operators is that there’s a basic rule that the compiler will look for the longest sequence of consecutive characters that forms one of its “separators” or “operators”, as defined here. (> characters are handled a bit differently because of generics.)

This is explicitly stated in JLS 3.2:

The longest possible translation is used at each step, even if the
result does not ultimately make a correct program while another
lexical translation would. There is one exception [for > characters]…

Thus, when the compiler sees --4, it treats it as a -- operator applied to 4, which is illegal. It doesn’t backtrack and try to find other ways to interpret the --.

But if it sees - -4, with a space between the hyphens, it can’t interpret the - as anything else except individual minus signs. This is legal and has the same meaning as -(-4).