Java返回语句混乱

Question

I just want to ask, what is the meaning to (--a,b)? Can somebody explain to me. Currently i just want to trace the calculation manually, but i was stuck.

This part of the code:

else if (a%2 == 0) return (-a) * b + print_it(--a, b);

Answer 1

The expression --a is the pre-decrement operator, meaning: decrement the value of a before using it in the expression. Compare it with the expression a-- , which uses the current value of a in the expression and at the end of the evaluation, decrements it.

Answer 2

The -- and ++ pre and post operators are an area where Java looks just like C or C++, but has significantly different rules.

Evaluation can never appear to be delayed, and the results are fully defined. The key concept is to separate the side effects of an operator from its value.

The general rules for expression evaluation are in Chapter 15. Expressions in the Java Language Specification. The specifics for --a are in 15.15.2. Prefix Decrement Operator -- As a side-effect, it reduces the value of a by 1. The value is the value of a after the new value is stored.

The postfix decrement has the same side-effect, performed at the same point in expression evaluation, but the value of the postfix decrement expression is the value of the variable before the new value is stored.