Why does this return true?

Question

I recently started to teach myself Java, after playing around with CodingBat I am left with an extremely basic question. Why is this returning "true"?

a = 1, b= -1, negative = true

public boolean posNeg(int a, int b, boolean negative) {
  if(!negative && a <= 0 && b >= 0 || a >= 0 && b <= 0){
    return true;
  }else if(negative && a <= 0 && b <= 0){
    return true;
  }
  return false;
}

Answer 1

In:

!negative && a <= 0 && b >= 0 || a >= 0 && b <= 0

the higher precedence of && than || means it is the same as:

(!negative && a <= 0 && b >= 0) || (a >= 0 && b <= 0)

The conditional-or operator ( || ) will return true if either of its operands are true:

• !negative && a <= 0 && b >= 0 is false, because negative is false (as is b >= 0 , but that's not evaluated);
• a >= 0 && b <= 0 is true

Hence the expression is true , and so the if statement is executed, meaning that true is returned.

Answer 2

because :

if (!negative && a <= 0 && b >= 0 || a >= 0 && b <= 0) {
//---(false)------(true)----(false)-----(true)----(true)

The trick is with || :

false && true && false -> false
true && true -> true

---

(false && true && false) || (true && true) ----> true
     false               ||     true       ----> true

Answer 3

在您的第一个if if(!negative && a <= 0 && b >= 0 || a >= 0 && b <= 0){ A大于0，b小于0的情况下，返回true。