简单的java程序返回不正确的值

Question

Hello I am brushing up on Java practice. I have this very simple program: There are two int values, along with a boolean variable.

i) The program will return true if one of these values is negative and one is positive.

ii) However, if the boolean variable is true, the program can only return true if both int values are negative.

I have tested this out with a bunch of int values but the program seems to break once I give the method the values of (1, -1), along with the boolean value set to true. Any help or explanation would be much appreciated.

   public static void main(String[] args) {
        System.out.println(posNeg(1,-1,true));
    }
    
    public static String posNeg(int a, int b, boolean negative){
        if(negative && (a<0 && b<0)){
            return "true";
        }else if(!negative && (a<0 && b>0) || (a>0 && b<0)){
            return "true";
        }
        return "false";
    }

Answer 1

Your code breaks because of && priority .

Wrap || condition in brackets:

public static void main(String[] args) {
    System.out.println(posNeg(1,-1,true));
}

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

Answer 2

&& has higher precedence than || , so in else if condition ie !negative && (a<0 && b>0) || (a>0 && b<0) first this condition is evaluated !negative && (a<0 && b>0) then the result of this is evaluated with res || (a>0 && b<0).

In your case I guess you want to first evaluate || then && , so just put a bracket like this in !negative && ( (a<0 && b>0) || (a>0 && b<0)) , so that first the condition inside bracket is evaluated , then that result is evaluated with &&

public class Main
{
     public static void main(String[] args) {
        System.out.println(posNeg(1,-1,true));
    }
    
    public static String posNeg(int a, int b, boolean negative){
        if(negative && (a<0 && b<0)){
            return "true";
        }else if(!negative && ((a<0 && b>0) || (a>0 && b<0))){
            return "true";
        }
        return "false";
    }
}

Answer 3

public static void main(String[] args) {
    System.out.println(posNeg(1,-1,false));
}

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