Boolean method doesn't work like it should

Question

So I really don't get what I did wrong here. The method should take a boolean array and check if all elements are true, if one is false it should return false.

public static boolean nvm(boolean[] con) {
    boolean c = true;

    for(int i = 0; i < con.length ; i++) {
        if (and(con[i], con[i++]) == false) {
            c = false;
        }
    }
    return c;
}

The and check two booleans, if they're both true it returns true, otherwhise false. I have already tested and, but its working fine.

Wrote the post on my mobile, so I hope it doesn't looks weird. Thankful for any help.

I wonder how much time you've spent by thinking about the usage of `i++`. Does this code really makes sense to you? — Tom, Jul 02 '17 at 09:58
Doesn't work with `break;` either. I take [true,true,false,true] as testarray and it returns true, while it should return false. — IPiiro, Jul 02 '17 at 10:03
i++ <=> i = i + 1. Still doesn't get what's the problem with that — IPiiro, Jul 02 '17 at 10:05
Very surprised you get any result at all; I'd have expected an `IndexOutOfBoundsException` — Kevin Anderson, Jul 02 '17 at 10:06
`i++ <=> I=I+1`:. not so much a problem in your `for` statement; becomes a problem when you do it _again_ inside the loop — Kevin Anderson, Jul 02 '17 at 10:09
Ye I got it, didn't realize that the `i++` would affect the `i` because I just use it as an index — IPiiro, Jul 02 '17 at 10:13
Not only that, `con[i],con[i++]` makes also no sense. And no, `i++` is not the same as `i = i + 1`. — Tom, Jul 02 '17 at 10:13
Didn't use java for a long time and was just refreshing my knowledge. — IPiiro, Jul 02 '17 at 10:34
@Tom so where is exactly the difference between i++ and i = i + 1 ? — IPiiro, Jul 02 '17 at 10:36

PeterMmm · Answer 1 · 2017-07-02T10:03:04.640

2

The method should take a boolean array and check if all elements are true

for(int i = 0; i<con.length ; i++){
     if(!con[i]) return false;
}

edited Jul 02 '17 at 10:03

answered Jul 02 '17 at 09:58

PeterMmm

24,152
13
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Wow.. that is so damn obvious... I guess I'm still asleep :D – IPiiro Jul 02 '17 at 10:04
@BackSlash No, it most certainly is not. – user207421 Jul 02 '17 at 10:10

score 1 · Accepted Answer · answered Jul 02 '17 at 10:03

1

Problem is in this line:

if(and(con[i],con[i++]) == false){

Particularly with i++ part. i++ actually increases i, so you may skip some array elements and get a wrong result. Use i+1 instead, which would leave i unchanged.

Also, you can simplify your code like this:

public static boolean nvm(boolean[] con) {
    for(int i = 0; i < con.length ; i++) {
        if (!con[i]) return false;
    }

    return true;
}

answered Jul 02 '17 at 10:03

Max

915
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Oh but I didn't realize this `i++` "really" affects the i as the counter – IPiiro Jul 02 '17 at 10:08

Thomas Jungblut · Answer 3 · 2017-07-02T10:11:08.060

1

Maybe I'm missing something but

'The method should take a boolean array and check if all elements are true, if one is false it should return false'

can be written as:

boolean[] array;
for(boolean a : array) {
  if(!a) { return false; }
}
return true;

edited Jul 02 '17 at 10:11

answered Jul 02 '17 at 10:04

Thomas Jungblut

20,854
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score 1 · Answer 4 · answered Jul 02 '17 at 10:07

If you you want to check that all elements are true you can easily simplify your code.

public static boolean nvm(boolean[] con) {
    for(int i = 0; i<con.length ; i++) {
        If(!con[i]) {
            return false;
        }
    }
    return true;
}

I do not see any reason for the "and". I can only see that it may cause you to have an idexoutofboundsexception.

Boolean method doesn't work like it should

4 Answers4