Need explanation of one Java If-Else logic

Question

I need explanation of the below code execution

public static void main(String[] args) {
    Long tail = 2000L;
    Long distance = 1999L;
    Long story = 1000L;
    if ((tail > distance) ^ ((story * 2) == tail))
        System.out.println("a");
    if ((distance + 1 != tail) ^ ((story * 2) == distance))
        System.out.println("2");

}

After the code execution no output is produced.

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/opsummary.html — cremersstijn, Sep 18 '13 at 13:15
Remember that the ^ operator can be thought of as __this or that, but not both__. — Øyvind Robertsen, Sep 18 '13 at 13:15

score 5 · Accepted Answer · edited May 23 '17 at 12:23

5

^ stands for XOR operation of 2 booleans, in below statement

if ((tail > distance) ^ ((story * 2) == tail))

(tail > distance) is true

((story * 2) == tail) is true

and true XOR true is false

edited May 23 '17 at 12:23

Community

1
1

answered Sep 18 '13 at 13:12

sanbhat

17,522
6
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score 3 · Answer 2 · answered Sep 18 '13 at 13:22

3

the XOR output table looks like this:
X Y Output
0 0 0
1 0 1
0 1 1
1 1 0

So based on both your booleans being true you will get a false return from the if statements.

answered Sep 18 '13 at 13:22

Rushfire

56
3

score 1 · Answer 3 · answered Sep 18 '13 at 13:22

public static void main(String[] args) {
    Long tail = 2000L;
    Long distance = 1999L;
    Long story = 1000L;
    if ((tail > distance) ^ ((story * 2) == tail))
        System.out.println("a");
    if ((distance + 1 != tail) ^ ((story * 2) == distance))
        System.out.println("2");
}

if (((tail > distance) ^ ((story * 2) == tail)) == true)
            System.out.println("a");

is equal to:

if (((2000 > 1999) ^ ((1000 * 2) == 2000)) == true)
            System.out.println("a");

is equal to:

if ((true ^ true) == true)
            System.out.println("a");

is equal to:

if (false == true)
            System.out.println("a");

and therefor it's never printed.

Similar reasoning applies to the second if-else statement.

score 0 · Answer 4 · answered Sep 18 '13 at 13:13

0

Both your conditions are false thats why you have no output

answered Sep 18 '13 at 13:13

Prasad Kharkar

13,410
5
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score 0 · Answer 5 · answered Sep 18 '13 at 13:14

You never have anything returned as there isn't anything to return - both conditions are false.

Also I'm fairly sure it should be written as

if ((tail > distance) ^ ((story * 2) == tail)) {
    System.out.println("a");
}
if ((distance + 1 != tail) ^ ((story * 2) == distance)) {
    System.out.println("2");
}

You could also test it by saying

if ((tail > distance) ^ ((story * 2) == tail)) {
    System.out.println("a");
} else {
    System.out.println("Condition 1 False");
}
if ((distance + 1 != tail) ^ ((story * 2) == distance)) {
    System.out.println("2");
} else {
    System.out.println("condition 2 False");
}

Alternatively, did you mean to write

if ((tail > distance) || ((story * 2) == tail)) {
    System.out.println("a");
}
if ((distance + 1 != tail) || ((story * 2) == distance)) {
    System.out.println("2");
}

Using the logical OR instead?

score 0 · Answer 6 · answered Sep 18 '13 at 13:17

0

You may be missing a basic understanding of the difference between 'or' and 'exclusive-or'. The exclusive-or condition a ^ b is true only if (a is true and b is false) OR (a is false and b is true).

answered Sep 18 '13 at 13:17

fred02138

3,323
1
14
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score 0 · Answer 7 · answered Sep 18 '13 at 13:20

0

^ is XOR. Which is almost the opposite of OR.

OR:

True True = True
True False = False
False True = False
False False = False

XOR:

True True = False
True False = True
False True = True 
False False = False

answered Sep 18 '13 at 13:20

Arash Saidi

2,228
20
36

I know, I know, true and false are low case in Java. – Arash Saidi Sep 18 '13 at 13:21

Need explanation of one Java If-Else logic

7 Answers7