how does Operators such as NOT(!), AND(&&) etc work in java?

Question

please help me i cant figure out how does the operators(AND, NOT, XOR ,,..ETC) work in java. I know the output of AND and OR but i am clueless at NOT. For example i don't completely understand statement such as a variable != integer(i!= 3). i mean how does the NOT operator work.for example how does NOT work here.

class Demo {

    public static void main(String args[]) throws java.io.IOException {
        char ch;

        do {

            System.out.print("Press a key followed by ENTER: ");

            ch = (char) System.in.read(); // get a char

        } while (ch != 'q');

    }

}

In your case you loop until ch input is not equal to `q` this is what mean `!=` — Youcef LAIDANI, Jun 17 '17 at 17:52
That's the "not equal to" operator. The "not" operator is '!' Do you know what it means for a number to be different from 3? — molbdnilo, Jun 17 '17 at 17:57
Oh okay. does that mean if (i != 3) means 3 not equal to i. i don't get this concept when it comes to integer. — Chris John, Jun 17 '17 at 17:58
sorry guys i'm new to programming and some things i don't get it — Chris John, Jun 17 '17 at 17:59
@ChrisJohn don't worry about it, everybody at first was, well, a beginner, so don't worry — developer_hatch, Jun 17 '17 at 18:02
http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op2.html — Lew Bloch, Jun 17 '17 at 18:17

developer_hatch · Accepted Answer · 2017-06-17T18:05:34.970

0

if you make some System outs you will figure out:

char ch = 'l';
System.out.print(2 != 3);
--true, they are not equal
System.out.print('q' != 'q');
-- false, they are equals
System.out.print(ch != 'q');
-- true, they are not equals

it means, they != checks if they are exactly the same (be careful in this case is used for primitive types, such as int, char, bool, etc. this operator work differently in objects, such as String)

edited Jun 17 '17 at 18:05

answered Jun 17 '17 at 17:56

developer_hatch

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`'q'` is a `char`, not a `String`. – molbdnilo Jun 17 '17 at 17:58
@molbdnilo you are totally right, i was editing just right now – developer_hatch Jun 17 '17 at 18:00
1

@Aominè also right, I read fast and didn't notice the simple quote 'q', I thought it was "q", thanks a lot – developer_hatch Jun 17 '17 at 18:01
System.out.print(ch != 'q'); -- true, they are equals .... how does this becomes true ch is 1 right..so.. – Chris John Jun 17 '17 at 18:03
@ChrisJohn aaah ! you find my error, see, it 'was at purpose so I was testing you (no that's a joke! haha it was my mistake) they are not equals – developer_hatch Jun 17 '17 at 18:04
@ChrisJohn I updated, ch = 'l', so ch != 'q' is true :), I hope that was helpul – developer_hatch Jun 17 '17 at 18:06
@DamianLattenero thanks you sir and also thanks for the support. and now i get it kind off but not totally. .so the last part of the program doesnt sysout right! – Chris John Jun 17 '17 at 18:08

notphilphil · Answer 2 · 2017-06-17T21:06:12.250

0

The ! operator is unary. When applied to Boolean values it switches, for example

bool on = true;
System.out.print(!on); //false
System.out.print(on); //true

When used next to an equal sign, it checks if the values are not equal. If they are not equal, it returns true. Otherwise, it returns false. For example,

int two = 2;
int three = 3;
System.out.print(two != three); 
//returns true, since they are not equal
System.out.print(two == three);
//returns false, since they are not equal

edited Jun 17 '17 at 21:06

answered Jun 17 '17 at 18:08

notphilphil

385
5
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"the `!` operator is binary." Actually, it's a unary operator http://docs.oracle.com/javase/tutorial/java/nutsandbolts/op1.html http://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.15.6 – Lew Bloch Jun 17 '17 at 18:20
"When [`!` is] used next to an equal sign" Some might misconstrue this to mean that `!=` comprises two tokens, or two operators concatenated, which it does not. `!=` is a single operator and parsed as a single Java token. – Lew Bloch Jun 17 '17 at 18:25
"Just like `&&` and `||`, the `!` operator is unary." The `&&` and `||` operators are not unary. Neither is `!=`. Nor `==`. – Lew Bloch Jun 17 '17 at 21:00

score 0 · Answer 3 · answered Jun 17 '17 at 18:16

int x = 4;
int y = 5;

!case a means not case a

x == y means x and y are referencing the same place in memory (to understand what that means, see this question).

x != y is the opposite of the above, and is the same as writing !(x == y) (not x equals y)

case a && case b And operator - Both case a and case b are true.

case a || case b Or operator - Either case a or case b are true.

Here are same examples so everything is clearer:

1==1 // true, as 1 is equal to 1
2==1 // false, as 1 is not equal to 2.
!true // false, as not true is false.
1!=1 // false, as 1 is equal to one.
!(1==1) // The same as above - exact same output.
// You need the brackets, because otherwise it will throw an error:
!1==1 // Error - what's '!1'? Java is parsed left-to-right.
true && false // false - as not all cases are true (the second one is false)
true || false // rue - as at least one of the cases are true (the first one)

how does Operators such as NOT(!), AND(&&) etc work in java?

3 Answers3