| operator in Java

Question

I've got this statement in Java:

System.out.println(3|4); 

Why is the output 7? I can't understand, can someone help me?

Answer 1

It's doing a bitwise OR operation, and 3 OR 4 is 7.

See here: http://en.wikipedia.org/wiki/Bitwise_OR#OR

Answer 2

It's a bitwise OR operation. It's modifying things at a binary level.

             011                     3
in binary: | 100     in decimal:  |  4
             ___                   ___
             111                     7

Open Windows calc using scientific mode. You can flip between decimal and binary (and hex) and perform bitwise operations including or, and, xor, etc.

To do a bitwise or in your head or on paper, compare each digit of the same ordinal. If either number is a 1, the result at that ordinal will be 1.

Answer 3

The operator | does a "bitwise OR". The output of bitwise OR on two bits is 1 if either bit is 1 or 0 if both bits are 0. Bitwise OR on two numbers just does a bitwise OR on each bit individually.

Heres how 3|4 works:

  3:  00000011
  4:  00000100
--------------
3|4:  00000111 = 7

Answer 4

| is the "bitwise or" operator. in a|b, if nth bit of a and/or b is 1, the nth bit of the result will be 1. 3 is 11 in binary. 4 is 100 in binary.

0  1  1
or or or
1  0  0
=  =  =
1  1  1

And 111 happens to be the binary representation of 7.

Answer 5

Binary representation:

 3 = 00000011
 4 = 00000100

| is bitwise OR operator

when you OR two numbers, you take the binary representation and the OR result is 1 IFF for that column at least one column is set true (1)

So

00000011
00000100
--------
00000111

then, columns tell you the value at that position:

128, 64, 32, 16, 8, 4, 2, 1

so

128, 64, 32, 16, 8, 4, 2, 1
 0 ,  0,  0,  0, 0, 1, 1, 1  

any column with a 1 means you add that column's value:

4 + 2 + 1 = 7

Answer 6

As bitwise operators can be a little confusing without something to correlate them to, the way I've explained their function to non-programmers even is that you simply subtitute 1 for true and 0 for false, and then they behave identically to the operators in the english language:

the moon is blue AND the sky is blue, is false

0 and 1 is 0

the moon is blue OR the sky is blue, is true

0 or 1 is 1

but the analogy breaks down when I get to:

the ocean is blue XOR the trees are green, is false

Answer 7

It's useful to realize there is a generalized system for counting underlying this. Binary is base-2. Familiar decimal is base-10. Linux permission octal is base 8.

A number's value is obtained by adding together the individual values of each of its digits. For any digit, the value is derived from a simple formula.

(digit) * (base) ^ (number of places to the left of the decimal point)

123 = one hundred and twenty three = (1 * 10^2) + (2 * 10^1) + (3 * 10^0) = 100 + 20 + 3

I learned that in CS211 (not bragging, just remembering)