Java coding: How to use "&" and "|" ?

Those operate on the individual bits.

&& and || are used to combine boolean values, as in, "true" and "false".

& and | are used to combine the bits of integers.

As an example, 7 is 111, and 3 is 11 or 011.

So 7 & 3 is 3, since the leftmost bit is zero for 3.

But 7 | 3 is 7, since all bits are one for 7.

It's not always one number or the other though.

12 is 1100.

3 is 0011.

Thus 12 & 3 is 0, since none of the four bits is 1 for both numbers.

12 | 3 however is 15, since every bit is 1 in at least one number.

The next question is: when do we actually USE them?

One example is a situation where we only care about certain bits. For instance each odd number has its rightmost bit set to 1. Which means the expression x & 1 is 1 if x is odd, 0 if x is even.

Another use case is flags; each bit can be considered a variable, so we can introduce constants like Player.IS_MALE or Player.IS_NPC and set them to numbers like 1, 2, 4, 8, 16, etc.

That way we can combine the bits using |:

Player player = new Player("Guy", Player.IS_MALE | Player.IS_NPC);

Assuming that Player.IS_MALE is 4, or 100, and assuming that Player.IS_NPC is 16, or 10000, we are passing 20 to the constructor, or 10100.

So a single parameter is used to convey multiple true/false choices.

Inside the constructor, we can read the individual bits using

if (x & Player.IS_MALE > 0) ...

& and | can be used in logical statements as well, HOWEVER it does not short circuit. Unlike the && and || operators. For example given:

false && BOOLEAN, we know the result is false, we don't need to know what the other boolean value is.

Given:

true || BOOLEAN, the same is true, any value OR'd with true is true.

The & and | are bitwise operators, they perform their respective operations on a bit by bit basis. When used for logical operations they DO NOT use short circuit evaluation, meaning they evaluate all expression, performing correct precedence (I believe & is higher up than | ), and evaluating like so.

Pretty sure this is how the bitwise ones work on booleans as well..