How to check if an integer can be divided by 3

Question

How to check if my integer can be divided by 3 as below:

for(int i=0; i<24;  i++){
   //here, how to check if \"i\" can be divided by 3 completely(e.g. 3,         


        

Answer 1

If you are using a loop, you can use the fact that every third number can be divided by 3.

for(int i = 0; i < 24;  i += 3) {
   System.out.println(i + " can be divided by 3");
   System.out.println((i+1) + " cannot be divided by 3");
   System.out.println((i+2) + " cannnot be divided by 3");
}

This avoids the need for a modulo and cuts the number of loops by a factor of 3.

Answer 2

Use the modulo operator.

if(i % 3 == 0)

Also see Modulo operation at Wikipedia

Answer 3

Check the remainder of i devided by 3

if (i % 3 == 0) {}

Answer 4

Use the MOD operator

for(int i=0; i<24;  i++){
   if( i%3 == 0 )
       // It is divisible by 3

}

Answer 5

if( i % 3 == 0 )

The % operator delivers you the rest of the division i / 3

Answer 6

Well, what you could do (it might be a bit faster; it is faster on my machine) is:

boolean canBeDevidedBy3 = ((int) (i * 0x55555556L >> 30) & 3) == 0;

instead of

boolean canBeDevidedBy3 = (i % 3) == 0;

However, the multiplication trick only works for -2 <= i <= 1610612735. This answer was inspired by this optimization question. But if I can give you a tip: use (i % 3) == 0. It's so much simpler, and will always work.