bitmask question?

Question

I have the follow:

public static final int LIMIT_ONE = 1;
public static final int TRADEABLE = (1 << 1);
public static final int SELLABLE = (1 << 2);
         


        

Answer 1

12414 in binary is:

Binary number: 1  1  0  0  0  0  0  1  1  1  1  1  1  0
-------------------------------------------------------
Bit positions: 13 12 11 10 9  8  7  6  5  4  3  2  1  0

Look at which bits are 1. Those are the flags that are set in the bitmask, which is created by using the bitwise OR operator to combine the flags:

bitmask = TRADEABLE | SELLABLE | STORABLE | STORABLE_IN_WH | STORABLE_IN_LEGION_WH | BREAKABLE | BLACK_CLOUD_TRADERS | CAN_SPLIT;

To further explain this, STORABLE = (1 << 3); means that STORABLE is equal to the number one (binary 1, falling only in bit position 0) shifted to the left by 3 places. Note that STORABLE = Math.pow(2, 3); would be equivalent. Because none of the bits overlap among the flags, we can combine all of them into a single int and then split them apart later.

We can check for the existence of flags using the bitwise AND operator, which will return a non-zero value if the flag is set and a zero value if the flag is not set:

if(bitmask & TRADEABLE != 0) {
    // This item can be traded
} else {
    // This item cannot be traded
}

We can set, clear, or toggle flags like this:

bitmask |= TRADEABLE; // Sets the flag using bitwise OR
bitmask &= ~TRADEABLE; // Clears the flag using bitwise AND and NOT
bitmask ^= TRADEABLE; // Toggles the flag using bitwise XOR