Java Working with bits

bit, bitmask, java

Solution

If size and speed is important, use bits in a byte. (Read the links posted in the other answer as there are non-obvious complications when using and casting signed datatypes.)

This encodes for the speeds: stand, left, left_forward, forward, right_forward, and right.

public class Moo {

final static byte FORWARD = 0x1; // 00000001
final static byte LEFT     =0x2; // 00000010
final static byte RIGHT    =0x4; // 00000100

/**
 * @param args
 */
public static void main(String[] args) {

    byte direction1 = FORWARD|LEFT;  // 00000011
    byte direction2 = FORWARD|RIGHT; // 00000101
    byte direction3 = FORWARD|RIGHT|LEFT; // 00000111

    byte direction4 = 0;

    // someting happens:
    direction4 |= FORWARD;
    // someting happens again.
    direction4 |= LEFT;

    System.out.printf("%x: %s\n", direction1, dirString(direction1));
    System.out.printf("%x: %s\n", direction2, dirString(direction2));
    System.out.printf("%x: %s\n", direction3, dirString(direction3));
    System.out.printf("%x: %s\n", direction4, dirString(direction4));


}

public static String dirString( byte direction) {
    StringBuilder b = new StringBuilder("Going ");

    if( (direction & FORWARD) > 0){
        b.append("forward ");
    }

    if( (direction & RIGHT) > 0){
        b.append("turning right ");
    }
    if( (direction & LEFT) > 0){
        b.append("turning left ");
    }
    if( (direction &( LEFT|RIGHT)) == (LEFT|RIGHT)){
        b.append(" (conflicting)");
    }

    return b.toString();
}

}

Output:

3: Going forward turning left 
5: Going forward turning right 
7: Going forward turning right turning left  (conflicting)
3: Going forward turning left

Note also that Left and Right is mutually exclusive, so its possible to create an illegal combination. (7 = 111 )

If you actually meant that a thing can only move LEFT, FORWARD or RIGHT, then you don't need flags, just enums.

This enum is possible to transport in only two bits.

    enum Direction{
    NONE, FORWARD, RIGHT, LEFT;

}


Direction dir = Direction.FORWARD;
byte enc = (byte) dir.ordinal();

The final two bits in `enc` will become:

00 : none  
01 : forward;
10 : right
11 : left

Problem

Let me start by saying I have never really worked with bits before in programming. I have an object that can be in 3 states and I want to represent those states using a 3 bit array. For example: I have a race car and it can go forward,left, and right at a stand still the bits would be 000 If the car was moving forward the bits would be 010 if forward and left it would be 110 etc... How would I set the bits and how could I read them back to get the values?

Original source