Java Working with bits
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... 开发者_Python百科How would I set the bits and how could I read them back to get the values?I would suggest using BitSet along with enum's
enum State { LEFT, RIGHT, FORWARD,STAND_STILL}
BitSet stat=new BitSet(4);
void setLeft() // and so on for each state
{
stat.set(State.LEFT);
}
boolean isLeft()
{
stat.get(State.LEFT);
}
void reset() //reset function to reset the state
{
stat.clear();
}
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
The least you'll need to store these three bits is one byte
.
Read this tutorial on bitwise operators to get started.
Edit: this page on bit masks may also be very helpful.
You say three states, but you've actually got six: forward, forward-left, forward-right, left, right, stand-still. Unless your race car doesn't move sideways ofcourse, then you've got four.
You should really use an enum for this:
enum State { FORWARD, FORWARD_LEFT, FORWARD_RIGHT, STAND_STILL }
Since left, right and forward are mutually exclusive, this isn't a very good fit for a bit-fiddling program. You'll get into all kinds of consistency problems.
In java.util there is a class called BitSet that makes bit manipulation very simple.
In your case you could create a BitSet of size 3 and then use the get() and set() methods to set a check the bits.
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