位图数据结构及其在 Java和 Redis中的应用

原来值 :     000000000000000000000000001000
1右移10位:   000000000000000000010000000000

或操作的结果: 000000000000000000010000001000   ----> 可以直接表示 3 和 10 两个位上都为1了.

原来值 :              000000000000000000010000001000    ----> 10和3上为1,
1右移3位:             000000000000000000000000001000
1右移3位取非后:        111111111111111111111111110111

原来的值与取非后取与:   000000000000000000010000000000   ----> 只有10上为1了.

当前值:        000000000000000000010000001000
1右移10位:     000000000000000000010000000000

与操作的结果:   000000000000000000010000000000    ---> 只要这个数字不等于0,即说明10上为1,等于0则为0.

/**
 * Created by pfliu on 2019/07/02.
 */
public class BitMapTest {
    // 实际使用int数组存储
    private int[] data;

    /**
     * 构造方法,传入预期的最大index.
     */
    public BitMapTest(int size) {
        this.data = new int[size >> 5];
    }

    /**
     * get 方法, 传入要获取的index, 返回bool值代表该位上为1/0
     */
    public boolean get(int bitIdx) {
        return (data[bitIdxToWorkIdx(bitIdx)] & (1 << bitIdx)) != 0;
    }

    /**
     * 将对应位置的值设置为传入的bool值
     */
    public void set(int idx, boolean v) {
        if (v) {
            set(idx);
        } else {
            clear(idx);
        }
    }

    // 将index的值设置为1
    private void set(int idx) {
        data[bitIdxToWorkIdx(idx)] |= 1 << idx;
    }

    // 将index上的值设置为0
    private void clear(int bitIdx) {
        data[bitIdxToWorkIdx(bitIdx)] &= ~(1L << bitIdx);
    }

    // 根据bit的index获取它存储的实际int在数组中的index
    private int bitIdxToWorkIdx(int bitIdx) {
        return bitIdx >> 5;
    }

    public static void main(String[] args) {

        BitMapTest t = new BitMapTest(100);
        t.set(10, true);

        System.out.println(t.get(9));
        System.out.println(t.get(10));

    }
}

    // long数组,64位的long是2的6次方
    private final static int ADDRESS_BITS_PER_WORD = 6;
    // 每一个word的bit数量
    private final static int BITS_PER_WORD = 1 << ADDRESS_BITS_PER_WORD;

    // 存储数据的long数组
    private long[] words;
    // 上面的数组中使用到了的word的个数
    private transient int wordsInUse = 0;
    // 数组的大小是否由用户指定的(注释里写明了:如果是true,我们假设用户知道他自己在干什么)
    private transient boolean sizeIsSticky = false;

    // ---------构造方法-------

    // 无参的构造方法,初始化数组为长度为64个bit(即一个long)以及设置sizeIsSticky为false.
    public BitSet() {
        initWords(BITS_PER_WORD);
        sizeIsSticky = false;
    }

    // 根据用户传入的bit数量进行初始化,且设置sizeIsSticky为true.
    public BitSet(int nbits) {
        // nbits can't be negative; size 0 is OK
        if (nbits < 0)
            throw new NegativeArraySizeException("nbits < 0: " + nbits);

        initWords(nbits);
        sizeIsSticky = true;
    }
    // ---------构造方法的调用链 -------

    // 初始化数组
    private void initWords(int nbits) {
        words = new long[wordIndex(nbits-1) + 1];
    }

    // 根据bit数量获取long数组的大小,右移6位即可.
    private static int wordIndex(int bitIndex) {
        return bitIndex >> ADDRESS_BITS_PER_WORD;
    }

    // ---------工厂方法,返回BitSet实例 -------

    // 传入long数组
    public static BitSet valueOf(long[] longs) {
        int n;
        for (n = longs.length; n > 0 && longs[n - 1] == 0; n--)
            ;
        return new BitSet(Arrays.copyOf(longs, n));
    }

    // 传入LongBuffer
    public static BitSet valueOf(LongBuffer lb) {
        lb = lb.slice();
        int n;
        for (n = lb.remaining(); n > 0 && lb.get(n - 1) == 0; n--)
            ;
        long[] words = new long[n];
        lb.get(words);
        return new BitSet(words);
    }

    // 传入字节数组
    public static BitSet valueOf(byte[] bytes) {
        return BitSet.valueOf(ByteBuffer.wrap(bytes));
    }

    // 传入ByteBuffer
    public static BitSet valueOf(ByteBuffer bb) {
        bb = bb.slice().order(ByteOrder.LITTLE_ENDIAN);
        int n;
        for (n = bb.remaining(); n > 0 && bb.get(n - 1) == 0; n--)
            ;
        long[] words = new long[(n + 7) / 8];
        bb.limit(n);
        int i = 0;
        while (bb.remaining() >= 8)
            words[i++] = bb.getLong();
        for (int remaining = bb.remaining(), j = 0; j < remaining; j++)
            words[i] |= (bb.get() & 0xffL) << (8 * j);
        return new BitSet(words);
    }

   // 将某个index的值设置为true. 使用和上面自己实现的简陋版本相同的或操作.
    public void set(int bitIndex) {
        if (bitIndex < 0)
            throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex);

        int wordIndex = wordIndex(bitIndex);
        expandTo(wordIndex);

        words[wordIndex] |= (1L << bitIndex); // Restores invariants

        checkInvariants();
    }

    // 将某个index设置为传入的值,注意当传入值为false的时候,调用的是clear方法.
    public void set(int bitIndex, boolean value) {
        if (value)
            set(bitIndex);
        else
            clear(bitIndex);
    }

    // 将index上bit置为0
    public void clear(int bitIndex) {
        if (bitIndex < 0)
            throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex);

        int wordIndex = wordIndex(bitIndex);
        if (wordIndex >= wordsInUse)
            return;

        words[wordIndex] &= ~(1L << bitIndex);

        recalculateWordsInUse();
        checkInvariants();
    }

    // 将from->to之间的所有值设置为true
    public void set(int fromIndex, int toIndex) {
        checkRange(fromIndex, toIndex);

        if (fromIndex == toIndex)
            return;
        // Increase capacity if necessary
        int startWordIndex = wordIndex(fromIndex);
        int endWordIndex   = wordIndex(toIndex - 1);
        expandTo(endWordIndex);

        long firstWordMask = WORD_MASK << fromIndex;
        long lastWordMask  = WORD_MASK >>> -toIndex;
        if (startWordIndex == endWordIndex) {
            // Case 1: One word
            words[startWordIndex] |= (firstWordMask & lastWordMask);
        } else {
            // Case 2: Multiple words
            // Handle first word
            words[startWordIndex] |= firstWordMask;

            // Handle intermediate words, if any
            for (int i = startWordIndex+1; i < endWordIndex; i++)
                words[i] = WORD_MASK;

            // Handle last word (restores invariants)
            words[endWordIndex] |= lastWordMask;
        }

        checkInvariants();
    }

    // 将from->to之间的所有值设置为传入的值,当传入的值为false的适合,调用的是下面的clear.
    public void set(int fromIndex, int toIndex, boolean value) {
        if (value)
            set(fromIndex, toIndex);
        else
            clear(fromIndex, toIndex);
    }

    // 将范围内的bit置为0
    public void clear(int fromIndex, int toIndex) {
        checkRange(fromIndex, toIndex);

        if (fromIndex == toIndex)
            return;

        int startWordIndex = wordIndex(fromIndex);
        if (startWordIndex >= wordsInUse)
            return;

        int endWordIndex = wordIndex(toIndex - 1);
        if (endWordIndex >= wordsInUse) {
            toIndex = length();
            endWordIndex = wordsInUse - 1;
        }

        long firstWordMask = WORD_MASK << fromIndex;
        long lastWordMask  = WORD_MASK >>> -toIndex;
        if (startWordIndex == endWordIndex) {
            // Case 1: One word
            words[startWordIndex] &= ~(firstWordMask & lastWordMask);
        } else {
            // Case 2: Multiple words
            // Handle first word
            words[startWordIndex] &= ~firstWordMask;

            // Handle intermediate words, if any
            for (int i = startWordIndex+1; i < endWordIndex; i++)
                words[i] = 0;

            // Handle last word
            words[endWordIndex] &= ~lastWordMask;
        }

        recalculateWordsInUse();
        checkInvariants();
    }

    // 获取某个位置的bit值
    public boolean get(int bitIndex) {
        if (bitIndex < 0)
            throw new IndexOutOfBoundsException("bitIndex < 0: " + bitIndex);

        checkInvariants();

        int wordIndex = wordIndex(bitIndex);
        return (wordIndex < wordsInUse)
            && ((words[wordIndex] & (1L << bitIndex)) != 0);
    }

    // 返回一个子集,包含传入范围内的bit
    public BitSet get(int fromIndex, int toIndex) {
        checkRange(fromIndex, toIndex);

        checkInvariants();

        int len = length();

        // If no set bits in range return empty bitset
        if (len <= fromIndex || fromIndex == toIndex)
            return new BitSet(0);

        // An optimization
        if (toIndex > len)
            toIndex = len;

        BitSet result = new BitSet(toIndex - fromIndex);
        int targetWords = wordIndex(toIndex - fromIndex - 1) + 1;
        int sourceIndex = wordIndex(fromIndex);
        boolean wordAligned = ((fromIndex & BIT_INDEX_MASK) == 0);

        // Process all words but the last word
        for (int i = 0; i < targetWords - 1; i++, sourceIndex++)
            result.words[i] = wordAligned ? words[sourceIndex] :
                (words[sourceIndex] >>> fromIndex) |
                (words[sourceIndex+1] << -fromIndex);

        // Process the last word
        long lastWordMask = WORD_MASK >>> -toIndex;
        result.words[targetWords - 1] =
            ((toIndex-1) & BIT_INDEX_MASK) < (fromIndex & BIT_INDEX_MASK)
            ? /* straddles source words */
            ((words[sourceIndex] >>> fromIndex) |
             (words[sourceIndex+1] & lastWordMask) << -fromIndex)
            :
            ((words[sourceIndex] & lastWordMask) >>> fromIndex);

        // Set wordsInUse correctly
        result.wordsInUse = targetWords;
        result.recalculateWordsInUse();
        result.checkInvariants();

        return result;
    }

    // 与操作
    public void and(BitSet set);
    // 或操作
    public void or(BitSet set);
    // 异或操作
    public void xor(BitSet set);
    // 与非操作
    public void andNot(BitSet set);

BITOP AND destkey srckey1 srckey2 srckey3 ... srckeyN
BITOP OR destkey srckey1 srckey2 srckey3 ... srckeyN
BITOP XOR destkey srckey1 srckey2 srckey3 ... srckeyN
BITOP NOT destkey srckey