java利用数组和位运算构建bitmap

java利用数组和位运算构建bitmap

public class BitMap {
    private char[] bytes;
    
    private int nbits;

    public BitMap(int nbits) {
        this.nbits = nbits;
        this.bytes = new char[nbits / 16 + 1];
    }

    public void set(int k) {
        if (k > nbits) {
            return;
        }
        int byteIndex = k / 16;
        int bitIndex = k % 16;
        bytes[byteIndex] |= (1 << bitIndex);
    }

    public boolean get(int k) {
        if (k > nbits) {
            return false;
        }
        int byteIndex = k / 16;
        int bitIndex = k % 16;
        return (bytes[byteIndex] & (1 << bitIndex)) != 0;
    }
}

为了让人更好的理解位运算请看以下小例子

System.out.println(Integer.toBinaryString(1<<1));
System.out.println(Integer.toBinaryString(1<<2));
char a = 1<<1;
a |= 1<<2;
System.out.println(Integer.toBinaryString(a ));

输出结果为

10
100
110