hashmap分解大法--tableSizeFor方法

/**
 * 根据容量参数，返回一个2的n次幂的table长度。
 */
private static final int tableSizeFor(int c) {
    int n = c - 1;
    n |= n >>> 1;
    n |= n >>> 2;
    n |= n >>> 4;
    n |= n >>> 8;
    n |= n >>> 16;
    return (n < 0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1;
}

public static void main(String[] args) {
    System.out.println(tableSizeFor(1));
    System.out.println(tableSizeFor(7));
    System.out.println(tableSizeFor(29));
    System.out.println(tableSizeFor(122));
    System.out.println(tableSizeFor(789));
}

输出：
1
8
32
128
1024