关于java:JDK7ConcurentHashMap

public ConcurrentHashMap(int initialCapacity,
 float loadFactor, int concurrencyLevel) {
        int sshift = 0;
        int ssize = 1;
        //找到一个大于或等于concurrencyLevel 的一个
        //2的幂次方数
        while (ssize < concurrencyLevel) {
            ++sshift;
            ssize <<= 1;
        }
        //前面用于取hashcode的高位进行运算
        this.segmentShift = 32 - sshift;
        this.segmentMask = ssize - 1;
        if (initialCapacity > MAXIMUM_CAPACITY)
            initialCapacity = MAXIMUM_CAPACITY;
        //确定HahsEntry数组的长度
        int c = initialCapacity / ssize;
        //下面除可能造成了“向下取整”，而这里要“向上取整”
        //所以进行以下判断进行+1
        if (c * ssize < initialCapacity)
            ++c;
        //MIN_SEGMENT_TABLE_CAPACITY 默认为2，
        //即HashEntry数组最小长度为2
        int cap = MIN_SEGMENT_TABLE_CAPACITY;
        //这里同样是找一个大于等于c的一个2的幂次方数
        //cap就是HashEntry对象的容量
        while (cap < c)
            cap <<= 1;
        // create segments and segments[0]
        //创立一个Segment s0对象寄存在Segment数组下标为0的
        //地位，便于前面寄存元素不必再从新计算HahsEntry
        //的容量等属性(原型设计思维)
        Segment<K,V> s0 =
            new Segment<K,V>(loadFactor, (int)(cap * loadFactor),
                             (HashEntry<K,V>[])new HashEntry[cap]);
        Segment<K,V>[] ss = (Segment<K,V>[])new Segment[ssize];
        //将s0写入ss数组地址为SBASE的地位（就是下标为0）
        UNSAFE.putOrderedObject(ss, SBASE, s0); // ordered write of segments[0]
        this.segments = ss;
    }