java - tailmap 方法如何从输入 treemap 中获取 sortedmap？

Question

treemap 有一个方法tailmap 来获取一个sortedmap，它的key 不小于fromkey。跟踪源码发现tailmap在NavigableSubMap的construct方法中完成了工作。这是代码。

NavigableSubMap(TreeMap<K,V> m,
                        boolean fromStart, K lo, boolean loInclusive,
                        boolean toEnd,     K hi, boolean hiInclusive) {
            if (!fromStart && !toEnd) {
                if (m.compare(lo, hi) > 0)
                    throw new IllegalArgumentException("fromKey > toKey");
            } else {
                if (!fromStart) // type check
                    m.compare(lo, lo);
                if (!toEnd)
                    m.compare(hi, hi);
            }

            this.m = m;
            this.fromStart = fromStart;
            this.lo = lo;
            this.loInclusive = loInclusive;
            this.toEnd = toEnd;
            this.hi = hi;
            this.hiInclusive = hiInclusive;
        }

在 this.toEnd = toEnd 的步骤之后；NavigableSubMap 类有尾地图。它是如何完成的？