There is a performance bug in HashMap.putAll. The logic to pre-expand
the array is not correct. The code might cause the array to be
expanded twice instead of once, for example when
        threshold = 8
        size = 7
        t.size() = 15
        loadFactor = 1

The correction is to add the line
        n += size;
after the lines
        if (n == 0)
            return;