Java基础：HashMap中putAll方法的疑惑

@Override
public void putAll(Map<? extends K, ? extends V> m) {
int numKeysToBeAdded = m.size();
if (numKeysToBeAdded == 0)
return;
// TODO 这里的numKeysToBeAdded是不是应该要this.size+m.size()呢？
// TODO 这里确实有点问题，下面的for循环中put操作可能会导致再次resize，奇怪怎么没人提出这个问题呢？
if (numKeysToBeAdded > threshold) {
// +1是为了补上被强转为int而抹去的小数部分
int targetCapacity = (int)(numKeysToBeAdded / loadFactor + 1);
if (targetCapacity > MAXIMUM_CAPACITY)
targetCapacity = MAXIMUM_CAPACITY;
int newCapacity = table.length;
while (newCapacity < targetCapacity)
newCapacity <<= 1;
if (newCapacity > table.length)
resize(newCapacity);
} for (Map.Entry<? extends K, ? extends V> e : m.entrySet())
put(e.getKey(), e.getValue());
}

Map map = new HashMap(4);
Map m = new HashMap(8);
map.put("a", "haha");
map.put("b", "haha");
map.put("c", "haha");
m.put("1", "a");
m.put("2", "a");
m.put("3", "a");
m.put("4", "a");
map.putAll(m);

/*
* Expand the map if the map if the number of mappings to be added
* is greater than or equal to threshold. This is conservative; the
* obvious condition is (m.size() + size) >= threshold, but this
* condition could result in a map with twice the appropriate capacity,
* if the keys to be added overlap with the keys already in this map.
* By using the conservative calculation, we subject ourself
* to at most one extra resize.
*/