HashMap扩容的这一步怎么理解

[天涯with0]

这一步的扩容阈值不应该是数组长度*加载因子吗？为什么非得当前数组长度<default_inital_capacity时扩容阈值才等于长度*加载因子呢

[imiMi_]

看这个图有些细节是看不懂的，建议看源码，这部分的源码我给你贴这儿了，这是jdk1.8的扩容逻辑 int oldCap = (oldTab == null) ? 0 : oldTab.length; int oldThr = threshold; int newCap, newThr = 0; if (oldCap > 0) { if (oldCap >= MAXIMUM_CAPACITY) { threshold = Integer.MAX_VALUE; return oldTab; } else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY && oldCap >= DEFAULT_INITIAL_CAPACITY) newThr = oldThr << 1; // double threshold } else if (oldThr > 0) // initial capacity was placed in threshold newCap = oldThr; else { // zero initial threshold signifies using defaults newCap = DEFAULT_INITIAL_CAPACITY; newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY); } if (newThr == 0) { float ft = (float)newCap * loadFactor; newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ? (int)ft : Integer.MAX_VALUE); } threshold = newThr;

[一个帅逼]

你这文档看着应该就是jdk1.8的hashMap，但是好像有点问题，看源码是如果你重载了负载因子和底层初始化数组长度，数组扩容时，按你说的情况会走到图中圈起来的部分，新数组的扩容阈值会等于当前数组长度*2*负载因子