首先是JDK7的实现，
1 void resize(int newCapacity) { //传入新的容量 2 Entry[] oldTable = table; //引用扩容前的Entry数组 3 int oldCapacity = oldTable.length; 4 if (oldCapacity == MAXIMUM_CAPACITY) { //扩容前的数组大小如果已经达到最大(2^30)了 5 threshold = Integer.MAX_VALUE; //修改阈值为int的最大值(2^31-1)，这样以后就不会扩容了 6 return; 7 } 8 9 Entry[] newTable = new Entry[newCapacity]; //初始化一个新的Entry数组 10 transfer(newTable); //！！将数据转移到新的Entry数组里 11 table = newTable; //HashMap的table属性引用新的Entry数组 12 threshold = (int)(newCapacity * loadFactor);//修改阈值 13 }这里就是使用一个容量更大的数组来代替已有的容量小的数组，transfer()方法将原有Entry数组的元素拷贝到新的Entry数组里。
1 void transfer(Entry[] newTable) { 2 Entry[] src = table; //src引用了旧的Entry数组 3 int newCapacity = newTable.length; 4 for (int j = 0; j < src.length; j++) { //遍历旧的Entry数组 5 Entry<K,V> e = src[j]; //取得旧Entry数组的每个元素 6 if (e != null) { 7 src[j] = null;//释放旧Entry数组的对象引用（for循环后，旧的Entry数组不再引用任何对象） 8 do { 9 Entry<K,V> next = e.next; 10 int i = indexFor(e.hash, newCapacity); //！！重新计算每个元素在数组中的位置 11 e.next = newTable[i]; //标记[1] 12 newTable[i] = e; //将元素放在数组上 13 e = next; //访问下一个Entry链上的元素 14 } while (e != null); 15 } 16 } 17 }newTable[i]的引用赋给了e.next，也就是使用了单链表的头插入方式，同一位置上新元素总会被放在链表的头部位置；这样先放在一个索引上的元素终会被放到Entry链的尾部(如果发生了hash冲突的话），这一点和Jdk1.8有区别。
具体举例如下图所示：
接下来是JDK8中的实现，
/** * Initializes or doubles table size. If null, allocates in * accord with initial capacity target held in field threshold. * Otherwise, because we are using power-of-two expansion, the * elements from each bin must either stay at same index, or move * with a power of two offset in the new table. * * @return the table */ final Node<K,V>[] resize() { Node<K,V>[] oldTab = table; 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; @SuppressWarnings({"rawtypes","unchecked"}) Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap]; table = newTab; if (oldTab != null) { for (int j = 0; j < oldCap; ++j) { Node<K,V> e; if ((e = oldTab[j]) != null) { oldTab[j] = null; if (e.next == null) newTab[e.hash & (newCap - 1)] = e; else if (e instanceof TreeNode) ((TreeNode<K,V>)e).split(this, newTab, j, oldCap); else { // preserve order Node<K,V> loHead = null, loTail = null; Node<K,V> hiHead = null, hiTail = null; Node<K,V> next; do { next = e.next; if ((e.hash & oldCap) == 0) { if (loTail == null) loHead = e; else loTail.next = e; loTail = e; } else { if (hiTail == null) hiHead = e; else hiTail.next = e; hiTail = e; } } while ((e = next) != null); if (loTail != null) { loTail.next = null; newTab[j] = loHead; } if (hiTail != null) { hiTail.next = null; newTab[j + oldCap] = hiHead; } } } } } return newTab; }