英文:
What does this mean? Entry<K,V> e = table[bucketIndex];
问题
我正在研究HashMap内部的工作原理，但无法理解这个方法：
void addEntry(int hash, K key, V value, int bucketIndex) {
Entry<K,V> e = table[bucketIndex];
table[bucketIndex] = new Entry<K,V>(hash, key, value, e);
if (size++ >= threshold)
resize(2 * table.length);
}
为什么对象**e**获得了table[bucketIndex]的地址（或者这里发生了什么？），然后table[bucketIndex]得到了新的<code>Entry<K,V>(hash, key, value, e)。为什么不直接使用下面的内容呢？
Entry<K,V> e = new Entry<K,V>(hash, key, value)
table[bucketIndex] = e;
英文:
I am studying how HashMap works inside and can not understand this method:
> void addEntry(int hash, K key, V value, int bucketIndex) {
> Entry<K,V> e = table[bucketIndex];
> table[bucketIndex] = new Entry<K,V>(hash, key, value, e);
> if (size++ >= threshold)
> resize(2 * table.length);
Why object e gets the address (or what happens here?) of table[bucketIndex] and then this table[bucketIndex] get the new <code>Entry<K,V>(hash, key, value, e)</code>? What is the reason, why didn't just use what is below?
Entry<K,V> e = new Entry<K,V>(hash, key, value)
table[bucketIndex] = e;
答案1
得分: 2
因为在HashMap中可能会发生冲突（即产生相同的bucketIndex的不同键）。如果按照你提出的建议去做，那么在发生冲突的情况下，最后插入的元素将以一种几乎不可预测的方式删除先前的元素。
Entry被实现为一种链表，因此它实际上被命名得有些不准确，实际上它是条目链表的一个节点。这就是为什么在Entry构造函数中将e作为最后一个参数传递的原因。
创建一个引用先前条目（e）的新Entry，并将其添加到与e相同的位置，就是在链表开头插入新节点的操作，即使e为null（即根本没有发生冲突，而创建的Entry是具有给定bucketIndex的第一个条目）。
英文:
Because there could be collisions in the HashMap (i.e. different keys which produces the same bucketIndex). If they did what you suggests, in the case of a collision, the last inserted element would delete the previous ones in the case of a collision, possibly in a virtually unpredictable manner.
The Entry is implemented as some sort of linked list, so it is actually a bit misnamed and is in fact a node of linked list of entries. This is the reason why e is passed as the last parameter of Entry constructor.
Creating a new Entry that refers to the previous one (the e) and adding it in the same place where the e was is the operation of inserting a new node in the beggining of the linked list, and works even if e was null (i.e. there was no collision at all and the created Entry is the first one with the given bucketIndex).
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