为什么在HashMap中为getEntry定义对象 [英] Why define object for getEntry in HashMap
问题描述
我是新来的泛型,我不知道我的问题的答案是
I am new to generics and I am not sure if the answer to my question is opinion based
or has a genuine reason. In the following code what was need to case a key of an entry to an object ?
Object k;
if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
它似乎很容易被替换为
It appears to be easily replaced by
if (e.hash == hash && (e.key == key || (key != null && key.equals(e.key))))
更多参考资料:
More reference:
final Entry<K,V> getEntry(Object key) {
int hash = (key == null) ? 0 : hash(key);
for (Entry<K,V> e = table[indexFor(hash, table.length)];
e != null;
e = e.next) {
Object k;
if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k))))
return e;
}
return null;
}
推荐答案
这是一种极端的优化措施这对于通用编程实践可能不是必需的。这是一个可以回答的讨论你的问题。下面的语句是从该文章复制的:
This is an extreme optimization measure that is probably not necessary for general purpose programming practice. Here is a discussion that could answer your question. Below statement is copied from that post:
这是由Doug Lea广受欢迎的编码风格。这是一种极端的优化,可能没有必要;您可以期待JIT进行相同的优化。 (你可以尝试自己检查机器代码!)尽管如此,复制到本地机器生成最小的字节码,对于低级代码,编写代码更接近机器是很好的。
It's a coding style made popular by Doug Lea. It's an extreme optimization that probably isn't necessary; you can expect the JIT to make the same optimizations. (you can try to check the machine code yourself!) Nevertheless, copying to locals produces the smallest bytecode, and for low-level code it's nice to write code that's a little closer to the machine.
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