java java中链表的poll()和pop()有什么区别？
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whats the difference between poll() and pop() for linkedlist in java?
提问by Mingyaaa
I recently found there are two similar methods for linkedlist in java API, they all delete the first node and return it. I wrote the following codes to test and they did exactly same thing.Do they really work exactly same?
我最近发现java API中有两个类似的链表方法，它们都是删除第一个节点并返回它。我写了下面的代码来测试，他们做了完全一样的事情。他们真的工作完全一样吗？
test.add(1);
test.add(2);
test.add(3);
System.out.println(test.pop());
for(int i = 0; i < test.size();i++ ){
System.out.print(test.get(i) + " ");
}
System.out.println("");
System.out.println(test.poll());
for(int i = 0; i < test.size();i++ ){
System.out.print(test.get(i) + " ");
}
System.out.println("");
Thanks!!!
谢谢！！！
回答by Michal Frystacky
回答by dimo414
They're functionally equivalent (save for how they handle the empty-list case), but you get both variants because LinkedListis an implementation of both a queue and a stack (namely Queueand Deque).
它们在功能上是等效的（除了它们如何处理空列表的情况），但是您会得到两种变体，因为LinkedList是队列和堆栈（即Queue和Deque）的实现。
You can see their implementations in the source code:
你可以在源代码中看到它们的实现：
public E poll() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
public E pop() {
return removeFirst();
}
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
So poll()returns null if the list is empty, and pop()(and removeFirst()) raises a NoSuchElementException. This makes pop()a slightly nicer method to use, since you don't have to deal with nulls.
因此，poll()如果列表为空，则返回 null，并且pop()(and removeFirst()) 引发 a NoSuchElementException。这使得pop()使用稍微好一点的方法，因为您不必处理空值。
