在Java中選擇ArrayList還是LinkedList取決於使用場景。 1.當(dāng)頻繁通過索引訪問元素時，應(yīng)選擇ArrayList，因其基於動態(tài)數(shù)組實現(xiàn)，支持O(1)時間複雜度的快速隨機訪問；2.當(dāng)頻繁進行中間插入或刪除操作時，應(yīng)選擇LinkedList，因其基於雙向鍊錶實現(xiàn)，支持O(1)時間複雜度的操作（若已有節(jié)點引用）；3.內(nèi)存方面，ArrayList更緊湊，而LinkedList因存儲額外指針導(dǎo)致更高內(nèi)存開銷；4.兩者迭代性能相近，但ArrayList更適合重複get(i)的遍歷方式。因此根據(jù)具體需求選擇合適的數(shù)據(jù)結(jié)構(gòu)。

In Java, both ArrayList and LinkedList are commonly used to store collections of objects, but they work differently under the hood and perform better in different scenarios. The main difference lies in their internal structure: ArrayList is based on a dynamic array, while LinkedList uses a doubly-linked list.

If you're choosing between them, it's important to understand how each affects performance for operations like adding, removing, or accessing elements.

When Access Speed Matters: ArrayList Wins

If your code needs to frequently retrieve elements by index — say, using get(index) — then ArrayList is usually the better choice. Why? Because it stores elements in contiguous memory locations, so accessing an element at any position takes constant time ( O(1) ).

For example:

 List<String> list = new ArrayList<>();
list.add("A");
list.add("B");
list.add("C");

String secondItem = list.get(1); // Fast access

This makes ArrayList ideal for situations where you read more than you modify.

However, if you're inserting or deleting elements from the middle of the list often, especially with large datasets, this can be slower because the underlying array may need to be resized or shifted.

When Modifying Often: LinkedList Can Be Better

On the flip side, if your application does a lot of insertions or deletions — especially in the middle of the list — LinkedList can outperform ArrayList . That's because those operations only require updating a few pointers in the linked nodes, not shifting large chunks of data.

For instance:

 List<String> list = new LinkedList<>();
list.add("A");
list.add("B");
list.add("C");

list.add(1, "X"); // Inserting in the middle

This kind of operation runs in O(1) time if you already have a reference to the node (like when iterating with a ListIterator ). But if you don't, you still need to traverse the list to find the right spot, which takes linear time ( O(n) ).

Also, LinkedList has built-in support for efficient add/remove operations at both ends, offering methods like addFirst() and addLast() .

Memory Overhead and Practical Considerations

Another thing to consider is memory usage. Each node in a LinkedList contains not just the element value, but also references to the next and previous nodes. This extra overhead means that LinkedList typically uses more memory than an ArrayList of the same size.

Here's a quick comparison:

• ArrayList : More compact, good for mostly reading and occasional updates.
• LinkedList : Higher memory footprint, better for frequent insertions and deletions.

Also, keep in mind:

• Iterating through both lists is generally similar in performance.
• ArrayList supports random-access efficiently; LinkedList doesn't.
• If you're using a loop that calls get(i) repeatedly, ArrayList will feel much smoother.

So, choosing between ArrayList and LinkedList really depends on what your program does most. It's not about one being universally better — it's about matching the data structure to your use case.

基本上就這些。

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