ArrayList is suitable for random access and memory-sensitive scenarios, while LinkedList is suitable for frequent insertion and deletion operations. ArrayList is implemented based on array, with a complexity of get operation O(1), suitable for use when frequently read or large data volume; LinkedList is a linked list structure, with complexity of insertion and deletion O(1), but attention should be paid to the time-consuming positioning, and is suitable for header or existing node operations; in terms of memory, ArrayList is more compact, and the expansion mechanism brings stable access speed, while each node of LinkedList takes up two additional pointer space; when actually choosing, weighing the advantages and disadvantages according to the specific scenario.

Java's ArrayList and LinkedList are both commonly used List implementation classes, but they have their own emphasis on performance. If you pay attention to program efficiency, especially scenarios where data volume is large or frequent operation, it is particularly important to choose the right collection type.

Random access: ArrayList Faster

The ArrayList underlying layer is implemented based on arrays, so it supports quick access to arbitrary elements through indexes. This structure makes its get operation time complexity O(1), which is very efficient.

LinkedList is a linked list structure. Each time, you need to traverse from the beginning or end until the target node is found, with an average time complexity of O(n). Therefore, if your application often needs to obtain elements based on the index, such as looping traversal and frequently reading data at the middle position, it is more appropriate to use ArrayList .

For example:

• A list of millions of data, ArrayList responds significantly faster if you want to read values ??from different locations repeatedly.
• If it is just sequential access, the difference between the two is not so obvious.

Insert and Delete: LinkedList has more advantages

The advantages of LinkedList are reflected when elements are frequently inserted and deleted in the middle or head.

Because ArrayList uses array storage, insertion or deletion will cause all subsequent elements to move positions, the time complexity is O(n). LinkedList only needs to modify the pointer of the adjacent node, and the time complexity of insertion/deletion is O(1) (provided that the location has been found).

But one thing to note:

• LinkedList Although insertion is fast, positioning the insertion position is slow . If you call list.add(index, element), the underlying layer still needs to traverse to that location first, and this part takes O(n).
• So LinkedList really reflects performance advantages only if you insert (addFirst/addLast) in the head or tail, or already have node references.

Memory occupancy and capacity expansion mechanism

ArrayList will allocate a continuous piece of memory space when initialized, and will automatically expand when the capacity is insufficient (the default growth is 50%). Although expansion will bring some overhead, it is exchanged for a more stable access speed.

LinkedList Each element is an independent object (Node). In addition to saving data, each node also needs to save references to the front and rear nodes. This means:

• Each element has two additional pointers for space overhead
• The overall memory usage is much larger than ArrayList

So if you are more sensitive to memory or have a very large amount of data, give priority to ArrayList .

Practical usage suggestions

So when should I use which one? Here are a few reference points:

• Need frequent access to elements? Choose ArrayList
• Often insert/delete in the head or middle? Select LinkedList
• Not much data? The performance differences between the two can be ignored
• Memory tight? ArrayList saves more space
• Used as a queue? You can use LinkedList or recommend ArrayDeque

Basically these differences. After understanding their respective advantages and disadvantages, you can make reasonable choices based on the specific scenario.

The above is the detailed content of Analyzing Java ArrayList and LinkedList Performance Characteristics. For more information, please follow other related articles on the PHP Chinese website!