A brief introduction to the usage and differences of arrays, ArrayList, List, and Dictionary in C#

I often encounter C# array, ArrayList, List, and Dictionary to access data, but which one should I choose? What type of data is stored? I'm very confused. Today, I took the time to sort out the content for you. Friends who need it can refer to it

Preface

At work I often encounter C# arrays, ArrayList, List, and Dictionary to access data, but as a beginner, I never know which type to choose to store data. So I took the time to take a closer look at their usage and comparison, and summarized it here. I will update it later if there are any improvements that need to be made.

Initialization

Array:

int[] buff = new int[6];

ArrayList:

ArrayList buff = new ArrayList();

List：

List<int> buff = new List<int>();

Dictionary：

Dictionary<int,string> buff = new Dictionary<int,string>;

Analysis and comparison

It can be seen from the several types initialized above that they all belong to the reference type. Among them, arrays, Lists, and Dictionaries need to specify their element types when initializing, while ArrayList does not need to specify the type. And in it only the array has its size set during initialization.

Array: Its size and type must be specified during initialization. It is stored continuously in memory, so it can be seen that the indexing speed of the array is very fast. After determining the length and type of the array, it is a better choice to choose an array to store data. Not suitable for insert operations.

　ArrayList: There is no need to specify its size and type during initialization. It can store different data types, but it will cause boxing and unboxing during the storage and retrieval process, which reduces performance. Easy to insert.

List: Its type must be specified during initialization, but the size does not need to be specified, so it will not cause boxing and unboxing operations during the access process like ArraryList. In the case of the same type, the performance of List and array is equivalent. Easy to insert.

　Dictionary: Its type must also be specified during initialization, and it also needs to specify a Key, and this Key is unique. Because of this, Dictionary indexing is very fast. But also because it adds a Key, Dictionary takes up more memory space than other types. It searches for elements through Key, and the order of the elements is uncertain.

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