Talking about:arraylist,list<t>,list<object>

Recently, there's a place in the project where list<object> is used to think that list<object> can dynamically insert object objects, and ArrayList is also dynamically inserting object objects. I wonder if these two functions are the same, look at the meta-data code as follows:

ArrayList

public class Arraylist:ilist, ICollection, IEnumerable, ICloneable

public virtual int Add (object value);//Add an Object

List<t>

public class list<t>: Ilist<t>, Icollection<t>, Ienumerable<t>, IList, ICollection, IEnumerable

public void Add (T item);//Add an Object

Compare the two, found that the Add method of the two is overridable, and return the current index, one is the void method, T item, when T is an object, the individual think that the difference is not big, but they if the add value type when the boxing operation will be triggered, affecting performance, through the test found ( Test code in the attachment), ArrayList and list<object> both perform the same operation, the same efficiency, whether there is no disassembly box. However, if you use list<t>, it is best not to pass T into object, otherwise lose the meaning of generic T. If you perform an int operation, use List<int>.

In general, the process of developing procedures to avoid the operation of the Disassembly box, frequent unpacking will reduce the efficiency of a lot.

Digression: Before looking at the interview topic, asked the difference between ArrayList and list, feel confused, until now understand, originally asked is such a problem, alas, the program can not only write, also have to think Ah, in addition, F12 see program Metadata is also a good learning method. Attached program run result 650) this.width=650; "src=" http://s3.51cto.com/wyfs02/M02/57/1D/wKioL1SSNPGRK6ZNAAEAjzE_B7w360.jpg "title = "QQ picture 20141218095444.png" alt= "wkiol1ssnpgrk6znaaeajze_b7w360.jpg"/>, but biased, if run alone ArrayList or List<object > They two results are not small, but put list<object> in the back of ArrayList run, it will appear slower, there is also a procedural problem, it is here. The above is purely personal opinion, if wrong, please do not hesitate to point out.

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Brief introduction: Arraylist,list<t>,list<object>