使用.GetHashCode（）的对象相等性列表

Question

I would like to understand how the GetHashCode method works on lists of objects for equality. Given this example:

var user1 = new User { Id = Guid.NewGuid().ToString(), Name = "Chris" };
var user2 = new User { Id = Guid.NewGuid().ToString(), Name = "Jeff" };

var userList1 = new List<User> { user1, user2 }.OrderBy(o => o.Id);
var userList2 = new List<User> { user1, user2 }.OrderBy(o => o.Id);

var usersList1Hash = userList1.GetHashCode();
var usersList2Hash = userList2.GetHashCode();

var userListsEqual = usersList1Hash == usersList2Hash; // false

var userList1Json = JsonConvert.SerializeObject(userList1);
var userList2Json = JsonConvert.SerializeObject(userList2);

var usersList1JsonHash = userList1Json.GetHashCode();
var usersList2JsonHash = userList2Json.GetHashCode();

var userListsJsonEqual = usersList1JsonHash == usersList2JsonHash; // true

1. Why are the lists of objects not equal when comparing the hash codes?

2. Why are the list of objects equal when serializing to JSON strings and comparing the hash codes?

Answer 1

GetHashCode function gives signed int32 hash of an object.

From MSDN.

Two objects that are equal return hash codes that are equal. However, the reverse is not true: equal hash codes do not imply object equality, because different (unequal) objects can have identical hash codes.

GetHashCode is a virtual function and can be overridden. What you get after calling JsonConvert.SerializeObject function a string. string class has its own implementation of GetHashCode which is based on contents of a string. Something like below. That's why it matches.

public class string {  
  char[] str = null;
  ...
  public string(char[] input) {
    this.str = input;
  }

  public override GetHashCode() {
    //Logic to convert str to int 32 based on string contents;

    return Convert.ToInt32(str);
  }
}