如何处理GetHashCode
函数中的空字段?
Module Module1
Sub Main()
Dim c As New Contact
Dim hash = c.GetHashCode
End Sub
Public Class Contact : Implements IEquatable(Of Contact)
Public Name As String
Public Address As String
Public Overloads Function Equals(ByVal other As Contact) As Boolean _
Implements System.IEquatable(Of Contact).Equals
Return Name = other.Name AndAlso Address = other.Address
End Function
Public Overrides Function Equals(ByVal obj As Object) As Boolean
If ReferenceEquals(Me, obj) Then Return True
If TypeOf obj Is Contact Then
Return Equals(DirectCast(obj, Contact))
Else
Return False
End If
End Function
Public Overrides Function GetHashCode() As Integer
Return Name.GetHashCode Xor Address.GetHashCode
End Function
End Class
End Module
答案 0 :(得分:32)
通常,如果字段为空,则检查null并对哈希码的“部分”使用0:
return (Name == null ? 0 : Name.GetHashCode()) ^
(Address == null ? 0 : Address.GetHashCode());
(原谅C#-ism,不确定VB中的null check等价物)
答案 1 :(得分:6)
正如Jeff Yates所建议的那样,答案中的覆盖将为(name = null,address =“foo”)提供相同的哈希值(name =“foo”,address = null)。这些需要不同。如链接中所示,类似于以下内容会更好。
public override int GetHashCode()
{
unchecked // Overflow is fine, just wrap
{
int hash = 17;
hash = hash * 23 + (Name == null ? 0 : Name.GetHashCode());
hash = hash * 23 + (Address == null ? 0 : Address.GetHashCode());
}
return hash;
}
What is the best algorithm for an overridden System.Object.GetHashCode?