Array sort 2

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Sort for classes , First of all, we should realize  IComparable Interface . It defines a general type specific comparison method , Value types or classes sort their instances by implementing this method .

The following is a student class , Only student ID is included id（Integer） And name name（String）. Ensure that this class implements IComparable Interface , And implemented CompareTo Method ：

Public Class student
    Implements IComparable(Of student)

    Public Function CompareTo(other As student) As Integer Implements IComparable(Of student).CompareTo
       ……
    End Function

The specific code is as follows

Public Class student
    Implements IComparable(Of student)

    Public Property id As Integer
    Public Property Name As String

    Sub New(ByVal id As Integer, ByVal Name As String)
        Me.id = id
        Me.Name = Name
    End Sub

    Public Function CompareTo(other As student) As Integer Implements IComparable(Of student).CompareTo
        Return id.CompareTo(other.id)
    End Function

    Public Overrides Function ToString() As String
        Return id & ":" & Name
    End Function
End Class

The code uses Integer Of CompareTo Method .
Because it involves the following output , It also rewrites ToString Method , according to “ Student number ： full name ” Mode output of .

Sub Main Use in Student The code for the class is as follows ：

        Dim teststudent() As student = New student() {
                                      New student(12, "Bolger"),
                                      New student(13, "Quin"),
                                      New student(11, "Anie"),
                                      New student(10, "Besterman"),
                                      New student(14, "Orvis")
                                      }
        Console.WriteLine(" Sort by student number ：")
        Dim copystudent1() As student
        copystudent1 = teststudent.Clone
        Array.Sort(copystudent1)
        For i As Integer = 0 To copystudent1.Length - 1
            Console.WriteLine(copystudent1(i).ToString & " ")
        Next
        Console.WriteLine()

        Console.WriteLine(" In reverse order of student number ：")
        Dim copystudent2() As student
        copystudent2 = teststudent.Clone
        Array.Sort(copystudent2)
        Array.Reverse(copystudent2)
        For i As Integer = 0 To copystudent2.Length - 1
            Console.WriteLine(copystudent2(i).ToString & " ")
        Next
        Console.WriteLine()

        Console.WriteLine(" Original array ：")
        Dim copystudent3() As student
        copystudent3 = teststudent.Clone
        Array.Sort(copystudent3, AddressOf Comparison)
        For i As Integer = 0 To copystudent3.Length - 1
            Console.WriteLine(copystudent3(i).ToString & " ")
        Next
        Console.WriteLine()
        Console.ReadKey()

Run as shown in the figure below ：

In the above code, the implementation of id Sort , What if you sort by name ？
Do not add code in the class , Add the following code to the module , Use names for comparison ：

    Private Function Comparison(x As student, y As student) As Integer
        Return (x.Name).CompareTo(y.Name)
    End Function

Sub Main Add code to ：

        Console.WriteLine(" Sort by name ：")
        Dim copystudent3() As student
        copystudent3 = teststudent.Clone
        Array.Sort(copystudent3, AddressOf Comparison)
        For i As Integer = 0 To copystudent3.Length - 1
            Console.WriteLine(copystudent3(i).ToString & " ")
        Next
        Console.WriteLine()
        Console.ReadKey()
        Exit Sub

  The operation results are as follows ：

What we use here is Array Of Public Shared Sub Sort(Of T) ( array As T(),  comparison As Comparison(Of T) ) Method , Using the Comparison(Of T) entrust , Use the following statement ：
Public Delegate Function Comparison(Of In T) ( _
    x As T, _
    y As T _
) As Integer
The simplified method of use is directly in Sort() Method used in   Addressof  Method name .

If the return value of this delegate method is less than 0, that x be ranked at y front . The above code is simple to use String Of CompareTo Method .

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