数组排序2

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对于类的排序，首先要实现 IComparable接口。它定义一种特定于类型的通用比较方法，值类型或类通过实现此方法对其实例进行排序。

以下是一个学生类，仅包含学生学号id（Integer）和姓名name（String）。确保该类实现了IComparable接口，并在类里实现了CompareTo方法：

Public Class student
    Implements IComparable(Of student)

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

具体代码如下

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

代码里面默认使用了Integer的CompareTo 方法。
由于涉及后面的输出，这里还重写了ToString方法，按照“学号：姓名”的方式输出。

Sub Main中使用Student类的代码如下：

        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("按照学号排序：")
        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("按照学号倒序：")
        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("原数组：")
        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()

运行如下图所示：

在以上代码中实现了按照id排序，如果以姓名排序呢？
不增加类中的代码，在模块中添加如下代码，使用姓名作比较：

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

Sub Main中增加代码：

        Console.WriteLine("按照姓名排序：")
        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

 运行结果如下图：

这里使用的是Array的Public Shared Sub Sort(Of T) ( array As T(),  comparison As Comparison(Of T) )方法，使用到了Comparison(Of T) 委托，使用如下的声明：
Public Delegate Function Comparison(Of In T) ( _
    x As T, _
    y As T _
) As Integer
简化的使用方法直接在Sort()方法中使用  Addressof  方法名。

该委托方法返回值如果小于 0，那么x排在y前面。上面的代码简单使用了String的CompareTo方法。

由于.net平台下C#和vb.NET很相似，本文也可以为C#爱好者提供参考。

学习更多vb.net知识，请参看vb.net 教程 目录