' Fig. 9.4: LINQWithArrayOfObjects.vb

' LINQ to Objects using an array of Employee objects.

Module LINQWithArrayOfObjects

   Sub Main()

      ' initialize array of employees

      Dim employees As Employee() = { _

         New Employee("Jason", "Red", 5000D), _

         New Employee("Ashley", "Green", 7600D), _

         New Employee("Matthew", "Indigo", 3587.5D), _

         New Employee("James", "Indigo", 4700.77D), _

         New Employee("Luke", "Indigo", 6200D), _

         New Employee("Jason", "Blue", 3200D), _

         New Employee("Wendy", "Brown", 4236.4D)} ' end initializer list

      Display(employees, "Original array") ' display all employees

        ' filter a range of salaries using AndAlso in a LINQ query

        Dim between4K6K = _

           From e In employees _

           Where e.MonthlySalary >= 4000D AndAlso e.MonthlySalary <= 6000D _

           Select e

        ' display employees making between 4000 and 6000 per month

        Display(between4K6K, String.Format( _

           "Employees earning in the range {0:C}-{1:C} per month", _

           4000, 6000))

        ' order the employees by last name, then first name with LINQ

        Dim nameSorted = _

           From e In employees _

           Order By e.LastName, e.FirstName _

           Select e

        Console.WriteLine("First employee when sorted by name:") ' header

        ' attempt to display the first result of the above LINQ query

        If nameSorted.Count() = 0 Then

            Console.WriteLine("not found" & vbNewLine)

        Else

            Console.WriteLine(nameSorted.First().ToString() & vbNewLine)

        End If

        ' use LINQ's Distinct clause to select unique last names

        Dim lastNames = _

           From e In employees _

           Select e.LastName _

           Distinct

        ' display unique last names

        Display(lastNames, "Unique employee last names")

        ' use LINQ to select first and last names

        Dim names = _

           From e In employees _

           Select e.FirstName, Last = e.LastName

        Display(names, "Names only") ' display full names

    End Sub ' Main

    ' display a sequence of any type, each on a separate line

    Sub Display(Of T)(ByVal results As IEnumerable(Of T), ByVal header As String)

        Console.WriteLine("{0}:", header) ' display header

        ' display each element, separated by spaces

        For Each element As T In results

            Console.WriteLine(element)

        Next

        Console.WriteLine() ' add end of line

    End Sub ' Display

End Module ' LINQWithArrayOfObjects

' **************************************************************************

' * (C) Copyright 1992-2009 by Deitel & Associates, Inc. and               *

' * Pearson Education, Inc. All Rights Reserved.                           *

' *                                                                        *

' * DISCLAIMER: The authors and publisher of this book have used their     *

' * best efforts in preparing the book. These efforts include the          *

' * development, research, and testing of the theories and programs        *

' * to determine their effectiveness. The authors and publisher make       *

' * no warranty of any kind, expressed or implied, with regard to these    *

' * programs or to the documentation contained in these books. The authors *

' * and publisher shall not be liable in any event for incidental or       *

' * consequential damages in connection with, or arising out of, the       *

' * furnishing, performance, or use of these programs.                     *

' **************************************************************************

' Fig. 9.3: Employee.vb

' Employee class with FirstName, LastName and MonthlySalary properties.

Public Class Employee

   Private firstNameValue As String ' first name of employee

   Private lastNameValue As String ' last name of employee

   Private monthlySalaryValue As Decimal ' monthly salary of employee

   ' constructor initializes first name, last name and monthly salary

    Public Sub New(ByVal first As String, ByVal last As String, ByVal salary As Decimal)

        FirstName = first

        LastName = last

        MonthlySalary = salary

    End Sub ' New

   ' property that gets and sets the employee's first name

   Public Property FirstName() As String

      Get

         Return firstNameValue

      End Get

      Set(ByVal value As String)

         firstNameValue = value

      End Set

   End Property ' FirstName

   ' property that gets and sets the employee's last name

   Public Property LastName() As String

      Get

         Return lastNameValue

      End Get

      Set(ByVal value As String)

         lastNameValue = value

      End Set

   End Property ' LastName

   ' property that gets and sets the employee's monthly salary

   Public Property MonthlySalary() As Decimal

      Get

         Return monthlySalaryValue

      End Get

      Set(ByVal value As Decimal)

            If value >= 0 Then ' if salary is non-negative(非负)

                monthlySalaryValue = value

            End If

      End Set

   End Property ' MonthlySalary

    ' return a String containing the employee's information

    ' left justify each field, and give large enough spaces so  all the columns line up.

    Public Overrides Function ToString() As String

        Return String.Format("{0,-10} {1,-10} {2,10:C}", FirstName, LastName, MonthlySalary)

    End Function ' ToString

End Class ' Employee

' **************************************************************************

' * (C) Copyright 1992-2009 by Deitel & Associates, Inc. and               *

' * Pearson Education, Inc. All Rights Reserved.                           *

' *                                                                        *

' * DISCLAIMER: The authors and publisher of this book have used their     *

' * best efforts in preparing the book. These efforts include the          *

' * development, research, and testing of the theories and programs        *

' * to determine their effectiveness. The authors and publisher make       *

' * no warranty of any kind, expressed or implied, with regard to these    *

' * programs or to the documentation contained in these books. The authors *

' * and publisher shall not be liable in any event for incidental or       *

' * consequential damages in connection with, or arising out of, the       *

' * furnishing, performance, or use of these programs.                     *

' **************************************************************************