Because the LinkedList implements the ICollection interface, it inherits the Contains method. As a reminder, its syntax is: Public Function Contains(value As T) As Boolean This method checks whether the linked list contains the (a) node that has the value passed as argument. If that node is found, the method returns true. Otherwise it returns false. Here is an example of calling it: Public Class Exercise
Private Sub BtnLinkedList_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles BtnLinkedList.Click
Dim Values As List(Of Double) = New List(Of Double)
Values.Add(84.597)
Values.Add(6.47)
Values.Add(2747.06)
Values.Add(282.924)
Dim Numbers As LinkedList(Of Double) = New LinkedList(Of Double)(Values)
Dim Number As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(148.24)
Numbers.AddFirst(number)
number = New LinkedListNode(Of Double)(35.75)
Numbers.AddFirst(number)
number = New LinkedListNode(Of Double)(2222.06)
Numbers.AddFirst(number)
number = New LinkedListNode(Of Double)(4.19)
Numbers.AddFirst(number)
number = New LinkedListNode(Of Double)(66.18)
Numbers.AddFirst(number)
If Numbers.Contains(2222.06) = True Then
MsgBox("The list contains 2222.06.",
MsgBoxStyle.OkOnly Or MsgBoxStyle.Information,
"Linked List")
Else
MsgBox("There is no such a number in the list.",
MsgBoxStyle.OkOnly Or MsgBoxStyle.Information,
"Linked List")
End If
End Sub
End Class
This method works only if the type of the node is able to perform the comparison for equality. If you are using values of primitive types (int, char, double, DateTime, etc) or string, the method would work fine. If you are using your own class, make sure you override the Equals() method.
While the Contains() method is used to look for a value in a linked list, it only lets you know whether the value was found. If you want to get the actual node that has that value, you can call the Find() method. Its syntax is: Public Function Find(value As T) As LinkedListNode(Of T) When this method is called, it starts looking for the value in the linked list. If it finds it, it returns its node. If there is more than one node with that value, the method returns only the first node that has that value. Here is an example of calling this method: Public Class Exercise
Private Sub BtnLinkedList_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles BtnLinkedList.Click
Dim Values As List(Of Double) = New List(Of Double)
Values.Add(84.597)
Values.Add(6.47)
Values.Add(2747.06)
Values.Add(282.924)
Dim Numbers As LinkedList(Of Double) = New LinkedList(Of Double)(Values)
Dim Number As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(148.24)
numbers.AddFirst(Number)
number = New LinkedListNode(Of Double)(35.75)
Numbers.AddFirst(Number)
number = New LinkedListNode(Of Double)(2222.06)
Numbers.AddFirst(Number)
Numbers.AddFirst(2747.06)
number = New LinkedListNode(Of Double)(4.19)
Numbers.AddFirst(Number)
number = New LinkedListNode(Of Double)(66.18)
Numbers.AddFirst(Number)
If Numbers.Find(2747.06) Is Nothing Then
MsgBox("2747.06 was found in the list.",
MsgBoxStyle.OkOnly Or MsgBoxStyle.Information,
"Linked List")
Else
MsgBox("2747.06 is nowhere in the list.",
MsgBoxStyle.OkOnly Or MsgBoxStyle.Information,
"Linked List")
End If
End Sub
End Class
If the list contains more than one node that has the value but you prefer to use the last node, you can call the FindLast() method. Public Function FindLast(value As T) As LinkedListNode(Of T) Once again, remember that these two methods are ready to work on primitive types. If you are using your own class for the type of node, you should (must) override the Equals() method.
As you can see, the LinkedList class doesn't implement the IList interface, which means it doesn't have an Item property. As we have seen with the AddLast() method and as we will see in the next sections, each method used to add a node is provided in two versions. One of the versions returns a LinkedListNode object. This means that, when performing an addition operation, you can get the returned value and do what you want with it. The class LinkedList class implements the IEnumerable interface. This makes it possible to use For Each to get to access each node. This can be done as follows: Public Class Exercise
Private Sub BtnLinkedList_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles BtnLinkedList.Click
Dim Numbers As LinkedList(Of Double) = New LinkedList(Of Double)
Dim Number As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(148.24)
Numbers.AddFirst(Number)
For Each Nbr As Double In Numbers
MsgBox(CStr(Nbr),
MsgBoxStyle.OkOnly Or MsgBoxStyle.Information,
"Linked List")
Next
End Sub
End Class
Probably the most important aspect of a node is its value. To support it, the LinkedListNode class has a property named Value: Public Property Value As T Get Set Because this is a readwrite property, you can use its writeaccessory to specify or change its value. On the other hand, you can access the value of a node using this property.
As mentioned already, a linked list has a first and a last nodes (some people or documentations call them the head and the tail). To identify the first node, the LinkedList class is equippped with a readonly property named First. Its syntax is: Public ReadOnly Property First As LinkedListNode(Of T) Get The last node is represented by a readonly property of the same name and that, too, is a LinkedListNode object: Public ReadOnly Property Last As LinkedListNode(Of T) Get Here are examples of accessing these properties: Public Class Exercise Private Sub BtnLinkedList_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnLinkedList.Click Dim Numbers As LinkedList(Of Double) = New LinkedList(Of Double) Dim Number As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(148.24) Numbers.AddFirst(Number) Number = New LinkedListNode(Of Double)(35.75) Numbers.AddFirst(Number) Number = New LinkedListNode(Of Double)(2222.06) Numbers.AddFirst(Number) Number = New LinkedListNode(Of Double)(4.19) Numbers.AddFirst(Number) Number = New LinkedListNode(Of Double)(66.18) Numbers.AddFirst(Number) MsgBox("The value of the first node is " & Numbers.First.Value, MsgBoxStyle.OkOnly Or MsgBoxStyle.Information, "Linked List") MsgBox("The value of the last node is " & Numbers.Last.Value, MsgBoxStyle.OkOnly Or MsgBoxStyle.Information, "Linked List") End Sub End Class
To access a node that is next to an existing node, you must first know what node is used as reference. To let you access the next node, the LinkedListNode class is equipped with a readonly property named Next: Public ReadOnly Property Next As LinkedListNode(Of T) Get To let you access the node previous to an existing one, the LinkedListNode class is equipped with the readonly Previous property: Public ReadOnly Property Previous As LinkedListNode(Of T) Get Remember that in both cases, you need a node as reference.
When dealing with a linked list, you have many options on how to add a new node. As mentioned already, a linked list has a first node, a last node, and one or more nodes between them. All nodes have and use some references with regards to the node(s) close to them. Based on this, when adding a new node, you have to specify whether you want it as the first node, the last node, the node before a certain node, or the node after a certain one. The LinkedList class easily supports all these operations with very little effort on your part. We saw that you could call the AddFirst() method to add a new node. In reality, there is no such a thing as simply adding a new node to a linked list. When a linked list has just been created and it is empty, it holds a reference to a null node. There is nothing you can do with that node and you don't need to do anything with it. To start adding nodes, you have the option of setting it as the first or the last item. This would not make any difference because there is no other node in the list. After adding a node, it becomes a reference that new nodes can use. If you call the AddFirst() method, the new node would be added before any existing node in the collection.
By contrast, you can call a method named AddLast. It is overloaded with versions whose syntaxes are: Public Function AddLast(value As T) As LinkedListNode(Of T) Public Sub AddLast(node As LinkedListNode(Of T)) When you call this method, the value or node you pass will be added as the last item in the list. Here is an example: Public Class Exercise
Private Sub BtnLinkedList_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles BtnLinkedList.Click
Dim Values As List(Of Double) = New List(Of Double)
Values.Add(84.597)
Values.Add(6.47)
Values.Add(2747.06)
Values.Add(282.924)
Dim Numbers As LinkedList(Of Double) = New LinkedList(Of Double)(Values)
Dim Number As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(148.24)
numbers.AddFirst(Number)
Number = New LinkedListNode(Of Double)(35.75)
numbers.AddFirst(Number)
numbers.AddLast(2747.06)
Number = New LinkedListNode(Of Double)(2222.06)
numbers.AddFirst(Number)
Number = New LinkedListNode(Of Double)(4.19)
numbers.AddFirst(Number)
Number = New LinkedListNode(Of Double)(66.18)
numbers.AddFirst(Number)
For Each Dbl As Double In Numbers
LbxLinkedList.Items.Add(Dbl)
Next
End Sub
End Class
A linked list supports the concept of inserting a node but not exactly like traditional collections do it. With a linked list, you must add a node before or after an existing node used as reference. Behind the scenes, before inserting a node, you must identify the position where you want to put it. That is, you must identify what node you will use as reference:
In this case, you want to insert a new node before the Other Node. Behind the scenes, the reference between the two existing nodes must be brocken. Then the new node points to the Other Node as its next and the Other Node points at the New Node as its previous:
After the new node has been added, it must point to the previous node (Some Node in our example) as its previous item. The previous node (Some Node in our example) must now point to the new node as its next item:
As you may imagine, to insert a node, you must provide two pieces of information: a reference to the node that will succeed the new node, and the new node (or its value). If the referenced node is the first item of the list, the new node would become the new first object. To assist you with this operation, the LinkedList class provides a method named AddBefore. This method is overloaded with two versions whose syntaxes are: Public Sub AddBefore(node As LinkedListNode(Of T), _ newNode As LinkedListNode(Of T) _ ) Public Function AddBefore(node As LinkedListNode(Of T), _ value As T _ ) As LinkedListNode(Of T) In both cases, you pass a first argument as an existing node. In the first case, you must pass the LinkedListNode object that will be inserted the node. Here is an example: Public Class Exercise
Private Sub BtnLinkedList_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles BtnLinkedList.Click
Dim Values As List(Of Double) = New List(Of Double)
Values.Add(84.597)
Values.Add(6.47)
Values.Add(2747.06)
Values.Add(282.924)
Dim Numbers As LinkedList(Of Double) = New LinkedList(Of Double)(Values)
Dim Number As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(148.24)
numbers.AddFirst(number)
number = New LinkedListNode(Of Double)(35.75)
numbers.AddFirst(number)
numbers.AddLast(2747.06)
Dim Number222206 As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(2222.06)
numbers.AddLast(number222206)
number = New LinkedListNode(Of Double)(4.19)
numbers.AddFirst(number)
number = New LinkedListNode(Of Double)(66.18)
numbers.AddBefore(number222206, number)
number = New LinkedListNode(Of Double)(275.775)
numbers.AddLast(number)
For Each Dbl As Double In Numbers
LbxLinkedList.Items.Add(Dbl)
Next
End Sub
End Class
In the second version, you directly pass the value to be positioned before node.
Instead of inserting a node before an existing one, you can add it after one. The approach is logically the same as inserting a node before another, except that the sequence is reversed. First identify the node that will be used as reference. Start the process to add the new node after that one. Behind the scenes, the referenced node will point to the new node as its next and the new node will point to the existing node as its previous:
After the new node as been added, it will point to the node after it as its next. The other node will point to the new node as its previous:
If the new node is added after the last node, the new node will become the new last node. To let you insert a node after an existing node, the LinkedList class is equipped with a method named AddAfter. It comes in two versions and their syntaxes are: Public Sub AddAfter ( _ node As LinkedListNode(Of T), _ newNode As LinkedListNode(Of T) _ ) Public Function AddAfter ( _ node As LinkedListNode(Of T), _ value As T _ ) As LinkedListNode(Of T) The arguments follow the same description as the AddBefore() method, only in reverse. Here is an example: Public Class Exercise
Private Sub BtnLinkedList_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles BtnLinkedList.Click
Dim Values As List(Of Double) = New List(Of Double)
values.Add(84.597)
values.Add(6.47)
values.Add(2747.06)
values.Add(282.924)
Dim Numbers As LinkedList(Of Double) = New LinkedList(Of Double)(Values)
Dim Number As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(148.24)
Numbers.AddFirst(Number)
Dim Number3575 As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(35.75)
numbers.AddFirst(number3575)
numbers.AddLast(2747.06)
Dim Number222206 As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(2222.06)
numbers.AddLast(number222206)
number = New LinkedListNode(Of Double)(4.19)
numbers.AddFirst(number)
number = New LinkedListNode(Of Double)(66.18)
numbers.AddBefore(number222206, number)
number = New LinkedListNode(Of Double)(275.775)
numbers.AddAfter(number3575, number)
For Each Dbl As Double In Numbers
LbxLinkedList.Items.Add(Dbl)
Next
End Sub
End Class
When it comes time to delete a node, you have many options, such as deleting the first or the last node of the list. To let you delete the first node, the LinkedList class provides the RemoveFirst() method. Its syntax is: Public Sub RemoveFirst As you can see, this method takes no argument. When it is called:
To delete the last node, you can call the RemoveLast() method whose syntax is: Public Sub RemoveLast This method follows the same logic as the RemoveFirst() method, only in reverse. Here are examples of calling these methods: Public Class Exercise
Private Sub BtnLinkedList_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles BtnLinkedList.Click
Dim Values As List(Of Double) = New List(Of Double)
Values.Add(84.597)
Values.Add(6.47)
Values.Add(2747.06)
Values.Add(282.924)
Dim Numbers As LinkedList(Of Double) = New LinkedList(Of Double)(Values)
Dim Number As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(148.24)
numbers.AddFirst(number)
Dim Number3575 As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(35.75)
numbers.AddFirst(Number3575)
numbers.AddLast(2747.06)
Dim Number222206 As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(2222.06)
numbers.AddLast(Number222206)
number = New LinkedListNode(Of Double)(4.19)
numbers.AddFirst(number)
number = New LinkedListNode(Of Double)(66.18)
numbers.AddBefore(Number222206, number)
number = New LinkedListNode(Of Double)(275.775)
numbers.AddAfter(Number3575, number)
For Each Dbl As Double In Numbers
lbxLinkedListOriginal.Items.Add(Dbl)
Next
numbers.RemoveFirst()
numbers.RemoveLast()
For Each Dbl As Double In Numbers
lbxLinkedListOther.Items.Add(Dbl)
Next
End Sub
End Class
There are two ways you can delete an item inside the collection. This can be done using the Remove() method. It comes in two versions. If you know the exact value of the item you want to remove, you can call the follwing version of that method: Public Function Remove(value As T) As Boolean When calling this method, pass the value to delete. The compiler would first look for a node that has that value:
An alternative is to delete a node based on its reference. To do this, use the following version: Public Sub Remove(node As LinkedListNode(Of T)) When calling this method, pass a reference to the node you want to delete. Here is an example: Public Class Exercise
Private Sub BtnLinkedList_Click(ByVal sender As System.Object,
ByVal e As System.EventArgs) Handles BtnLinkedList.Click
Dim Values As List(Of Double) = New List(Of Double)
Values.Add(84.597)
Values.Add(6.47)
Values.Add(2747.06)
Values.Add(282.924)
Dim Numbers As LinkedList(Of Double) = New LinkedList(Of Double)(Values)
Dim Number As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(148.24)
Numbers.AddFirst(Number)
Dim Number3575 As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(35.75)
Numbers.AddFirst(number3575)
Numbers.AddLast(2747.06)
Dim Number222206 As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(2222.06)
Numbers.AddLast(number222206)
Number = New LinkedListNode(Of Double)(4.19)
Numbers.AddFirst(Number)
Number = New LinkedListNode(Of Double)(66.18)
Numbers.AddBefore(number222206, Number)
Dim Number275775 As LinkedListNode(Of Double) = New LinkedListNode(Of Double)(275.775)
Numbers.AddAfter(number3575, number275775)
For Each Dbl As Double In Numbers
lbxLinkedListOriginal.Items.Add(Dbl)
Next
Numbers.Remove(number275775)
For Each Dbl As Double In Numbers
lbxLinkedListOther.Items.Add(Dbl)
Next
End Sub
End Class
Clearing a list consists of deleting all of its item. To do this, you could continuous call one of the versions of the Remove() method. A faster solution is to call the Clear() method. Its syntax is: Public Sub Clear 


