CS2 OO Design: a restaurant example Trees, tree design, tree traversal presentation

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CS2 OO Design: a restaurant example Trees, tree design, tree traversal

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... a table in smoking. Waiting for a table in non-smoking. Waiting for a ... Non-smoking. Designing a Solution. We might want to consider sketching some screens: ... –

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Title: CS2 OO Design: a restaurant example Trees, tree design, tree traversal

1
CS2OO Design a restaurant exampleTrees, tree
design, tree traversal
2
Basic Design

Software design is an art not a science
It is best learned by experience hopefully with
some expert guidance
This lecture will not make you an expert
The goal is to give you a simple basic structure
to get you started in the process.
No matter what your major you will take a number
of design courses before you leave Tech.

3
Simple Steps

1. Understand the problem
Problem statement
Discussion with clients
2. Develop cases or scenarios
Functions that your program must perform
Might be menu items
Might be events which trigger action
3. Plain English
Describe situation
Describe scenarios

4
Simple Steps

4. Apply Object Oriented thinking
Analyze the plain English
Nouns - Objects
Verbs - Methods
Imagine the structure
"has a" relationships (fields)
"is a" hierarchical structures
Consider communication
Who has to communicate with whom?
Who has to know about what?

5
Simple Steps

5. Put the design on paper (or the wall)
Indicate classes
Their methods
Their fields
Who they need to talk to
Indicate hierarchies
6. Run the cases or scenarios against the design
Modify, modify, modify
7. Code a class at a time
USE A TEST/DEBUG main IN EACH
Start at the bottom
Compile test frequently

6
An Example

A friend owns a restaurant. He knows that youre
a Java wizard and he asks for your help with a
little problem.
His business is very good and he is so busy that
his maitre d has trouble keeping track of people
waiting for tables.
He would like a program that would manage the
various lists of people waiting. These include
Waiting for a table in smoking
Waiting for a table in non-smoking
Waiting for a very big table
etc.
Since different maitre ds may use different
techniques he would like something very simple
and very flexible.

7
An Example

After some discussion with your friend you reach
the following statement of program function
The program will display a menu with the
following choices
Create a new list
Add a customer to a list
Seat a customer from a list
Quit
This seems like a good starting point although
you keep in the back of your mind the fact that
most people will realize they want any given
program to do more once they see it in operation.

8
Designing a Solution

So now you have accomplished the first step
1. Understand the problem
Problem statement
Discussion with clients
Now lets look at the next step
2. Develop cases or scenarios
Functions that your program must perform
Might be menu items
Might be events which trigger action

9
Designing a Solution

Lets go back and look at the menu
The program will display a menu for the maitre d
with the following choices
Add a new list
Add a customer to a list
Seat a customer from a list

10
Designing a Solution

This seems like a pretty good description of the
scenarios we need to be able to perform. So this
will serve as a start for step 3 also
3. Plain English
Describe situation
Describe scenarios

11
Designing a Solution

We might consider adding some additional detail
and an extra scenario
The program will be run by the maitre d of a
restaurant
The program will startup
The program will display a menu with the
following choices
Create a new list
Add a customer to a list
Seat a customer from a list
Quit

12
Designing a Solution

We might want to consider sketching some screens

MAITRE D Enter 1. To create a new list 2. To
add a customer to a list 3. To seat a customer
from a list 4. To quit Choice 1
13
Designing a Solution

We might want to consider sketching some screens

MAITRE D Create a New List Enter the name for
the new list Non-smoking
14
Designing a Solution

We might want to consider sketching some screens

MAITRE D Create a New List Enter the name for
the new list Smoking
15
Designing a Solution

We might want to consider sketching some screens

MAITRE D Create a New List Enter the name for
the new list Big group
16
Designing a Solution

We might want to consider sketching some screens

MAITRE D Add a Customer to a List Enter 1.
For Non-smoking 2. For Smoking 3. For Big
group Choice 2 Enter Customer Smith
17
Designing a Solution

We might want to consider sketching some screens

MAITRE D Seat a Customer from a List Enter 1.
For Non-smoking 2. For Smoking 3. For Big
group Choice 1 You may now seat the Jones
party. Press Enter when done. ltENTERgt
18
OO Thinking

Lets do the first part of step 4
4. Apply Object Oriented thinking
Analyze the plain English
Nouns - Objects
Verbs - Methods
Imagine the structure
"has a" relationships (fields)
"is a" hierarchical structures
Consider communication
Who has to communicate with whom?
Who has to know about what?

19
Designing a Solution

Now lets go back and look at our program
information
The program will be run by the maitre d of a
restaurant
The program will startup
The program will display a menu with the
following choices
Create a new list
Add a customer to a list
Seat a customer from a list
Quit
Lets mark nouns in blue.

20
Designing a Solution

Now lets go back and look at our program
information
The program will be run by the maitre d of a
restaurant
The program will startup
The program will display a menu with the
following choices
Create a new list
Add a customer to a list
Seat a customer from a list
Quit
Lets mark nouns in blue.
Lets mark verbs in red

21
Designing a Solution

Now lets go back and look at our program
information
The program will be run by the maitre d of a
restaurant
The program will startup
The program will display a menu with the
following choices
Create a new list
Add a customer to a list
Seat a customer from a list
Quit
Lets mark nouns in blue.
Lets mark verbs in red

22
OO Thinking

Now for the remainder well need an additional
tool
4. Apply Object Oriented thinking
...
Imagine the structure
"has a" relationships (fields)
"is a" hierarchical structures
Consider communication
Who has to communicate with whom?
Who has to know about what?

23
Design Technique

The basic building block on Object Oriented
Programming is the class so lets use some kind
of symbol for a class. This scheme could be used
on a big piece of paper, 3 x 5 cards or even a
whiteboard.

24
Design Technique

So our nouns were program, maitre d, restaurant,
menu, customer, choices, list.
Well select some likely candidates for classes
Note There is no right/wrong for this step i.e.
use pencil!

Certainly were going to have some kind of list.
25
Design Technique

So our nouns were program, maitre d, restaurant,
menu, customer, choices, list.
Well select some likely candidates for classes
Note There is no right/wrong for this step i.e.
use pencil!

In fact, if we think about it we might want it to
be like a Queue???
26
Design Technique

So our nouns were program, maitre d, restaurant,
menu, customer, choices, list.
Well select some likely candidates for classes
Note There is no right/wrong for this step i.e.
use pencil!

Deep in our heart we know that a Queue is
somehow going to require nodes
27
Design Technique

So our nouns were program, maitre d, restaurant,
menu, customer, choices, list.
Well select some likely candidates for classes
Note There is no right/wrong for this step i.e.
use pencil!

Well put the Node under the list and come back
to it later
28
Design Technique

So our nouns were program, maitre d, restaurant,
menu, customer, choices, list.
Well select some likely candidates for classes
Note There is no right/wrong for this step i.e.
use pencil!

Were also pretty sure that we need some customers
29
Design Technique

So our nouns were program, maitre d, restaurant,
menu, customer, choices, list.
Well select some likely candidates for classes
Note There is no right/wrong for this step i.e.
use pencil!

And perhaps a menu?
30
Design Technique

So our nouns were program, maitre d, restaurant,
menu, customer, choices, list.
Well select some likely candidates for classes
Note There is no right/wrong for this step i.e.
use pencil!

Maybe well include the Maitre d (Imagine him
holding a clipboard?)
31
Design Technique

So our nouns were program, maitre d, restaurant,
menu, customer, choices, list.
Remember, we can always go back and add things.
At this point we are trying to see the big
picture...

32
Design Technique

Now lets think about some of the things that
these objects would contain...

33
Design Technique

Now lets think about some of the things that
these objects would contain...

34
Design Technique

Now lets think about some of the things that
these objects would contain...

35
Design Technique

Now lets think about some of the things that
these objects would contain...

36
Design Technique

Now look at the fields and also remember the
verbs run, startup, display, create, add, seat,
quit.

37
Design Technique

Now stop and think about structure
Well have lists of Nodes, the Nodes will contain
Customers, the MaitreD will have perhaps an array
of lists. Make sense?
The Menu class...will instances be different
menus? Does it need to be a class? Could it just
be methods in MaitreD?

38
Design Technique

Lets consider some scenarios...
Startup We might have a small Driver class or
perhaps just let MaitrD contain the startup main
java MaitreD

(main)
39
Design Technique

Lets consider some scenarios...
Startup We would simply have to have a looping
method that displayed a menu and used a switch to
do the right thing.

(main)
40
Design Technique

Lets consider some scenarios...
Create Get the name (maybe the list needs a
name), make a list object, put it into the array
of lists. No problem?

(main)
41
Design Technique

Lets consider some scenarios...
Add Loop through the list array and show the
list names . Get a choice, then get a customer
name, create a customer object enqueue it.
Hmmm, maybe this separate Menu class is not
helping?

(main)
42
Design Technique

Lets consider some scenarios...
Note The objective here is not to be pretty!

Class Menu
(main)
Fields choice
Comm
Methods printMenu getChoice
43
Design Technique

Okay, maybe neat?

Class MaitreD
(main)
Fields array? of lists
Methods create add seat quit printMenu getChoice

Comm
44
Design Technique

Okay, maybe neat?

Class MaitreD
(main)
Fields array? of lists
Methods create add seat quit printMenu getChoice

Comm
45
Design Technique

The other scenario is when we wish to seat a
customer. We assume that a table is now available
that corresponds to a given list and we simply
dequeue the head of that list and print out that
name.

Class MaitreD
(main)
Fields array? of lists
Methods create add seat quit printMenu getChoice

Comm
46
Design Technique

What about these "Comm" areas?
In this case its pretty straightforward. The
object/class that creates another object will be
the one communicating with it so this is simple.
We would use these for example if a customer
needed to know about which list he was in.

47
Time for Coding?

Stack up the cards or otherwise try to establish
a bottom up priority for coding.

48
Time for Coding?

class Customer
private String strName
public Customer(String strName)
setName(strName)
public void setName(String s)
strName s
public String getName()
return strName

49
Time for Coding?

// class Customer (continued)
public static toString()
return getName()
public static void main(String args)
Customer c1, c2
c1 new Customer("Smith")
c2 new Customer("Jones")
System.out.println(c1 "," c2)
c1.setName("Fred")
System.out.println(c1.getName())
// customer

50
Time to Code

Our Node could be specific to this problem.
Or we could use the linked list Node (and perhaps
even the DataNode) we already discussed.
Why do we need a special node for a customer?
So far we dont.
But experience says that perhaps well be adding
additional information about each customer?

51
Time to Code

Our List which we recognize as a Queue type data
structure could be implemented in several
different ways
We could use an existing Java class such as
Vector which well discuss in the near future.
We could write one of our own.
Typical solution in a beginning programming class

class List
private Node head
private Node tail
private String name
public List(String name)
setName(name)
setHead(null)
setTail(null)
public void setHead(Node head)
this.head head
public Node getHead()
return head

// class List (continued)
public void setTail(Node tail)
this.tail tail
public Node getTail()
return tail
public String getName()
return name
public void setName(String name)
this.name name

// class List (continued)
public boolean isEmpty()
return (getHead null)
public void add(Object obj)
if (isEmpty())
setHead(new Node(obj))
setTail(getHead())
else // add to end
getTail().setNext(new Node(o))
setTail(getTail().getNext())
// add

// class List (continued)
public Object remove()
Object retVal
if (isEmpty())
retVal null
else
retVal getHead().getData()
if(getHead() getTail())
setHead(null)
setTail(null)
else
setHead(getHead().getNext())
return retVal
// remove

// class List (continued)
public String toString()
if (isEmpty())
return "Empty"
else // call the Node classs toString()
return getHead().toString()
public static void main(String args)
List ell new List("TestList")
ell.add("Item 1")
ell.add("Item 2")
System.out.println(ell)
System.out.println(ell.remove())
System.out.println(ell.remove())
if(ell.remove() null)
System.out.println("null test passed")
// main
// List

57
Time to Code

Now the method that will get sent to java at
startup.
Lets review what it needs to do
Hold a reference to an array of lists
Constructor
Make the array to hold lists
MenuLoop
do
Print menu
Get Choice
Switch
while (not quit)
Main
Instantiate
Call MenuLoop

public class MaitreD
private List lists
int listCount
public MaitreD()
list new ListMAXARRAY
listCount 0
// constructor

// class MaitreD (continued)
public void menuLoop()
do
choice printMenu1()
switch(choice)
case CREATE
create()
break
case ADD
add()
break
case SEAT
seat()
break
case QUIT
break
default
break

// MaitreD (continued)
private int printMenu1()
System.out.print(MENU1)
return Integer.parseInt(IOHelper.readLine())
// printMenu1
private void create()
System.out.print(MENU2)
listCount
if(listCount lt MAXARRAY)
listslistCount - 1
new List(IOHelper.readLine())
else // cannot add the list
System.out.println(
"Maximum number of lists exceeded -- "

// MaitreD (continued)
private void add()
int choice
System.out.println(MENU3)
for (int i0 i lt listCount i)
System.out.print(" " (i1) MENU4)
System.out.println(listsi.getListName())
System.out.print(MENU5)
choice Integer.parseInt(IOHelper.readLine())
// Should put error handler here to insure
valid
// list number
System.out.print(MENU6)
listschoice.add(newCustomer(IOHelper.readLine
()))
// add

// MaitreD (continued)
private void seat()
int choice
System.out.println(MENU7)
for(int i0 i lt listCount i)
System.out.println(" " (i1) MENU4
listsi.getListName())
System.out.print(MENU5)
choice Integer.parseInt(IOHelper.readLine())
// Would put error handler here to insure valid
// list number
System.out.println(
MENU8 listschoice.remove() MENU9")
IOHelper.readLine() // Wait for "Enter"

// MaitreD (continued)
public static void main(String args)
// a little testing main
MaitreD m new MaitreD()
m.menuLoop()

interface MaitreDConstants
public static final int MAXARRAY 20
public final static String MENU1
"MAITRE D\n\nEnter\n
"1. To create a new list\n
"2. To add a customer to a list\n
"3. To seat a customer from a list\n
"4. To quit\n\n
"Choice "
public final static String MENU2
"MAITRE D Create a New List\n\n
"Enter the name for the new list "

// MaitreDConstants (continued)
public final static String MENU3
"MAITRE D Add a Customer to a List\n\n"
"Enter "
public final static String MENU4 " For "
public final static String MENU5 "Choice "
public final static String MENU6
"Enter Customer "
public final static String MENU7
"MAITRE D Seat a Customer from a List\n
"Enter\n"
public final static String MENU8
"You may now seat the "

66
Summary

Design before coding.
Think OO
Nouns,
verbs,
communication.
Code incrementally
Test incrementally!
Use test mains

67
Questions?
68
Trees

Hierarchical data structure
Nodes with 0 to many children
One special node designated root
Acyclic
Recursive definition

69
Binary Trees

Hierarchical data structure
Nodes with 0 to 2 children
One special node designated root
Acyclic
Recursive definition
Used for BST

70
Binary Search Trees

Binary Tree
Left subtree contains key values less than node
Right subtree contains key value greater than
node
No duplicates

50
40
95
42
30
Normally handles specially
63
99
37
10
71
Binary Search Trees

Performance
Search O(log N)
Insert O(log N)
Traverse O(N)
Performance O()'s assume tree is relatively
balanced

50
50
40
40
95
30
42
30
63
99
10
37
10
72
Data Structure Design
73
Recall Linked ListsSome Design Alternatives
class Object
default behavior
class DataNode
Object data DataNode getData setData equals toStri
ng
class DataNode
74
Recall Linked ListsSome Design Alternatives
class Object
Object data DataNode getData setData equals toStri
ng compareTo
interface Comparable
class DataNode
implements
class DataNode implements Comparable
75
Recall Linked ListsSome Design Alternatives
class Object
interface Comparable
Object data DataNode getData setData equals toStri
ng compareTo
interface DataNodeType
class DataNode
getData setData
interface DataNodeType extends Comparable
class DataNode implements DataNodeType
76
Recall Linked ListsSome Design Alternatives
One Way
class Object
interface Comparable
interface DataNodeType
class DataNode
getData setData
ListNode next ListNode getNext setNext equals toSt
ring compareTo
interface ListNodeType
class ListNode
getNext setNext
interface ListNodeType extends DataNodeType
class ListNode extends DataNode implements
ListNodeType
77
Recall Linked ListsSome Design Alternatives
Another...
class Object
interface Comparable
class DataNode
ListNode next ListNode getNext setNext equals toSt
ring compareTo
interface ListNodeType
class ListNode
getData setData getNext setNext
class ListNode extends DataNode implements
ListNodeType,Comparable
78
Wait, (Bill Monica) have you lost your mind?

Well, frankly, yes but let's not talk about that
now.

79
What's the point?

You will design data structure objects like
ListNodes and TreeNodes (in a second).
You will also design container classes like
LinkedList and BinaryTree
You can make your LinkedList hold a ListNode or a
ListNodeType
You can make your BinaryTree hold a TreeNode or a
TreeNodeType
In both cases the latter choice will give you a
more flexible design.
We'll explain why after we talk a little about
trees

80
Wow!
class Object
interface Comparable
interface DataNodeType
class DataNode
interface ListNodeType
class ListNode
interface TreeNodeType
class TreeNode
81
Or
class Object
interface Comparable
class DataNode
class ListNode
interface ListNodeType
interface TreeNodeType
class TreeNode
82
Or even...
class Object
interface Comparable
class ListNode
interface ListNodeType
interface TreeNodeType
class TreeNode
83
Let's use this one
class Object
interface Comparable
class DataNode
class ListNode
interface ListNodeType
interface TreeNodeType
class TreeNode
84
The Interfaces

public interface ListNodeType extends Comparable
public void setData(Comparable data)
public Comparable getData()
public void setNext(ListNodeType next)
public ListNodeType getNext()
public interface TreeNodeType extends Comparable
public void setData(Comparable data)
public Comparable getData()
public void setLeft(TreeNodeType left)
public TreeNodeType getLeft()
public void setRight(TreeNodeType right)
public TreeNodeType getRight()

85
The Classes

public class DataNode implements Comparable
private Comparable data
public DataNode(Comparable data)
/Constructor/
public void setData(Comparable data)
/implementation details not shown/
public Comparable getData() /implementation/
public boolean equals(Object o)
/implementation/
public String toString() /implementation/
public int compareTo(Object o)
/implementation/
public static void main(String args)
/implementation/

86
The Classes

public class ListNode extends DataNode implements
ListNodeType
public ListNode(Comparable data)
/Constructor/
public void setNext(ListNodeType next)
/implementation/
public ListNodeType getNext() /implementation/
public boolean equals(Object o)
/implementation/
public boolean toString()
public static void main(String args)
/implementation/

87
The Classes

public class TreeNode extends DataNode implements
TreeNodeType
public TreeNode(Comparable data)/Constructor/
public TreeNode(Comparable data,
TreeNodeType left, TreeNodeType right)
/Constructor/
public void setLeft(TreeNodeType left)
/implementation/
public TreeNodeType getLeft() /implementation/
public void setRight(TreeNodeType right)
/implementation/
public TreeNodeType getRight()
/implementation/
public boolean equals(Object o)
/implementation/
public static void main(String args)
/implementation/
public String toString()

88
Java
cs1322
Learning about the Glorious Chairmans Nodes will
promote unity.
89
The Tree Class

In a similar fashion to Linked Lists...
Now that we have a tree node which has
A Comparable data reference (since it's going to
be a BST)
A left and a right reference to another tree node
Appropriate nodish methods (equals, compareTo,
toString()
And, of course, a debug main
We can design a Tree class

90
What will it need?

A reference to a root node
A constructor
Traverse methods
in order
preorder
postorder
breadth first?
insert
contains
nodeCount
height
delete
main

Let's code!
91

class Tree
private TreeNodeType root
public Tree()
root null
/ toString ??? /
public void inorder()
inorder(root)

// class Tree (continued)
private void inorder(TreeNodeType current)
if(current ltgt null)
inorder(current.getLeft())
System.out.println(current)
inorder(current.getRight())

93
Outline of In-Order Traversal
Recall

Three principle steps
Traverse Left
Process current (root) node (Current node)
Traverse Right
The process can be anything
print the node value
insert the node in some other structure
look for some value
do some math with each node
etc.
Separate process from mechanics of traversal

Traverse the tree "In order"
Visit currents left sub-tree
Visit current node process data
Visit currents right sub-tree

// class Tree (continued)
public static void main(String args)
TreeNode t2 new TreeNode("T2")
TreeNode t4 new TreeNode("T4")
TreeNode t9 new TreeNode("T9")
TreeNode t3 new TreeNode("T3", t2, t4)
TreeNode t8 new TreeNode("T8", null, t9)
TreeNode t5 new TreeNode("T5", t3, t8)
/ This is strange /
Tree test new Tree()
test.root t5 / !!!!!!! Done only to test
!!! /
test.inorder()
// End of class (for testing)

5
8
3
2
9
4
96
The other classic traversals
97

// class Tree (continued)
public void preorder()
preorder(root)
private void preorder(TreeNodeType current)
if(current ltgt null)
System.out.println(current)
preorder(current.getLeft())
preorder(current.getRight())

// class Tree (continued)
public void postorder()
postorder(root)
private void postorder(TreeNodeType current)
if(current ltgt null)
postorder(current.getLeft())
postorder(current.getRight())
System.out.println(current)

99
Other ideas...
100

// class Tree (continued)
public int countNodes()
return countNodes(root)
private int countNodes(TreeNodeType current)
if(current null)
return 0
else
return 1 countNodes(current.getLeft())
countNodes(current.getRight())

101

// class Tree (continued)
public String toString()
return toString(root)
private String toString(TreeNodeType current)
if(current null)
return ""
else
return toString(current.getLeft())
(current.getData() null
? "(null data)" current.getData() )
toString(current.getRight())

102
(No Transcript)
103
But why TreeNodeType???

Advanced Java Topic

104
Advanced Java Topic

Why are we covering advanced topics in an
introductory course?
Okay, it's not that advanced
You might be coding Java for money in the near
future and this is a good thing to understand

105
But why???

Here is what makes sense
A node should hold Comparables instead of just
Objects
When sorting is important
When order is important
My LinkedList and my Tree
have head references which are ListNodeType and
TreeNodeType(remember, those are interfaces!)
don't actually have to be ListNodes and
TreeNodes,
they just have to implement certain methods.
Here is what makes no sense
Why would I ever want to put anything but a
TreeNode in my Tree?
Why would I ever want to put anything but a
ListNode in my list?

106
Performance

Suppose you are writing a real application and
you have a SwissArmyKnife class. It does all
kinds of cool things (slices, dices, juliennes,
etc.)
Youre going to have about 60,000 SwissArmyKnife
objects.
They will move back and forth between a Tree and
a LinkedList.
The conventional Node-with-a-reference-to-an-objec
t approach works but there is a lot of overhead
Every time we remove a SwissArmyKnife object from
one structure and put it in the other we have to
discard a node which must be garbage collected
and allocate a new Node for the other structure
This is costly
If instead we just add to SwissArmyKnife the
appropriate data, next, left and right fields
along with appropriate accessors and modifiers we
can actually put the object directly in the list
or tree (Note This might require modification of
the LinkedList or Tree class.)

107
Performance

In other words, we could have some class of
interest (SwissArmyKnife) that happens to satisfy
perhaps both interfaces!
TreeNodeType
ListNodeType
As such, objects from that weird class could be
stored in a tree, or in a list.
This is so because the said object
is a TreeNodeType and
is a ListNodeType as well!

108
Performance

Its like having an amphibious vehicle
Satisfies roadVehicleInterface
Satisfies waterVehicleInterface
Its a car
Its a boat
It can be stored
In the garage
In the marina

109
Questions?

Okay, then back to it We almost have a BST

110
Inserting into a BST

We have a Binary Search Tree
It can be empty
Or have some elements in it already
We want to add an element to it
Inserting/adding involves 2 steps
Find the correct location
Do the steps to add a new node
Must maintain "search" structure

111
Finding the Correct Location
Start withthis tree
12
41
3
98
7
112
Finding the Correct Location
Where would 4 be added?
12
41
3
98
7
113
Finding the Correct Location
4
To the topdoesnt work
12
41
3
98
7
114
Finding the Correct Location
12
41
4
98
3
In the middledoesnt work
7
115
Finding the Correct Location
12
41
3
98
7
At the bottomDOES work!
4
116
Finding the Correct Location

Must maintain "search" structure
Everything to left is less than current
Everything to right is greater than current
Adding at the "bottom" guarantees we keep search
structure.
Well recurse to get to the "bottom" (i.e. when
current.getRight() null
or current.getLeft() null)

117
Insert

As is by now typical to you...
We will use a helper module approach
The first module check to see if the root is null
If it is the new node is added immediately
If not, call the helper.
Since it knows it will be getting a node it can
check for which direction to insert
If it finds a null reference in that direction,
add a node
If not recurse!

118
Insert

public void insert(Comparable c)
TreeNode temp new TreeNode(c)
if (root null)
root temp
else
insert(root, temp)

119

public void insert(TreeNodeType cur, TreeNodeType
temp)
if(cur.compareTo(temp) gt 0)
if(cur.getLeft() null)
cur.setLeft(temp)
else
insert(cur.getLeft(), temp)
else if(cur.compareTo(temp) lt 0)
if(cur.getRight() null)
cur.setRight(temp)
else
insert(cur.getRight(), temp)
else
throw new RuntimeException("Duplicate node
found")

120
Questions?
121
Deleting from a BST
122
The Scenario

We have a Binary Search Tree and want to remove
some element based upon a match.
Must preserve "search" property
Must not lose any elements (i.e. only remove the
one targeted element)

123
BST Deletion

Search for desired item.
If not found, then return NULL or print error.
If found, perform steps necessary to accomplish
removal from the tree.

124
Four Scenarios of Deletion

Delete a leaf node
Delete a node with only one child (left)
Delete a node with only one child (right)
Delete a node with two children
Cases 2 and 3 are comparable and only need slight
changes in the conditional statement used

125
Delete a Leaf Node

Simply make the parent node null. This will
remove the node from the tree.

126
Delete a Leaf Node

Simply make the parent node null. This will
remove the node from the tree.
Lets delete the 42.

127
Delete a Leaf Node
Simply make the parent node null. This will
remove the node from the tree.
128
Delete a Leaf Node

Simply make the parent node null. This will
remove the node from the tree.
Ta-Da

129
Questions?
130
Delete a Node with One Child

Determine if it has a left or a right child.
Move the child reference to the parent reference

131
Delete a Node with One Child

Determine if it has a left or a right child.
Move the child reference to the parent reference
Lets to the 14

132
Delete a Node with One Child

Determine if it has a left or a right child.
Move the child reference to the parent reference

133
Delete a Node with One Child

Determine if it has a left or a right child.
Ta-Da

134
Delete a Node with One Child
Determine if it has a left or a right
child. Move the child reference to the parent
reference Now, the 71
135
Delete a Node with One Child
Determine if it has a left or a right
child. Move the child reference to the parent
reference
136
Delete a Node with One Child
Determine if it has a left or a right
child. There!
137
Questions?
138
Delete a Node with Two Children

Copy a replacementvalue from a descendentnode.
- Largest from left
- Smallest from right
Then delete that descendent node to remove the
duplicate value.
- We know this will be an easier case.

139
Delete a Node with Two Children
Lets delete 50.
140
Delete a Node with Two Children
Look to the leftsub-tree.
141
Delete a Node with Two Children
Find and copy thelargest value(this will erase
theold value but createsa duplicate).
142
Delete a Node with Two Children
The resulting treeso far.
143
Delete a Node with Two Children
Now delete theduplicate fromthe left sub-tree.
144
Delete a Node with Two Children
The final resultingtree still has the proper
searchstructure.
145
Delete a Node with Two Children
Lets delete 94.
146
Delete a Node with Two Children
Look to the rightsub-tree.
147
Delete a Node with Two Children
Find and copy thesmallest value(this will erase
theold value but createsa duplicate).
148
Delete a Node with Two Children
The resulting treeso far.
149
Delete a Node with Two Children
Now delete theduplicate fromthe left sub-tree.
150
Delete a Node with Two Children
The final resultingtree still has
searchstructure.
151
Delete Overview

Deleting a node from a binary search tree
involves two steps
Search for the element
Then perform the deletion
We must preserve the search structure and only
delete the element which matches.
Four scenarios
Deleting a leaf node
Deleting a node with only the left child
Deleting a node with only the right child
Deleting a node with both children

152
On to the code!
153
First some constants...

private static final int BOOGABOOGA -1
private static final int NOCHILDREN 0
private static final int LEFTCHILD 1
private static final int RIGHTCHILD 2
private static final int TWOCHILDREN 3

154
A handy method

private int countChildren(TreeNodeType n)
int retval BOOGABOOGA
if(n ! null)
if(n.getLeft() null n.getRight()
null)
retval NOCHILDREN
if(n.getLeft() ! null n.getRight()
null)
retval LEFTCHILD
if(n.getLeft() null n.getRight() !
null)
retval RIGHTCHILD
if(n.getLeft() ! null n.getRight() !
null)
retval TWOCHILDREN
return retval

155
The public method

public void delete(Comparable target)
root delete(root, target)

156

private TreeNodeType delete
(TreeNodeType cur, Comparable
target)
TreeNodeType temp
TreeNodeType retval null
if(cur ! null)
if(cur.getData().compareTo(target) 0)
switch(countChildren(cur))
case NOCHILDREN // No children
retval null
break
case LEFTCHILD // Left child only
retval cur.getLeft()
break
case RIGHTCHILD // Right child only
retval cur.getRight()
break

157

case TWOCHILDREN // Node to delete has two
// children
retval cur
// Special case...
left child has null right child
if(cur.getLeft().getRight() null)
cur.setData(cur.getLeft().getData())
cur.setLeft(cur.getLeft().getLeft())
else
temp cur.getLeft()
while
(temp.getRight().getRight() !
null)
temp temp.getRight()
cur.setData(temp.getRight().getData())
temp.setRight(temp.getRight().getLeft())
break

158

default
System.err.println
("The impossible has
happened!!!")
System.exit(0)
// end switch removing the cur node
else if(cur.getData().compareTo(target) gt 0)
// Recursing Left
cur.setLeft(delete(cur.getLeft(), target))
retval cur
else
// recursing Right
cur.setRight(delete(cur.getRight(), target))
retval cur
return retval

159
Questions?
160

class BigDaddy
public BigDaddy()
System.out.println("Whos your Daddy?")

161

class BadDad extends BigDaddy
public BadDad()
System.out.println("This is BadDad!")
ruin() // which ruin method???
public void ruin()
// Notice this does NOT get called!
System.out.println("Maniacal Laugh!!!")

162

class Bad extends BadDad
private int x 0 // bad programming!
public Bad()
System.out.println("Whos Bad?")
public void setX(int x)
this.x x
public int getX()
return x
public void ruin()
System.out.println("About to set x to 42")
setX(42)
System.out.println("Verifying... x "
getX())
public static void main(String args)
Bad b new Bad()
System.out.println("Value of x is now "
b.getX())

163
What's the output?
Whos your Daddy? This is BadDad! About to set x
to 42 Verifying x 42 Whos Bad? Value of x is
now 0
164
Questions?
165
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