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CS1102 Tutorial 2 ADTs
Max Tan
tanhuiyi@comp.nus.edu.sg
COM1-01-09 Tel:65164364
1
15 minute recap : ADT
What is an ADT?
Represented by an interface that
shields an implementation
Users are concerned with the interface
only
Imagine your mobile phone as an
ADT…
2
15 minute recap : ADT
To add a friend, you simply
tap the Menu button, then
select Contacts, then select
Add contact
3
15 minute recap : ADT
How to add a contact
addContact(string s)
//Method will add a contact
//name into the ADT
//Output boolean
//representing success or
//failure
4
15 minute recap : ADT
Does your manual tell you the
implementation details of how it
works?
5
15 minute recap
1. After user enters a name, we
use the Scanner class to obtain
the string
2. I check the array to see if its
full, if array is full, I double it
3. Find the first empty spot and
insert the user name there…
Etc etc
6
15 minute recap : ADT
How to add a contact
addContact(string s)
//Input a number
//When the name is added
//we check that the array is
//not full, if its full we…
BAD!!! 7
15 minute recap : ADT
Are you really interested to know the
details?
You just want to add a contact!
And that is the purpose of an ADT – to allow
the users to use it without caring about the
implementation details!
When creating an Abstract Data Type, you
have to imagine what you need from it, and
provide public methods to use the ADT
8
tutorial format
Today
Group 1 = Question 2
Group 2 = Question 3
Group 3 = Question 4
Group 4 = Question 1
Next week, Group 1 = Q3, Group 2 = Q4,
Group 3 = Q1, Group 4 = Q2 (add 1 to your
question number every week)
9
Q1
Identify two ADTs specified in the text
above and describe briefly in which
class the respective objects will be
instantiated.
10
Q1
Each order has information regarding the date of order. An order also
consists of one or more different items ..
Actually there are 3 ADTs you can identify
OrderADT or OrderList, this is a container
for Order objects
You can add, edit, delete, view orders by
using the interface provided from the
OrderADT
11
Q1
.. items with different properties like price and quantity. The user can add,
edit and delete the individual items in each order.
Order which contains the “date” for that
order and also a list of different Items
Provide methods in the Order ADT to
add/edit/delete/view the individual items
Item with properties like price and quantity
Provide methods in the Item ADT to
edit/view the item
12
Q1
Question:
What methods would you provide so
that the user would be able to print
ALL the items in ALL the Orders ?
13
Q2 (a)
.. Java Array as the data structure to store the
contacts. ..provide public methods to add, edit,
delete a contact. A contact contains the contact
name and contact number information..
How would you implement the add
method?
14
Q2 (a)
Two ways
Always insert at the end (but you have
to ensure that there are no gaps when
deleting)
Always insert into the first available
slot
Question: What are their advantages
and disadvantages?
15
Q2 (b)
.. Java Array as the data structure to store the
contacts. ..provide public methods to add, edit,
delete a contact. A contact contains the contact
name and contact number information..
What would you do when the array is
full?
16
Q2 (b)
Simply double the size of the array and
copy the contents of the old array into
the new array
Question: why double? Why not
increase array by a fixed number?
17
Q2 (c)
.. Java Array as the data structure to store the
contacts. ..provide public methods to add, edit,
delete a contact. A contact contains the contact
name and contact number information..
How would you implement the edit
method?
18
Q2 (c)
edit(string oldContactName, string
newContactName, int newContactNo)
Search through all the contacts to find
the contact we are interested in, then
update it accordingly
19
Q2 (d)
.. Java Array as the data structure to store the
contacts. ..provide public methods to add, edit,
delete a contact. A contact contains the contact
name and contact number information..
How would you implement the delete
method?
20
Q2 (d)
Two methods depending on your add
implementation
If your Add method inserts at the end,
then your delete method have to close
gaps by shifting all next elements.
delete(e) next add
q w e r t
q w r t
21
Q2 (d)
Two methods depending on your add
implementation
If your Add method inserts in the first
empty spot, then just set the slot to
empty
delete(e) next add
q w e r t u g
q w r t u g
22
Q2 (e)
.. Java Array as the data structure to store the
contacts. ..provide public methods to add, edit,
delete a contact. A contact contains the contact
name and contact number information..
Identify a potential problem resulting
from your implementation in (a) and
how it would affect your
implementation in (c) and (d).
23
Q2 (e)
What happens if you try to insert multiple
contacts with the same name?
How would you know which is the correct
contact to edit/delete later on?
Solution would be to disallow multiple
contacts with the same name
(This is quite open ended so if your answer
is something that makes sense, then it is
correct)
24
Q3
..ArrayList < ArrayList <Integer> >.. Write the
method int sumList(ArrayList<ArrayList <Integer>>
aList) that computes the sum of all the integers in
the list aList.
25
Q3
If you are confused, try to think of the
ArrayList as a box. So we have an
ArrayList of ArrayLists…
The ArrayList stores many
ArrayList<Integer> object
26
Q3
The ArrayList<Integer> is the small
box
6
2
7
51
27
Q3
So the algorithm is, take out the small
boxes one by one.
For each small box, take out the
integer objects one by one
4
28
Q3
There is no limitations to how many
level of boxes there can be
29
Q3
int sumList(ArrayList< ArrayList<Integer> > aList) throws ListOutOfBoundsException
{
int sum = 0;
//Iterates through all the available ArrayLists.
for(int i = 0; i < aList.size(); i++)
{
//Gets the individual ArrayList
ArrayList<Integer> currList = aList.get(i);
//Iterate through all the available integers
Iterate through all the
For(int j = 0; j < currList.size(); j++) small boxes
{
Integer currValue = currList.get(j);
//Java also does auto-unboxing of the primitive
//int value from the Integer object, so
// sum += currValue; would be correct.
sum += currValue.intValue();
}
}
return sum;
}
30
Q3
int sumList(ArrayList< ArrayList<Integer> > aList) throws ListOutOfBoundsException
{
int sum = 0;
//Iterates through all the available ArrayLists.
for(int i = 0; i < aList.size(); i++)
{
//Gets the individual ArrayList
ArrayList<Integer> currList = aList.get(i);
//Iterate through all the available integers
Take out a small box
For(int j = 0; j < currList.size(); j++)
{
Integer currValue = currList.get(j);
//Java also does auto-unboxing of the primitive
//int value from the Integer object, so
// sum += currValue; would be correct.
sum += currValue.intValue();
}
}
return sum;
}
31
Q3
int sumList(ArrayList< ArrayList<Integer> > aList) throws ListOutOfBoundsException
{
int sum = 0;
//Iterates through all the available ArrayLists.
for(int i = 0; i < aList.size(); i++)
{
//Gets the individual ArrayList
ArrayList<Integer> currList = aList.get(i);
//Iterate through all the available integers
for(int j = 0; j < currList.size(); j++)
{ Iterate through all the
Integer currValue = currList.get(j);
//Java also does auto-unboxing of the primitive integers in that selected
//int value from the Integer object, so small box
// sum += currValue; would be correct.
sum += currValue.intValue();
}
}
return sum;
}
32
Q3
int sumList(ArrayList< ArrayList<Integer> > aList) throws ListOutOfBoundsException
{
int sum = 0;
//Iterates through all the available ArrayLists.
for(int i = 0; i < aList.size(); i++)
{
//Gets the individual ArrayList
ArrayList<Integer> currList = aList.get(i);
//Iterate through all the available integers
for(int j = 0; j < currList.size(); j++)
{ Get each integer and sum
Integer currValue = currList.get(j);
//Java also does auto-unboxing of the primitive it up
//int value from the Integer object, so
// sum += currValue; would be correct.
sum += currValue.intValue();
}
}
return sum;
}
33
Q3
int sumList(ArrayList< ArrayList<Integer> > aList) throws ListOutOfBoundsException
{
int sum = 0;
//Iterates through all the available ArrayLists.
for(int i = 0; i < aList.size(); i++)
{
//Gets the individual ArrayList
ArrayList<Integer> currList = aList.get(i);
//Iterate through all the available integers
for(int j = 0; j < currList.size(); j++)
{ Get each integer and sum
Integer currValue = currList.get(j);
//Java also does auto-unboxing of the primitive it up
//int value from the Integer object, so
// sum += currValue; would be correct.
sum += currValue.intValue();
}
}
return sum;
}
Note that Java can handle auto-unboxing
of the primitive wrappers.
To avoid confusion to yourself, you
should always try to use the methods 34
provided for the Java classes
Q4
About planning before writing code!
Think of use cases – the interaction
that you need to perform on the game
In this question, you need to write the
ADTs for Minesweeper as well as the
Tiles in the grid
35
Q4
Game Randomly Check for Win
starts generate 20 win/lose
mines on condition
the tiles
Lose
Read User
Input
leftClickEvent rightClickEve
(x, y) nt(x, y)
36
Q4
What can be performed on the game?
We consider only left click and right
click actions on the grid
You should localize the methods into
the correct ADTs.
37
Q4
Three classes
In UserInterface, Minesweeper and
Tile
You only need to write for
Minesweeper and Tile. UserInterface
should be interchangable, so all
methods should be in Minesweeper
38
Q4
Lets imagine how the game might
start
Initialize the game board of 15 x 15
tiles, and with a probability of 0.1 that
a tile is a mine.
(Of course the real game sets a fixed
number of mines, but we try to keep
things simple)
39
Q4
Constructor of the MineSweeper class to
handle the size of grid
Grid size does not change so use a 2
dimensional array.
Since each tile contains some information,
we use a Tile ADT to represent this
information.
The constructor of the Tile class will take in
the probability value to determine if a tile is a
mine (another constructor could take in a
isMine true/false flag).
40
Q4
Before waiting for mouse click
1. Check victory
2. Check lost
3. Get the representation for each tile
– could be flagged, or uncovered mine
or etc
4. Get the mine counter and display
the grid
41
Q4
class Minesweeper{
boolean hasWon()
boolean hasLost()
String getTileString(int x, int y)
int getMineCounter()
}
42
Q4
Left click
Uncovers a tile if it is not uncovered.
If its neighbors has mines, count the
number of mines in its neighbors and
display it.
How many functions is required?
43
Q4
Minesweeper{
boolean hasWon()
boolean hasLost()
String getTileString(int x, int y)
int getMineCounter()
boolean isUncovered(int x, int y)
void uncover(int x, int y)
int getNeighborMines(int x, int y)
}
44
Q4
Right click
Toggles the flag status on a tile if it is
not uncovered yet
45
Q4
Minesweeper{
boolean hasWon()
boolean hasLost()
String getTileString(int x, int y)
int getMineCounter()
boolean isUncovered(int x, int y)
void uncover(int x, int y)
int getNeighborMines(int x, int y)
int toggleFlag(int x, int y)
}
46
Q4
How did you store the tiles?
A two dimensional array is easy!
What functions are needed in the Tile
class? Look back at the Minesweeper
class to determine the algorithm for
each method!
47
Q4
For example :
boolean isUncovered(int x, int y)
Algorithm : Go to the grid[x][y] to
access the tile, and ask the tile if it is
uncovered.
Hence Tile needs a isUncovered()
method!
48
Q4
class Tile{
int toggleFlag()
void uncover()
public boolean isUncovered()
public string getTileString()
bool isMine()
}
49
Q4
Why is getNeighborMines() in the
Minesweeper class instead of the Tile
class ?
The tiles do not store its neighbor’s
indices! But the Minesweeper class
knows! (Because an array is used to
store all the tiles)
50
Q4
In this question, the Tile class is abstract to
everyone who needs to use the
Minesweeper class.
Only need to know about the Minesweeper
class
Can your interface be changed? Interface
should only accept inputs and give outputs
and perform nothing else – your
Minesweeper ADT should reflect that.
51
Q4
There are countless ways to solve this
problem
Once you have the skeleton methods,
it will be a simple process to just fill in
the code in the methods!
ADT exercise: Try implementing your
MineSweeper ADT and then writing a
command line interface for it.
52
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