CS1102 Tut 2 ADTs

1
CS1102 Tut 2 ADTs

• Max Tan
• tanhuiyi_at_comp.nus.edu.sg
• S15-03-07 Tel[phone]

2
First 15 minutes

• Any questions regarding tutorial/lecture
  materials?
• Any feedback regarding Tutorials/Labs?
• Your graded lab is up. You only have FIVE
  submissions, be sure to do extensive testing on
  your own machine before submission!
• CS1102 Help session on Monday 5 7pm.

3
First 15 minutes

• Lecture 2 Data abstraction slide 86

Why can we define a List type to a ArrayList
object ? What happens when we call the add
method in aList?
4
First 15 minutes

• ArrayList is a subclass of List this means that
  ArrayList is a special kind of list!
• Polymorphism
• So ArrayList is a List!
• But is List an ArrayList?
• ArrayList a new List()

Incompatible type error!
5
First 15 minutes

• Lecture 2 Data abstraction slide 86

Why can we define a List type to a ArrayList
object ? What happens when we call the add
method in aList?
6
First 15 minutes

• add() is a method defined in the List class
• This means that all subclasses of List will
  either inherit the method OR override the method
  with their own implementation of add
• In compile time, the aList object is determined
  to be a ArrayList, and the add method in
  ArrayList is used (assuming it overrides
  List.add)

7
First 15 minutes
class eg1 public static void
main(Stringargs) Mammal m1 new
Mammal() m1.printCharacteristic() Mammal
m2 new Man() m2.printCharacteristic() m2.p
rintMoreCharacteristic()

• class Mammal
• public void printCharacteristic()
• System.out.println("Warm Blooded")
• class Man extends Mammal
• public void printCharacteristic()
• System.out.println("Warm Blooded and is
  intelligent")
• public void printMoreCharacteristic()
• System.out.println("Can code in Java!")

A man is a subclass of a mammal, hence a man is a
mammal. Is mammal a man ?
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Question 1

• 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

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Question 1

• 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.

10
Question 1

• 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

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Question 1 - UserInterface

• 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

12
Question 1

• class Minesweeperboolean hasWon()
• boolean hasLost()
• String getTileString(int x, int y)
• int getMineCounter()

13
Question 1

• 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?

14
Question 1

• 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)

15
Question 1

• Right click
• Toggles the flag status on a tile if it is not
  uncovered yet

16
Question 1

• 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)

17
Question 1

• 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!

18
Question 1

• For example boolean isUncovered(int x, int y)
• Algorithm Go to the gridxy to access the
  tile, and ask the tile if it is uncovered.
• Hence Tile needs a isUncovered() method!

19
Question 1

• class Tile
• int toggleFlag()
• void uncover()
• public boolean isUncovered()
• public string getTileString()
• bool isMine()

20
Question 1

• Why is getNeighborMines() in the Minesweeper
  class instead of the Tile class ?
• The tiles do not store its neighbors indices!
  But the Minesweeper class knows! (Because an
  array is used to store all the tiles)

21
Question 1

• 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.

22
Question 1

• Lets take a look at the command line version of
  the game!

23
Question 2

• About Java defined ADTs
• To give you some idea of how a good ADT should
  abstract implementation details from its users!

24
Question 2

• class ClassList
• private ArrayListltStringgt cl
• public ClassList()
• cl new ArrayListltStringgt()
• public void add(String name)
• cl.add(name)
• public void delete(String name)
• for(int i 0 i lt cl.size() i)
• String comparedName cl.get(i)
• if(comparedName.equals(name))
• cl.remove(i)

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Question 2

• class ClassList
• private VectorltStringgt cl
• public ClassList()
• cl new VectorltStringgt()
• public void add(String name)
• cl.add(name)
• public void delete(String name)
• for(int i 0 i lt cl.size() i)
• String comparedName cl.get(i)
• if(comparedName.equals(name))
• cl.remove(i)

26
Question 2

• Both Vector and ArrayList inherits from
  AbstractList with defined add and delete methods!
• Does your method names and parameters have to
  change when you change your underlying data
  structure?
• For the Array Implementation, we move on to
  question 3 as it is similar

27
Question 3

• Poses the challenges when writing an ADT

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Question 3

• With an underlying data structure to be an array
  what size will your array be?
• What happens when you remove and element in the
  middle of the array?
• What happens when the array is full?

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Question 3

• Removing an element from the middle of the array
• You would have to push the elements at the back
  to fill up the gap!

Size() 8
Size() 7
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Question 3

• When array is full
• Create a new array with twice the size of the old
  one and copy all the old data into the larger
  array
• Hard coding a limit is not acceptable!

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Question 4

• 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

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Question 4

• Lets look at how it is stated in your mobile
  phone manual..

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Question 4

• Dial the sequence of numbers, and press the green
  call button. If call succeeds you will see the
  connected word on your screen.

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Question 4

• How to dial a number
• callNumber(int x)
• //Input a number
• //Output boolean //representing connection
  //success or failure

35
Question 4

• Does your manual tell you the details of how it
  works?

36
Question 4

• On entering the number, the number is stored as a
  string. The numbers are first checked for country
  code using a stringtokenizer to tokenizer into
  three tokens and then and finally if there
  are no problems, the connected word is displayed

37
Question 4

• How to dial a number
• callNumber(int x)
• //Input a number
• //When the number is passed, it //is stored as a
  string, the //numbers are checked for area //code
  using a stringtokenizer //to tokenize into 3
  tokens //representing..

BAD!!!
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Question 4

• Are you really interested to know the details?
• You just want to make a call!
• And that is the purpose of an ADT to allow the
  users to use it without caring about the
  implementation details!