CS1102 Tutorial

1
CS1102 Tutorial

• Max Tan
• tanhuiyi_at_comp.nus.edu.sg
• COM1-01-09 Tel[phone]

2
about myself

• Graduated in 2006 in Computer Science
• Final Year Masters Student
• Research in Protein Sequencing
• Completed all his modules, but just a student
  like yourself!
• So, please dont call me Mr. Tan or Sir, call me
  Max (Im still young)

3
about myself

• Consultation hours Tuesday 2 - 4 in my office
  COM1 01-09
• Or you can make an appointment with me via email
• You may download tutorials, answers and this
  slides at http//www.comp.nus.edu.sg/tanhuiyi/

4
about cs1102

• Disclaimer All statements are my own opinions as
  a fresh grad from SoC
• Probably the 2nd toughest module after cs1231
  (dont worry!)
• Requires a strong grasp of programming in Java.
  This is not a Java introductory course

5
about cs1102

• Prereqs A pass in CS1101
• However, that is highly misleading, the module
  requires a very strong understanding of CS1101.
• Lectures will assume you can code anything that
  has been taught in CS1101
• All modules taught in the earlier topics will be
  used in the later topics, and it is assumed that
  you know the earlier topics

6
about cs1102
ADTs
LinkedLists
Queues
Stacks
Hashing
Trees
Graphs
A rough view of how the syllabus is related
Sorting
Complexity
7
about cs1102

• This is not an easy module
• Try to catch up, if you lag behind in one topic,
  you will not be able to understand the next
• Lets look at some past student feedback

8
student feedback

• Lecturer has put in effort so that we can spend
  reasonable time on lab exercises and also take
  care of other modules. However, the module on the
  whole is still difficult.
• i personally dislike programming. So this module
  is just too difficult for me.
• as one of the most tough moudule in SOC, the
  structure of the course is not well
  designed.especally the weekly lab assignment,
  from which hardly anything can be learned. some
  important concepts are not well clarified in
  lectures.
• This module is known as one of the most diffcult
  modules that offered in SOC. It absolutely
  requires a lot of hard wording.
• Well it's a nice module. Tough and challenging.
• This module is too heavy. The cirriculum is
  amazing and the weekly lab assignments are too
  difficult. It takes students so much time to do
  them weekly tha syudents neglect other subjects.
• More time should be taken to teach this. Too much
  content in too little time.

9
about cs1102

• Not trying to scare you off
• Help is at hand!
• Your two lecturers, Dr Tan and Prof Ling
• Your three tutors, myself, Hugo, Zhangli

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CA

• Labs 20
• tutorial participation 5
• Midterm test 20 (closed book)
• Practical exam 15
• Exam 40  (closed book)

11
CA

• tutorial participation 5
• Ask/Answer questions/chat with me/present
  solution/prove your existence to gain the 5
  marks.
• At the end of the semester, if I can remember
  your name, you get 5 P

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how to do well for cs1102

• Attend all lectures.
• Attempt all tutorials by yourself and attend all
  tutorials
• Attempt the labs by yourself.
• For all of the above, do not seek help until you
  have spent a good amount of time thinking through
  problems!
• Make sure you are up to date with all materials,
  if you need some clarifications, look for me

13
how to do well for cs1102

• If you get lost in the earlier lectures, please
  work to understand and look for me for help.
• The later portions of the course are heavily
  dependent on the earlier parts.

14
tutorial format

• First 15 minutes Brief overview by me on some
  difficult lecture materials
• Next 40 minutes Tutorial question presentations
  you talk. I listen.
• You will split into 4 groups (for the entire
  semester) and present your solutions as a
  grp/individual (to your preference)
• Remaining time further questions (usually no
  remaining time)

15
tutorial format

• Today
• Group 1 Question 1 and 5
• Group 2 Question 2 and 6
• Group 3 Question 3 and 4
• Group 4 Question 7
• Next week, Group 1 Q2, Group 2 Q3, Group 3
  Q4, Group 4 Q1 (add 1 to your question number
  every week)

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CS1102 Tut 1 Java Revisit

• Max Tan
• tanhuiyi_at_comp.nus.edu.sg
• COM1-01-09 Tel[phone]

17
15 minute recap

• List of List of String
• ArrayList lt ArrayList ltStringgt gt bigBox new
  ArrayList lt ArrayList ltStringgt gt()
• How do I access, use, or read the above
  complicated-as-hell statement?
• ArrayList lt ArrayList ltStringgt gt bigBox
• Means that this is an ArrayList object, with the
  identifier bigBox
• Means that the type stored in the ArrayList
  object is a ArrayList ltStringgt

18
15 minute recap

• Meaning whatever we put into bigBox must be of
  type ArrayList ltStringgt
• E.g.
• ArrayList ltStringgt smallBox new
  ArrayListltStringgt()
• bigBox.add(smallBox) is valid
• String candy mms
• bigBox.add(candy) is NOT valid

19
15 minute recap

• List of List of String
• Imagine a Box as a List

candy
SmallBox
BigBox lt SmallBoxltcandygt gt ArrayList lt
ArrayListltStringgt gt
BigBox
20
15 minute recap

• Can you access the candy items from the BigBox ?
• No! You have to take out the SmallBox first
  before you can access the candy!

candy
SmallBox
SmallBox s bigBox.get(0) Candy c s.get(0)
BigBox
21
q1

• Let the initial values of x and y be 1 and 2 for
  questions a to e below. What is the value of z
  after the following operations?
• z x y
• z x y
• z x y
• z x --y
• z x y

22
q1

• xmeans add to the value of x BEFORE running
  the operation x appears in
• xmeans add to the value of x AFTER running the
  operation x appears in
• Basically y x 1can be rewritten asx
  x1y x 1

23
q1

• x 1, y 2
• z x y (3)
• z x y (4)
• z x y (4)
• z x --y (3)
• z x y (5)

24
q2

• Methods to mutate and access the private
  variables of a class are called mutators and
  accessors respectively. List the possible
  mutators and accessors of a Triangle class. You
  may assume your own definition of the data fields
  in the class.

25
q2

• What can you do to a triangle ?
• Mutators
• Set the lengths of the sides setLength(int side,
  int length)
• Set the angles setAngle(int side, int angle)
• Accessors
• Get the angles getAngle(int side)
• Get the lengths getLength(int side)

26
q3 q4

• What is information hiding and encapsulation? How
  does Java support these concepts?
• How is code reuse supported in Java?

27
q3 q4

• Information hiding makes implementation details,
  including components of an object, inaccessible
• Implemented in Java by private and protected
  keywords
• Encapsulation is the grouping of data and the
  operations that apply to them to form an
  aggregate while hiding the implementation of the
  aggregate
• Implemented in Java by classes
• Code reuse is supported by Java through the use
  of class inheritance (the extends keyword)

28
q5

• 1 class Person
• 2
• 3 public static final int NO_SSN -1
• 4
• 5 private int SSN 0
• 6 String name null
• 7
• 8
• 9 class TestPerson
• 10
• 11 private Person p new Person()
• 12
• 13 public static void main(String args)
• 14
• 15 Person q new Person()
• 16
• 17 System.out.println(p)
• 18 System.out.println(q)
• 19

• Line 17 is illegal, even though line 18 is legal.
  Explain why.

29
q5

• p is declared in the TestPerson class context
• p does not have a static keyword
• You cannot access a non-static object/variable in
  a static scope (in this case the main method)
• BUT you can access a static object in a
  non-static scope!
• You need to understand that when the static
  keyword is used, regardless of how many instances
  of the object exists, there is only ONE common
  object corresponding to that static variable

30
q5

• 1 class Person
• 2
• 3 public static final int NO_SSN -1
• 4
• 5 private int SSN 0
• 6 String name null
• 7
• 8
• 9 class TestPerson
• 10
• 11 private Person p new Person()
• 12
• 13 public static void main(String args)
• 14
• 15 Person q new Person()
• 16
• 17 System.out.println(p)
• 18 System.out.println(q)
• 19

• Which of lines 20 to 24 are legal and which are
  not? Explain why.

31
q5

• Line 20 and 23 are legal as NO_SSN is a public
  static field which can be accessed via an object
  reference or a class name
• Line 22 is legal because by default, name is
  visible
• Line 21 and 24 are illegal because SSN is
  private. Also, Person.SSN is illegal as SSN is
  nonstatic.)

32
q6

• 1 public class Base
• 2
• 3 public int bPublic
• 4 protected int bProtext
• 5 private int bPrivate
• 6 // Public methods follow
• 7
• 8
• 9 public class Derived extends Base
• 10
• 11 public int dPublic
• 12 private int dPrivate
• 13 // Public methods follow
• 14
• 15
• 16 public class Tester
• 17
• 18 public static void main(String args)
• 19

• Which accesses are illegal?

33
q6

• 1 public class Base
• 2
• 3 public int bPublic
• 4 protected int bProtect
• 5 private int bPrivate
• 6 // Public methods follow
• 7
• 8
• 9 public class Derived extends Base
• 10
• 11 public int dPublic
• 12 private int dPrivate
• 13 // Public methods follow
• 14
• 15
• 16 public class Tester
• 17
• 18 public static void main(String args)
• 19

• Which accesses are illegal?
• You can only access b.bProtect IF and ONLY IF
  they are in the same package

34
q6

• 1 public class Base
• 2
• 3 public int bPublic
• 4 protected int bProtect
• 5 private int bPrivate
• 6 // Public methods follow
• 7 public static void main(String args)
• 8
• 9 Based b new Base()
• 10 Derived d new Derived()
• 11
• 12 System.out.println(
• 13 b.bPublic " " b.bProtect " "
• 14 b.bPrivate " " d.dPublic " "
• 15 d.dPrivate)
• 16
• 17
• 18
• 19 public class Derived extends Base

b. Make main a method in Base. Which accesses
are illegal?
35
q6

• 1 public class Base
• 2
• 3 public int bPublic
• 4 protected int bProtect
• 5 private int bPrivate
• 6 // Public methods follow
• 7 public static void main(String args)
• 8
• 9 Based b new Base()
• 10 Derived d new Derived()
• 11
• 12 System.out.println(
• 13 b.bPublic " " b.bProtect " "
• 14 b.bPrivate " " d.dPublic " "
• 15 d.dPrivate)
• 16
• 17
• 18
• 19 public class Derived extends Base

• b. Make main a method in Base. Which accesses
  are illegal?
• Ans Only d.dPrivate is illegal
• Why can you access b.bPrivate ?
• Recall in lecture notes -gt
• Private members can be accessed by methods of the
  class.
• Now you can definitely access b.bProtect

36
q6

• 1 public class Base
• 2
• 3 public int bPublic
• 4 protected int bProtect
• 5 private int bPrivate
• 6 // Public methods follow
• 7
• 8
• 9 public class Derived extends Base
• 10
• 11 public int dPublic
• 12 private int dPrivate
• 13 // Public methods follow
• 14 public static void main(String args)
• 15
• 16 Based b new Base()
• 17 Derived d new Derived()
• 18
• 19 System.out.println(

c. Make main a method in Derived. Which
accesses are illegal?
37
q6

• 1 public class Base
• 2
• 3 public int bPublic
• 4 protected int bProtect
• 5 private int bPrivate
• 6 // Public methods follow
• 7
• 8
• 9 public class Derived extends Base
• 10
• 11 public int dPublic
• 12 private int dPrivate
• 13 // Public methods follow
• 14 public static void main(String args)
• 15
• 16 Based b new Base()
• 17 Derived d new Derived()
• 18
• 19 System.out.println(

• Make main a method in Derived. Which accesses are
  illegal?
• Only b.bPrivate is illegal, all others are legal
  as it is not in the same class

38
q6

• d. How do these answers change if protected is
  removed from protected int bProtect?

39
q6

• d. How do these answers change if protected is
  removed from protected int bProtect?
• Ans If the classes are in the same package, then
  it is visible in all cases stated above
  OTHERWISE, first case NO, second and third case
  YES
• By default, if you do not specify a accessibility
  modifier, it will be package-private i.e. same
  accessibility as protected EXCLUDING subclass

40
q6

• e. Write a three parameter constructor for Base.
  Then write a five parameter constructor for
  Derived.

41
q6

• e. Write a three parameter constructor for Base.
  Then write a five parameter constructor for
  Derived.
• Ans Base(int pub, int pri, int pro)
• bPublic pub bPrivate pri bProtext pro
• Derived(int bpub, int bpri, int bpro, int dpub,
  int dpri)
• super(bpub, bpri, bpro)
• dPublic dpub dPrivate dpri

42
q6

• f. The class Derived consists of 5 integers.
  Which are accessible to the class Derived?

43
q6

• f. The class Derived consists of 5 integers.
  Which are accessible to the class Derived?
• Ans all except bPrivate as Derived is a subclass
  of Base

44
q6

• g. A method in the class Derived is passed a Base
  object. Which of the Base object members can the
  Derived class access?

45
q6

• g. A method in the class Derived is passed a Base
  object. Which of the Base object members can the
  Derived class access?
• Ans all except bPrivate as Derived is a subclass
  of Base