CS1102 Tutorial

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CS1102 Tutorial

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

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about myself

• Graduated last year in Computer Science
• First year PhD candidate
• Research in Protein Sequencing
• Takes 1 module in addition to CS1102
• Just a student like yourself! (No staff
  privileges)
• So, please dont call me Mr. Tan, call me Max

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about myself

• Consultation hours Wed 10 12 in my office s15
  03-07
• Or you can make an appointment with me via email
• You may download tutorials, answers and this
  slides at a link from CS1102 course from
  http//www.comp.nus.edu.sg/tanhuiyi/
• Your turn to introduce!

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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

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about cs1102

• This course is a pre-req to multiple courses in
  Computer science, Computer Engineering and
  Computational Biology
• Multiple sources for you to seek help! mm, Dr
  Tan, the various lab TAs

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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!
• Actively participate in forum discussions. Do not
  post algorithms or answers!

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tutorial format

• First 15 minutes Brief overview on some
  difficult lecture materials
• Next 40 minutes Tutorial question presentations
  you talk. I listen.
• Remaining time further questions

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CS1102 Tut 1 Java Revisit

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

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Question 1

• Parameter passing in methods
• Pass by value or Pass by reference?
• Very important concept that you need to know..
  Used in EVERY aspect of data structures in this
  course

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Question 1

• a.setName(Fred)
• b.setName(Peter)
• changeName_1(a)
• public static void changeName_1(Person a)
• b new Person()
• b.setName("David")
• a b
• //output Fred David

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Question 1
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Question 1
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Question 1

• a.setName(Fred)
• b.setName(Peter)
• changeName_1(a)
• //a.name Fred, b.name David
• changeName_2(a)
• public static void changeName_2(Person a)
• a.setName("John")
• //output John David

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Question 1
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Question 2

• On exception handling and code design
• In general you wont be tested much on exceptions
  in this course.
• How elegant is your program?

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Question 2

• Where did you throw the exception?
• You may try to throw the exception in the code
  before you instantiate the class but what happens
  if you have to instantiate at multiple points of
  the code?
• Better to throw exception at the constructor!

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Question 2

• class IdentityCard
• private int ICNum
• private String name
• public IdentityCard(String ICNum, String name)
  throws InvalidICNumberException
• if(IsInvalidNumber)
• throw new InvalidICNumberException("Invalid IC
  Number.")
• try
• this.ICNum Integer.parseInt(ICNum.substring(1
  ,8))
• catch(Exception e)
• throw new InvalidICNumberException("Non valid
  numerical.")
• this.name name

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Question 2

• How did you check for an invalid number?
• Starts with character s then 7 digits and
  another character.
• How did you check for the last character ?

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Question 2

• Very bad method Use a switch statement for all
  26 letters
• OK method Convert the character to its integer
  representative and check if it falls between
  integer represented by a and z
• Smart method Use Java API
• Character.isDigit(char c)

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Question 3

• On Generic Java Programming
• No emphasis on this in CS1102 either but you need
  to know
• Coursemarker do not like this warning message and
  will fail your test cases if you have them

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Question 3

• import java.util.
• class TestArrayList
• public static void main(Stringargs)
• ArrayListltStringgt v new ArrayListltStringgt()
• v.add("Hello world")

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Question 4

• On method overloading and method overriding
• You will be doing this a lot in this course

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Question 4

• class ContractEmployee extends Employee
• //Some variables and methods here
• //No parameter, indicates fixed monthly pay
• public double computePay()
• //With parameter, indicates hourly pay
• public double computePay(int hoursWorked)
• computePay is overloaded!
• (Two methods with same name, different
  parameters).

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Question 4

• Why method overloading ?
• Consider the sort method which sort indices from
  a start index to a end index in your ADT
  sort(int start, int end)
• You also want a sort method that sort all
  elements in your ADT sort()
• You can simply write the sort method which calls
  the other sort method with two fixed variables!

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Question 4

• Example
• void sort(int start, int end)
• void sort()
• sort(0, list.Length() - 1 )
• Convenience and clarity!

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Question 4

• abstract class Employee
• String name
• public abstract double computePay(int
  hoursWorked)
• class FullTimeEmployee extends Employee
• //Some variables and methods here
• public double computePay(int hoursWorked)
  //
• Overridden!

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Question 4

• Why method overriding?
• Subclasses may perform some actions differently
  from super classes!
• For example if we have a parent class called
  quadrilateral which denotes a set of shapes with
  4 sides and a child class called Square, we want
  to implement the getArea() method differently in
  the child (Square) class!

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Question 4

• Can you instantiate an Employee object?
• No! Employee is an abstract class!
• When we try to set Employee e as a
  ContractEmployee, we call this polymorphism.
• Employee e new ContractEmployee()

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Question 4

• When we try to call the function
  computePay((int)i) as follows
• e.computePay(i)
• At execution time, e is determined to be a
  ContractEmployee object and the method
  implemented by ContractEmployee is used.

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Q n A

• Any questions ?