CS 46B - Lecture 1

Cover page image

Cay S. Horstmann

CS 46B

Second course in computer science
Learn about algorithms and data structures
Learn good software engineering habits
For green sheet, contact information, etc., see http://horstmann.com/sjsu/fall2015/cs46b

Active Learning

Changing the brain

No couch potatos!
You read the book before class
Exercises during lectures
You need your laptop for every lecture
Mandatory lab
You fail the class if you don't do the lab
Lots of homework
You only learn by doing
You only learn if you do it yourself

What You Need to Succeed

Prerequisites: CS1 in Java

Completion or concurrent enrollment in discrete math

Your Responsibilities

Come to every class meeting
- And come to every lab meeting
Do the assigned reading (and the quiz) before class.
- I won't lecture on the material that you can read yourself
Submit two versions of each programming assignment
- I don't want you to start working the day before the due date
Spend 12 hours per week for this class
- 2.5 hours in class
- 2.5 hours in the lab
- 7 hours (!) for preparation and homework
Ask questions right away when you are stuck
- Use the online discussion group. You'll get a better grade if you ask lots of questions.
- Answer your peers' questions. You'll get a better grade if you do.
- Private or confidential questions—email or office hours

Homework

Homework is due before every class meeting
Every Tuesday and Saturday 6 pm
Grace period for uploading until 11:59 pm
- Don't rely on it—get it done by 6 pm
- No mercy after midnight
You submit to Canvas
Programming assignments in two stages
- Draft: Something that does a part of the job (must compile)
- Final: The complete solution
Sometimes, you need to upload an image too (such as in homework 1)

Lab

You must register for a lab section
You must attend the lab sections in order to pass the class
- Lab grade F ⇒ course grade F
- Lab grade A - D counts for 5% of the course
Bring your laptop to the lab
You will work with a buddy
One of you writes code, the other types up answers
Switch roles each week
If your lab is scheduled for Tuesday, your first session is tomorrow

The Textbook

Read the textbook before each class meeting
Bring the textbook to class and labs
You need the book now
You need the correct edition (7th edition of Java Concepts or 5th edition of Big Java)
The college bookstore has a slightly discounted custom edition for SJSU
An ebook is fine (I recommend this version)
Do not get an “international edition”—it is different.

Adding

Do the prerequisite quiz and send me your answers.
I will send you an add code when space becomes available. Use it within 24 hours, or it will become invalid
Show up for all classes/labs even if you haven't received your code
You MUST register for the lab that I assign to you, or you will be instructor-dropped from both the course and the lab
In the meantime, respond to the invitation in Canvas/Piazza and do all the work
You'll have to do the lab work on your own until you have an add code

Things To Do Today

Log into Canvas and Piazza
Upload a photo into your profile so I know who you are
Get the textbook and start reading it
Get a laptop and install the virtual machine for the course
Look at Quiz 1 and Homework 1 draft in Canvas
Important: In lieu of a roll call today, you must turn in Homework 1 draft by the deadline, or I will drop you from this course for lack of presence.

Inheritance Hierarchies

Inheritance: the relationship between a more general class (superclass) and a more specialized class (subclass).
The subclass inherits data and behavior from the superclass.
Cars share the common traits of all vehicles
- Example: the ability to transport people from one place to another

Inheritance Hierarchies

The class Car inherits from the class Vehicle
The Vehicle class is the superclass
The Car class is the subclass

Inheritance Hierarchies

Inheritance lets you can reuse code instead of duplicating it.
Two types of reuse
- A subclass inherits the methods of the superclass
- Because a car is a special kind of vehicle, we can use a Car object in algorithms that manipulate Vehicle objects
The substitution principle:
- You can always use a subclass object when a superclass object is expected.
A method that processes Vehicle objects can handle any kind of vehicle

Lecture 1 Clicker Question 1

Consider the method doSomething(Car c). Name the class whose objects cannot be passed to this method.
vehicle hierarcy

Car
Sedan
SUV
Vehicle

Inheritance Hierarchies

Example: Computer-graded quiz

There are different kinds of questions
A question can display its text, and it can check whether a given response is a correct answer.
You can form subclasses of the Question class.

question hierarchy

Implementing Subclasses

To get a ChoiceQuestion class, implement it as a subclass of Question
- Specify what makes the subclass different from its superclass.
- Subclass objects automatically have the instance variables that are declared in the superclass.
- Only declare instance variables that are not part of the superclass objects.
A subclass inherits all methods that it does not override.

Implementing Subclasses

The subclass inherits all public methods from the superclass.
You declare any methods that are new to the subclass.
You change the implementation of inherited methods if the inherited behavior is not appropriate.
Override a method: supply a new implementation for an inherited method

Implementing Subclasses

A ChoiceQuestion object differs from a Question object in three ways:

Its objects store the various choices for the answer.
There is a method for adding answer choices.
The display method of the ChoiceQuestion class shows these choices so that the respondent can choose one of them.

Implementing Subclasses

UML of the ChoiceQuestion

The ChoiceQuestion class needs to spell out the three differences:

public class ChoiceQuestion extends Question
{
   // This instance variable is added to the subclass
   private ArrayList<String> choices;
   
   // This method is added to the subclass
   public void addChoice(String choice, boolean correct) { . . . }
   
   // This method overrides a method from the superclass
   public void display() { . . . }
}

The extends reserved word indicates that a class inherits from a superclass.

Implementing Subclasses

A ChoiceQuestion object
You can call the inherited methods on a subclass object:
```
choiceQuestion.setAnswer("2");
```
The private instance variables of the superclass are inaccessible.
The ChoiceQuestion methods cannot directly access the instance variable answer.
ChoiceQuestion methods must use the public interface of the Question class to access its private data.

Implementing Subclasses

Adding a new method: addChoice

public void addChoice(String choice, boolean correct)
{
   choices.add(choice);
   if (correct)
   {
      // Convert choices.size() to string
      String choiceString = "" + choices.size();
      setAnswer(choiceString);
   }
}

addChoice method can not just access the answer variable in the superclass:
It must use the setAnswer method

Invoke setAnswer on the implicit parameter:

setAnswer(choiceString);

this.setAnswer(choiceString);

Lecture 1 Clicker Question 2

Which of the following statements is true?

Question is a subclass of ChoiceQuestion
The ChoiceQuestion class overrides the setText method of Question
The ChoiceQuestion class inherits the checkAnswer method of Question
The ChoiceQuestion method inherits the display method of Question

Lecture 1 Clicker Question 3

Suppose q is an object of the class Question and cq an object of the class ChoiceQuestion. Which of the following calls is not legal?

q.setAnswer(response)
cq.setAnswer(response)
q.addChoice(choice, true)
cq.addChoice(choice, true)

Before Next Class

Read sections 9.3 - 9.5, Special Topics 9.1, 9.2 and How To 9.1 of your textbook
Make sure to do the quiz
Tuesday lab starts tomorrow
Make sure you do homework 1 draft—or you will be dropped