• objects
• classes
• methods
• parameters
• data types
• fields
• constructors
• accessor methods 
• mutator methods
• assignment
• conditional statement
• local variables
• instance variables
• boolean
• integer
• string
• variable

Refining Your Understanding of Classes and Objects

When you program in Java, you work constantly with classes and objects. These two ideas are really important.

Close your eyes for a minute and think about what it means for something to be a chair.

A chair has a seat, a back, and legs. Each seat has a shape, a color, a degree of softness, and so on. These are the properties that a chair possesses. What is described is chairness — the notion of something being a chair. In object-oriented terminology, this describes the chair class.

Now take a minute to look around your room. (If you're not sitting in a room right now, fake it.)

Several chairs are in the room, and each chair is an object. Each of these objects is an example of that ethereal thing called the Chair class. So that's how it works — the class is the idea of chairness,and each individual chair is an object.

A class isn't quite a collection of things. Instead, a class is the idea behind a certain kind of thing. When we talk about the class of chairs in your room, we're talking about the fact that each chair has legs, a seat, a color, and so on. The colors may be different for different chairs in the room, but that doesn't matter. When you talk about a class of things, you're focusing on the properties that each of the things possesses.

It makes sense to think of an object as being a concrete instance of a class. In fact, the official terminology is consistent with this thinking. If you write a Java program in which you define a Chair class, each actual chair (the chair that you're sitting on, the empty chair right next to you, and so on) is called an instance of the Chair class.

Here's another way to think about a class. Imagine a table displaying all three of your bank accounts. (See Table 1.)

Table 1 A Table of Accounts

Think of the table's column headings as a class, and think of each row of the table as an object. The table's column headings describe the Account class.

According to the table's column headings, each account has an account number, a type, and a balance. Rephrased in the terminology of object-oriented programming, each object in the Account class (that is, each instance of the Account class) has an account number, a type, and a balance. So, the bottom row of the table is an object with account number 16-17238-13344-7. This same object has type Savings and a balance of 247.38. If you opened a new account, you would have another object, and the table would grow an additional row. The new object would be an instance of the same Account class.

In Class Demonstration

Dog Class:

All dogs have 4 legs, ears, a tail, eyes, nose, fur, canine teeth, etc.

Your dog has:

Colour: ‘Gold’ <- String

Name: ‘Chelsea’ <- String

WeightLBS: 20 <- int

Breed: ‘Lab’ <-String

Male/Female: ‘Female’ <- String

IsNeutered?: No <-Boolean

Strings – combination of letters

Integers - numbers

Floating Points – decimal numbers

Boolean – yes or no answer

In Class we viewed the Chapter 1 Power Point

Read through Chapter 1 and completed the activities

Analyzed this Dog Class

Began activity 1

Work with a partner. For this lab you will begin to create a class called Student. Here are the

attributes of a student that we are concerned with for the purpose of this project:

 first name

 last name

 student number, e.g. A00012345

 email address

 number of courses completed

 grade, e.g. 78.5

 is the student in good standing? true or false

Choose appropriate data types and descriptive names for the fields (instance variables), and

declare them. Be sure to specify that they are private.

Write a constructor for this class. The constructor will expect all the information to be passed in

as parameters. Choose descriptive names for the parameters but remember that they cannot be

the same as the field names. Use the parameters to initialize the fields.

Test your project by creating a Student object. Use the BlueJ inspector to check the contents of

the fields.

Be sure both partners have a copy of the completed project.

Due end of class on Thursday

Grade 12  Assignment: Guessing Game - due end of class on Thursday

An accessor is a method that accesses the contents of an object but does not modify that object. In the simplest case, an accessor just returns the value of one of the fields. In general, an accessor performs some computation using the fields as long as that computation does not modify any of the fields.

A mutator is a method that can modify an object. In the simplest case, a mutator just assigns a new value to one of the fields. In general, a mutator performs some computation and modifies any number of fields.

Sometimes, accessors are called 'getter' methods and mutators are called 'setter' methods.

Task: add a mutator method to each object in the "Student Class"

---

Assignment - Cell Phone Class

For this lab you will begin to create a class called CellPhone. Here are the attributes of a cell

phone that we are concerned with for the purpose of this project:

 brand, e.g. Sony Ericson

 model, e.g. W200a

 weight in grams

 megabytes of memory, e.g. 25

 lines of text, e.g. 5 (if this doesn't apply to your phone - add a field for "Does it have a touchscreen?")

 does it have a camera?

 does it have an alarm clock?

 does it have games?

 does it vibrate?

Choose descriptive names for the fields (instance variables) and declare them. Be sure to specify

that they are private.

Write a constructor for this class. The constructor will expect all the information to be passed in

as parameters. Choose descriptive names for the parameters but remember that they cannot be

the same as the field names. Use the parameters to initialize the fields.