1. Can perform actions and provide communication
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Chapter 7 Objects
A variable of a data type that is a class. Also called an instance of a class.
Stores data
Can perform actions and provide communication
State of object refers to the data it stores
Behavior of object refers to the action and communication it provides
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2. Used to create, or instantiate, objects
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Chapter 7 Class
An abstract data type
Used to create, or instantiate, objects
Provides encapsulation, also called information hiding
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3. Chapter 7 The Circle Class
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Chapter 7 The Circle Class
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4. access level class name body variables constructor method
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Chapter 7 A Class
access level
class name
body
public class Circle { private static final double PI = 3.14; private double radius; public Circle() { radius = 1; } public void setRadius(double newRadius) { radius = newRadius; }
variables
constructor
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A class declaration includes an access level. <press space bar> The keyword public is called an access modifier. A public class is visible to other classes.
Class names should be a noun. <press space bar> A class name should begin with an uppercase letter and then an uppercase letter should also begin each word within the name.
The body of the class starts with the first opening brace and ends with the matching closing brace. <press space bar>
Within the body of a class are the members of the class. The variables of the class are declared first. <press space bar> The visibility of the member variables is controlled with access modifiers. Declaring a variable as private makes it visible to the class, but not to client code. This encapsulates the data and provides and provides information hiding. Variables define the state of an object.
A class has at least one constructor. <press space bar> A constructor is automatically called when an object is created. The constructor is where variables are initialized.
A class can have several methods. <press space bar> Methods define the behavior of an object.
method
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5. Chapter 7 Methods in a Class
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Chapter 7 Methods in a Class
An accessor method is used to determine the value of a variable
A modifier method is used to change the value of a variable
A helper method is called from within a class by other methods
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6. Chapter 7 Overloading Constructors
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Chapter 7 Overloading Constructors
Constructors can be overloaded to provide more options for instantiating an object
The compiler uses the number and types of parameters to determine which constructor to execute
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7. Chapter 7 Instance and Class Variables
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Chapter 7 Instance and Class Variables
Each object of a class has its own copy of the instance variables in the class.
A class variable is declared with the keyword static and only one copy of a class variable is maintained for all objects to refer to. Circle spot1 = new Circle(2); radius PI Circle spot2 = new Circle(5); radius PI 2
3.14 5
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8. Chapter 7 Instance and Class Methods
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Chapter 7 Instance and Class Methods
Instance methods must be called from an instance of the class. Accessor and modifier methods are always instance methods because they change the state of an object.
Class methods are declared using the keyword static and can be called from the class itself.
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9. Chapter 7 Differences Between Instance and Class Members
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Chapter 7 Differences Between Instance and Class Members
Instance variables are created each time an object is declared.
Class variables are created once for the class and then objects of the class refer to this copy.
Instance methods can only be called from an object of the class.
Class methods can be called from the class itself.
© 2012 EMC Publishing, LLC

10. Chapter 7 The Object Class
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Chapter 7 The Object Class
Superclass of all other classes. Classes, such as Circle and String, are subclasses:
All subclasses inherit the Object methods, which include equals() and toString().
Inherited superclass methods can be redefined, or overridden, in subclasses.
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11. Chapter 7 Classes Using Classes
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Chapter 7 Classes Using Classes
A class containing a member variable that is a class data type.
Demonstrates a has-a relationship. The class "has-a" class.
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12. Chapter 7 Object-Oriented Development
Objects are selected to model a program specification
Objects are created from new classes or from existing classes
Objects send messages to other objects to perform a task
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13. Chapter 7 Features of Object-Oriented Programming
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Chapter 7 Features of Object-Oriented Programming
Reusability: existing classes can be used over and over again in different applications, which reduces development time and decreases the likelihood of bugs.
Modular: Components are separately written and maintained.
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