2.1 Introduction to ObjectOriented Programming
2.1.1 Procedural versus OOP
languages
• Procedural programming involves
creating a sequence of instructions
• OOP uses a collection of
interacting objects
• Functions are logically grouped,
making enhancements easy
• OOP can model human problemsolving
2.1.2 Basic Java terminology
Object. contains data and instructions
Class. blueprint for an object
Attribute. describe the state of objects
Data Type. describes what kind of information a
certain attribute is
Behavior. describe what objects can do
Method. a set of instructions
Inheritance. Some objects derive attributes and
behaviors from other objects
Encapsulation. Combining data and methods
together
2.2 What are Objects? 2.2.1
Introduction to objects
• Anything tangible or abstract that is
relevent
• Objects can have attributes and
behaviors
• Attributes describe the object
• Behaviors describe what the object
can do
2.2.2 Classification of objects
• User Interface objects
– Objects that the user interacts directly
with
• Operating environment objects
– Provide services to other components
• Task Related objects
– Documents, multimedia, problem
domain
2.2.3 Objects - identifying, defining,
creating and operating on
• Identifying – Requires needs assessment
• Defining – Classification, relationships,
operations. The class keyword
• Creating – The constructor and the new
keyword
• Operating – Using an object’s methods
2.2.7 Encapsulation
• To hide the details, package together
• Access modifiers – public, private
and protected
2.2.8 Object relationships
• Association
– Objects know
about each other
• Whole-part
– Existance of an
object relies on
another
• Inheritance
– Attributes &
behaviors can be
inherited
2.2.9 Inheritance
2.2.10 Object mutability and
destruction
• Some object attributes should be immutable, or
unchangable
• To make an item immutable, use the final
keyword
• The JVM automatically releases memory when
objects are no longer required
• The garbage collector will reclaim memory by
objects that are no longer referenced
• Garage collection is not controllable
2.3.1 Modeling languages and
symbols
• Unified Modeling
Language (UML)
standardizes symbols
& terminology for
diagramming objects
2.3.2 Basic Class symbol
• Rectangle represents a class
of objects
• 3 compartments: Name,
attributes , and operations or
methods
• Symbols indicate
accessibility
2.4.1 Class definition
public class Person {
private String name;
public Person(String theName) {
name = theName;
}
}
•Defined by using
the class keyword
•Public classes
defined in separate
files
•Filename must be
the same as the
class name
2.4.2 Creating objects
• Constructor methods are called when an
object is created
• All object data is stored in memory
• Variables are a reference to the memory
location
2.4.3 Object methods
•
•
•
•
•
Mutator – Changes object data
Accessor – Retrieves object data
Methods with no arguments
Methods that require arguments
Method return values – Provide a result to
the caller
2.5.1 System class
• Data stored by an object is member data
• Data present in an object’s methods is
called local or temporary data
• Java.lang.System is a pre-defined object
that can be used to perform system tasks
System.out.println(“Hello World!”);