1. Objects as a programming concept
IB Computer Science

2. HL Topics 1-7, D1-4 1: System design 2: Computer Organisation
3: Networks
4: Computational thinking
5: Abstract data
structures
6: Resource
management
7: Control
D: OOP

3. HL & SL D.1 Overview 1: System design 2: Computer Organisation
3: Networks
D.1 Objects as a programming concept
D.1.1 Outline the general nature of an object
D.1.2 Distinguish between an object (definition, template or class) and instantiation
D.1.3 Construct unified modelling language (UML) diagrams to represent object designs
D.1.4 Interpret UML diagrams
D.1.5 Describe the process of decomposition into several related objects
D.1.6 Describe the relationships between objects for a given problem
D.1.7 Outline the need to reduce dependencies between objects in a given problem
D.1.8 Construct related objects for a given problem
D.1.9 Explain the need for different data types to represent data items
D.1.10 Describe how data items can be passed to and from actions as parameters
4: Computational
thinking
5: Abstract data structures
6: Resource management
7: Control
D: OOP

4. Topic D.1.1
Outline the general nature of an object

5. Definition: object An object is a ‘thing’.
An object is an abstract entity.
It has two components: data and actions.

7. Object & Class
Object - Objects have states (variables) and behaviors (methods). Example: A dog has states - color, name, breed as well as behaviors -wagging, barking, eating. An object is an instance of a class.
Class - A class can be defined as a template/blue print that describes the behaviors/states that object of its type support.

8. etc. All these objects have a state and behavior.
Real world vs Software
What are real-world objects? Cars, Dogs, Humans,
etc. All these objects have a state and behavior.
If we consider a dog, then its state is - name, breed, color, and the behavior is - barking, wagging, running
Software objects also have a state and behavior. A software object's state is stored in fields and behavior is shown via methods.

9. Example:
Fields
States
Methods
Behaviours

10. Constructors Every class has a constructor.
Each time a new object is created, at least one constructor will be invoked (called/run).
The main rule of constructors is that they should have the
same name as the class.
A class can have more than one constructor.

11. Steps in object creation:
A class provides the blueprints for objects.
An object is created from a class.
In Java, the new key word is used to create new objects.
There are three steps when creating an object from a class:
Declaration: A variable declaration with a variable name with an object type.
Instantiation: The 'new' key word is used to create the object.
Initialization: The 'new' keyword is followed by a call to a
constructor. This call initializes the new object.

12. Example:
Output:

13. Summary of code

14. Output:

15. We tend to split classes
Many methods
Object
Class
main()
Running
Class

16. Output:

17. Summary – key terms Think Pair Share Object Class State Behaviour
Field
Method
Constructor
Declaration
Instantiation
Initialization
Think
Pair
Share