IB Computer Science Topic D.1.4 Relationships Between Objects Revision Notes (SL/HL)

IB Computer Science Topic D.1.4 Relationships Between Objects Revision Notes (SL/HL) | RevisionDojo

Understanding Relationships Between Objects

In object-oriented programming (OOP), relationships between objects are fundamental to designing flexible and maintainable systems.

These relationships define how objects interact, collaborate, and depend on each other to solve complex problems.

Key Relationships in OOP

Dependency ("uses")
Aggregation ("has-a")
Inheritance ("is-a")

Example

Imagine a traffic simulation model:

Vehicle: Have subclasses CityCar and LargeTruck (inheritance).
TrafficLight: Uses a Timer to control signals (dependency).
Road: Has multiple Vehicle objects (aggregation).

Let's explore each of these relationships in detail.

Dependency ("Uses-a") Relationship

A dependency relationship occurs when one object relies on another to function.
This is often described as a "uses" relationship.

Dependency can be:

Temporary: The relationship exists only when a specific action is performed.
Unidirectional: One object depends on another, but not necessarily vice versa.

Example

Here, Report depends on Printer to print

Note

In UML diagrams, dependency is represented by a dashed arrow pointing from the dependent class to the class it depends on.

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Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

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Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

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Understanding Relationships Between Objects

In object-oriented programming (OOP), relationships between objects are fundamental to designing flexible and maintainable systems.

These relationships define how objects interact, collaborate, and depend on each other to solve complex problems.

Key Relationships in OOP

Dependency ("uses")
Aggregation ("has-a")
Inheritance ("is-a")

Example

Imagine a traffic simulation model:

Vehicle: Have subclasses CityCar and LargeTruck (inheritance).
TrafficLight: Uses a Timer to control signals (dependency).
Road: Has multiple Vehicle objects (aggregation).

Let's explore each of these relationships in detail.

Dependency ("Uses-a") Relationship

A dependency relationship occurs when one object relies on another to function.
This is often described as a "uses" relationship.

Dependency can be:

Temporary: The relationship exists only when a specific action is performed.
Unidirectional: One object depends on another, but not necessarily vice versa.

Example

Here, Report depends on Printer to print

Note

In UML diagrams, dependency is represented by a dashed arrow pointing from the dependent class to the class it depends on.

Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

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class Printer {
    public void print(String message) {
        System.out.println(message);
    }
}

class Report {
    public void generate() {
        Printer printer = new Printer(); // used temporarily
        printer.print("Report generated");
    }
}

1. System fundamentals2 subtopics

2. Computer organization1 subtopic

3. Networks1 subtopic

4. Computational thinking, problem-solving and programming3 subtopics

5. Abstract data structures (HL)1 subtopic

6. Resource management (HL)1 subtopic

7. Control (HL)1 subtopic

A. Databases4 subtopics

B. Modelling and simulation4 subtopics

C. Web science6 subtopics

D. Object-oriented programming (OOP)4 subtopics

IB Computer Science D.1.4 Relationships Between Objects Notes

1. System fundamentals2 subtopics

2. Computer organization1 subtopic

3. Networks1 subtopic

4. Computational thinking, problem-solving and programming3 subtopics

5. Abstract data structures (HL)1 subtopic

6. Resource management (HL)1 subtopic

7. Control (HL)1 subtopic

A. Databases4 subtopics

B. Modelling and simulation4 subtopics

C. Web science6 subtopics

D. Object-oriented programming (OOP)4 subtopics

Understanding Relationships Between Objects

Key Relationships in OOP

Dependency ("Uses-a") Relationship

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Understanding Relationships Between Objects

Key Relationships in OOP

Dependency ("Uses-a") Relationship

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account