CST8132 OOP Lecture Notes

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Questions and Answers

What is abstraction in Java?

Hiding implementation details from the user (correct)

Showing implementation details to the user

Displaying the functionality to the user

Providing the implementation details to the user

What is the relationship between a subclass and a superclass?

Composition

Polymorphism

Inheritance (correct)

Abstraction

What is achieved through abstract classes and interfaces in Java?

Abstraction (correct)

Inheritance

Polymorphism

Encapsulation

What is the purpose of abstraction in Java?

To hide implementation details from the user (B) Signup and view all the answers

What is inherited from a superclass to a subclass?

Methods and properties (B) Signup and view all the answers

What is the concept that relates to hiding implementation details in Java?

Abstraction (D) Signup and view all the answers

What is the term for a class that cannot be instantiated?

Abstract class (D) Signup and view all the answers

What is the term for a collection of abstract methods?

Interface (B) Signup and view all the answers

What is the purpose of inheritance in Java?

To inherit properties and methods (B) Signup and view all the answers

What is the relationship between a subclass and a superclass in terms of inheritance?

Many-to-one (A) Signup and view all the answers

What happens when a class includes abstract methods?

The class must be declared abstract. (A) Signup and view all the answers

What is the purpose of an abstract class?

To declare a class that cannot be instantiated. (A) Signup and view all the answers

Can an abstract class be instantiated?

No, it cannot be instantiated. (D) Signup and view all the answers

What happens if a subclass does not provide implementations for all abstract methods?

The subclass will be abstract. (D) Signup and view all the answers

What is the main difference between an abstract class and an interface?

An abstract class has methods with implementation, an interface does not. (D) Signup and view all the answers

What is the purpose of an interface?

To group related methods with empty bodies. (D) Signup and view all the answers

Can an interface have properties?

Yes, an interface can have public static final properties. (C) Signup and view all the answers

What is an example of a situation where an abstract class could be made into an interface?

When an abstract class has nothing other than public static final properties and abstract methods. (C) Signup and view all the answers

What is the purpose of the 'Shape' abstract class in the example?

To provide a blueprint for other shape classes. (A) Signup and view all the answers

How do you use an abstract class?

You have to inherit it from another class and provide implementations to the abstract methods. (C) Signup and view all the answers

What is the primary purpose of an interface in object-oriented programming?

To define a set of method signatures and their return values (D) Signup and view all the answers

What is the difference between an interface and an abstract class?

An abstract class can have non-abstract methods, while an interface cannot (C) Signup and view all the answers

How do you create an array in Java?

String studentName[] = new String; (A) Signup and view all the answers

What is the difference between creating an array and an ArrayList in Java?

Arrays are static, while ArrayLists are dynamic (C) Signup and view all the answers

How do you add an element to the beginning of an ArrayList in Java?

studentNames.add(0, "John"); (A) Signup and view all the answers

What is the purpose of the `implements` keyword in Java?

To implement an interface (D) Signup and view all the answers

What is the term for the combination of a method name, number and type of parameters?

Method signature (A) Signup and view all the answers

What is the primary difference between an array and an ArrayList in terms of memory allocation?

Arrays are stored on the stack, while ArrayLists are stored on the heap (B) Signup and view all the answers

What is the purpose of an interface in terms of object-oriented programming?

To define a set of method signatures and their return values (A) Signup and view all the answers

How do you print the elements of an ArrayList in Java?

Using a for-each loop (B) Signup and view all the answers

Study Notes

OOP Concepts

Week 5B topics include Abstract Classes, Inheritance, Override, Customization, Interfaces, Contracts in OO, UML, and Collections.

Objects and Abstractions

Abstraction in Java is achieved through Abstract Classes and Interfaces.
Abstraction hides implementation details from the user, who only gets the functionality.

Abstract Class

Definition: An abstract class is a class that is declared abstract and may or may not include abstract methods.
Characteristics:
- Cannot be instantiated.
- Can be subclassed.
- If a class includes abstract methods, the class itself must be declared abstract.
Notes:
- If a class is abstract, it cannot be instantiated.
- When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class.
- If a subclass does not provide implementations, it must also be declared abstract.

Interfaces

Definition: A contract in OO programming that bundles common functionality in classes that are not part of the inheritance hierarchy.
Characteristics:
- Completely "abstract class" that groups related methods with empty bodies.
- Used to provide a set of method signatures.
- Provides return values of methods.
- Tells us how to use an object that implements the interface.
Notes:
- If an abstract class has nothing other than public static final properties and abstract methods, it could be made into an interface.
- All methods in an interface are abstract, so there is no need to declare them as abstract.

Interface Example

A subclass implements an interface using the implements keyword.
Recall: Subclass extends an abstract class.

Collections

Creation:
- Array: String studentName[] = new String[];
- ArrayList: List studentName = new ArrayList<>();
Operations:
- Array: studentName[i++] = “Peter”;
- ArrayList: studentName.add(“Peter”);
Printing:
- Array: `for(int i=0; i

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This quiz covers lecture notes on Object-Oriented Programming (OOP) for CST8132, a Computer Engineering Technology course at Algonquin College.