Classes and stuff?

Question 1

What are three modifiers for accessing privileges?

Answer 1

Public,
Private,
Protected

Question 2

What are the 2 ways to create objects?

Answer 2

Copy and adjust existing ones.

Instantiate a template

Question 3

What way does Java create objects?

Answer 3

By instantiating a template

Question 4

What is a class used for in Object-Orientated Programming?

Answer 4

A class is a template for buliding objects

Question 5

What three things does a class have when being used in Object-Orientated Programming?

Answer 5

Attributes
Constructors
Methods

Question 6

How do you create a new object in Java?

Answer 6

ObjectType name = new ObjectConstructor(args);

Question 7

If an object bob has a private attribute age, can this attribute be accessed using bob.age;?

Answer 7

No, you need to use a getter method inside the class

Question 8

If an object bob has a public attribute age, can this be accessed using bob.age;?

Answer 8

Yes, but this is bad practice to do, attributes should be private or protected

Question 9

What is the difference between private and protected?

Answer 9

Private can only be used by that class, protected acts like private from a user’s perspective but can be used by subclasses

Question 10

What 2 things happen when you instantiate an object with the keyword new?

Answer 10

The JVM allocates memory to store the new object.

A constructor method is called to initialise it.

Question 11

What is the syntax for creating a constructor for a class called XClass?

Answer 11

public XClass(parameters) {
    //attribute assingments
}

Question 12

How do you call one constructor from within another?

Answer 12

You use the keyword ‘this’.

Question 13

What does the keyword static do?

Answer 13

This means the variable belongs to the class rather than the instance and thus is the same for all objects of this class.
Static methods can only access static variables.

Question 14

What are some of the advantages of using inheritance in OOP?

Answer 14

• Introduces more abstraction
• Enhances code re-usability
• Improves code readability
• Can reduce software maintenance costs
• Allows multiple people to program subclasses simultaneously

Question 15

How does inheritance work in OOP?

Answer 15

Subclasses inherit methods and attributes from the superclass and extend them (for instance to add more specific things)

Question 16

How is a class declared as a subclass of a superclass?

Answer 16

modifiers class SubClass extends SuperClass {
//class body}

Question 17

Can you call a superclass constructor from within the subclass?

Answer 17

Yes, you use the keyword ‘super’. It must be the first thing in the constructor method.

Question 18

What is overwriting/overriding?

Answer 18

When you redeclare a method from the superclass in the subclass. The version in the subclass is the version that will be used.

Question 19

What types of methods/attributes will a subclass inherit (private/public/protected)?

Answer 19

Subclasses will only inherit public and protected attributes and methods.
Anything private are not inherited

Question 20

What is an abstract class?

Answer 20

An abstract class is a class which can be extended to a subclass but not instantiated by itself.

Question 21

How do you declare an abstract class?

Answer 21

public abstract class ClassName {
//class body}

Question 22

What is the naming convention for interfaces?

Answer 22

____able

Question 23

Do abstract methods have the method body written when declared?

Answer 23

No, the method body is created when the subclass overrides the method (which it must do for abstract methods)

Question 24

What does an interface contain?

Answer 24

Method signatures.
The bodies are written in clases implementing the interfaces.

They can also contain attributes for constants.

Question 25

How would interfaces be used in instantiation?

Answer 25

``` Interface name = new Constructor(); The interface is put as a type for the object and the object is created with its usual constructor. ```

Question 26

How does a class use an interface?

Answer 26

``` public class ClassName implements InterfaceName1, InterfaceName2, etc { //Class Body} ```

Question 27

How many interfaces can one class implement?

Answer 27

As many as it wants to

Question 28

If a class implements an interface what must that class contain?

Answer 28

The method bodies for methods declared in the interface.