OOP Basics II

Question 1

What is a constructor?

Answer 1

A method named __construct(), which is called on each newly-created object.

Question 2

If the child class defines a constructor, the parent constructor is…

Answer 2

…not called.

Question 3

How do you run a parent constructor?

Answer 3

Call parent::__construct() within the child constructor.

Question 4

When is a destructor called?

Answer 4

As soon as there are no other references to a particular object.

Question 5

How do you call a parent destructor?

Answer 5

Call parent::__destruct() in the destructor body.

Question 6

Is a destructor called if script execution is stopped using exit()?

Answer 6

Yes.

Question 7

If a method is declared without an explicit visibility keyword, what is its visibility?

Answer 7

Public.

Question 8

Can objects of the same type access each other’s private and protected members, even though they are not the same instances?

Answer 8

Yes.

Question 9

What is the scope resolution operator?

Answer 9

::

Allows access to static, constant, and overridden properties or methods of a class.

Question 10

What does the ‘static’ keyword do?

Answer 10

Declaring class properties or methods as ‘static’ makes them accessible without needing an instantiation of the class.

Question 11

Can a property declared as static be accessed with an instantiated class object?

Answer 11

No.

Question 12

Can a static method be accessed with an instantiated class object?

Answer 12

Yes.

Question 13

Can classes defined as ‘abstract’ be instantiated?

Answer 13

No.

Question 14

Any class that contains at least one abstract method must also be…

Answer 14

…abstract.

Question 15

When inheriting from an abstract class, all methods marked abstract in the parent class must be…

Answer 15

…defined by the child.

Question 16

What type of visibility do methods inherited from an abstract class need to have?

Answer 16

The same or a less restricted visibility.

Question 17

Does a method that inherits from an abstract class have to have the same number of arguments?

Answer 17

Yes.

Question 18

What is an object interface?

Answer 18

Interfaces specify which methods a class must implement, without having to define these methods.

Question 19

What is the required visibility for methods declared in an interface?

Answer 19

Public.

Question 20

How do you implement an interface?

Answer 20

With the ‘implements’ keyword.

Question 21

How do you implement more than one interface?

Answer 21

By separating each interface name with a comma.

Question 22

A class implementing an interface must use the exact same ____ ____ as are defined in the interface.

Answer 22

Method signatures.

Question 23

How are interface constants different from class constants?

Answer 23

Interface constants cannot be overridden by a class/interface that inherits them.