Methods and property visibility in PHP

It is possible to have three types of visibility of PHP properties or methods in classes. These are public, protected and private. 

The difference between these three as follow:

Public properties and methods are accessible by anyone.

Protected are accessible by this class and classes that extends it.

Private properties are accessible by this class only.

YouTube video

FAQs

What are the three visibility types for properties and methods in PHP classes?

The three visibility types in PHP for class properties and methods are public, protected, and private.

How does public visibility affect access?

Properties and methods marked as public are accessible from anywhere, both inside and outside the class where they are defined, and also in any classes that extend the original class.

What is the scope of protected visibility?

Protected properties and methods are accessible within the class where they are defined and within any classes that inherit from or extend that class. They are not accessible from outside this class hierarchy.

Where can private properties and methods be accessed?

Private properties and methods have the most restricted access. They can only be accessed within the specific class in which they are declared. They are not accessible from subclasses or from outside the class.

Can a property or method be accessed from a subclass if it's marked as private?

No, private properties and methods are not accessible from subclasses. Their scope is limited to the class in which they are defined.

Is there any difference in how visibility types apply to properties versus methods?

No, the rules for public, protected, and private visibility apply equally to both properties (variables) and methods (functions) within a PHP class.

If a class B extends class A, can methods in class B access protected members of class A?

Yes, if a class B extends class A, then methods within class B can access the protected properties and methods of class A.

Which visibility type provides the most limited access?

The private visibility type provides the most limited access, restricting access to only the class where the property or method is declared.

PHP Visibility Types: Study Guide

Quiz

How can you access a public property of a class?

Where can a protected method of a class be called from?

Can a child class access a private property of its parent class? Explain why or why not.

If a class has a public method, can a separate, unrelated function call this method?

What is the scope of accessibility for a private property?

Can a method declared as protected in a parent class be accessed directly by an instance of the parent class?

If a child class inherits from a parent class, can the child class access protected members of the parent?

Is there any restriction on who can access a public member of a class?

Describe the difference in accessibility between protected and private visibility.

Within a class definition, can a method defined in that class access a private property also defined in that class?

Quiz Answer Key

Public properties are accessible by anyone. This means you can access them directly from outside the class using the object instance.

A protected method can be called from within the class where it is defined, and also from within any class that extends it.

No, a child class cannot access a private property of its parent class. Private members are only accessible within the class where they are defined.

Yes, if a class has a public method, a separate, unrelated function can call this method. Public members are accessible by anyone.

The scope of accessibility for a private property is limited to the class itself where the property is defined.

No, a method declared as protected in a parent class cannot be accessed directly by an instance of the parent class from outside. It is only accessible within the class or its descendants.

Yes, if a child class inherits from a parent class, the child class can access protected members of the parent. This is the definition of protected visibility.

No, there is no restriction on who can access a public member of a class. They are designed to be accessible by anyone.

Protected members are accessible by the class itself and its extending classes, while private members are only accessible by the class itself where they are defined.

Yes, within a class definition, a method defined in that class can access a private property also defined in that class. This is the intended use of private members.

Essay Questions

Discuss the purpose of visibility types in object-oriented programming, specifically in the context of PHP. How do they contribute to code organization and maintainability?

Explain the practical scenarios where using public, protected, and private visibility would be most appropriate. Provide examples for each type.

Analyze the implications of using private visibility on inheritance. How does it affect the ability of child classes to interact with the parent class's internal state?

Compare and contrast the benefits and drawbacks of using protected visibility versus public visibility. When might you choose one over the other?

Describe how visibility types enforce encapsulation in PHP classes. What are the advantages of achieving a strong level of encapsulation?

Glossary

Public: A visibility type in PHP that allows properties and methods to be accessed from anywhere, both inside and outside the class.

Protected: A visibility type in PHP that allows properties and methods to be accessed from within the class itself and by any classes that extend it.

Private: A visibility type in PHP that restricts access to properties and methods to only within the class where they are defined.

Properties: Variables declared within a class that represent the data or state of an object.

Methods: Functions declared within a class that define the behavior or actions an object can perform.

Class: A blueprint for creating objects, defining their properties and methods.

Extends: The keyword used in PHP to indicate that one class inherits from another, creating a child class that inherits the properties and methods of the parent class.