"Essential knowledge points for PHP object-oriented programming: in-depth understanding of objects and classes"

php editor Yuzai will take you to deeply explore the essential knowledge points of PHP object-oriented programming: objects and classes. In object-oriented programming, objects are instantiations of classes, and classes are templates for objects. A deep understanding of the relationship between objects and classes is crucial to mastering PHP object-oriented programming. This article will introduce in detail the concepts, properties, methods of objects and classes and how to create and use them. Let's explore the mysteries of objects and classes together and improve PHP programming skills!

Properties are variables of objects, they store the state of the object. Methods are functions of an object and they define the behavior of the object. A constructor is a special method of a class that is automatically called when an object is created.

2. Instantiate objects

Instancing an object refers to the process of creating an object using a class. When instantiating an object, php creates a new object and sets the object's properties to the initial values ​​defined in the class.

3. Properties

Properties are variables of objects, they store the state of the object. Properties can be public, private, or protected. Public properties can be accessed anywhere in the class, private properties can only be accessed within the class itself, and protected properties can only be accessed within the class itself and its subclasses.

4. Method

Methods are functions of an object, they define the behavior of the object. Methods can be public, private, or protected. Public methods can be called anywhere in the class, private methods can only be called within the class itself, and protected methods can only be called within the class itself and its subclasses.

5. Inheritance

Inheritance is an important concept in OOP. It allows a class to inherit properties and methods from another class. Derived classes can override methods inherited from the base class to provide different implementations.

6. Combination

Composition is another important concept in OOP. It allows a class to use the functionality of other classes by creating instances of other classes. Composition differs from inheritance in that composition does not involve creating new classes.

7. Object-oriented design (OOP) principles

OOP principles are a set of principles that guide developers on how to write code that is more flexible and easier to maintain. These principles include encapsulation, abstraction, inheritance, and polymorphism.

Encapsulation refers to encapsulating the state and behavior of an object so that they can only be accessed through the object's methods.

Abstraction refers to hiding the implementation details of an object and only exposing the public interface of the object.

Inheritance refers to allowing a class to inherit properties and methods from another class.

Polymorphism refers to allowing an object to respond to the same call in different ways.

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