Let you understand the class definition class and member attribute methods in PHP

In the previous article, I brought you "Do you know the custom error handling function and error shielding in PHP?", which brought you the details of PHP error handling. Knowledge, in this article we will take a look at the relevant knowledge of object-oriented in PHP. I hope it will be helpful to everyone!

Object-oriented actually abstracts the problem that needs to be dealt with as an object, and then solves the actual problem of the object through the properties and behavior of the object. Then let's take a look at how to define classes and objects in PHP.

class definition class

In PHP, this class is an abstract concept. We can understand that everything in the world has its own attributes and methods. Attributes refer to the nature of a thing, such as a basketball. Its attributes refer to its size, color, weight, etc.; its methods That is the function he has.

In short, a class is a collection of variables (class attributes) and functions (class methods) that act on these variables. Attributes and methods are the basis of a class.

In PHP we can define a class by adding the class keyword and the class name. Its syntax format is as follows:

Naming rules and variables for class names The naming rules for names and function names are very similar, and they all follow the custom naming rules in PHP.

• The class name should start with a letter and or underscore and consist of letters, numbers and underscores.

• When the class name consists of multiple words, it is generally customary to capitalize the first letter of each word.

• You need to pay attention to The important thing is that the class name should have a certain meaning and should not be composed of just a few letters.

In the above syntax format, the keywords that modify the class can be omitted. Abstract and final are usually used as keywords to modify the class.

Member attributes

After understanding the grammatical format of the class, we should understand the member attributes of the class. What are member attributes? Variables declared directly in a class become member attributes, also called member variables. Multiple variables can be declared in a class, that is, there are multiple member attributes in the class, and each variable stores different attribute information of the class. Its syntax format is as follows:

What we need to pay attention to is that when declaring member attributes in a class, it must be modified with a keyword in front. This is different from when declaring variables. In the class Declaring variables must be modified with keywords. Some of the keywords are meaningful. If you do not need to modify them with other meanings, you must use the "var" keyword to modify them. It has no specific meaning, but if you have other specific meanings, you must use other keywords. Words to modify.

Next, I will list some commonly used modification keywords:

• public: Use it to modify the declared member attributes in the class. Internal, sub-part and external can be used without restriction, indicating that it is a public one.
  

• protectrd: The member attributes declared after being modified with it can be used inside the class and subparts, but cannot be used outside the class.

• pirvate: The member attributes declared after being modified with it can only be used inside the class, and cannot be used in subparts or outside the class.

The example is as follows:

Define a class named Family, and use different keywords to modify member attributes in the class.

Member method

Member method is a function defined in the class. The function implements an independent function and is related to The difference between functions is that member methods implement a behavior of the class and are part of the class. Multiple member methods can be declared in a class. When declaring member methods, it should be noted that the access permission modifier can be added in front of the function keyword to control access permissions.

Examples are as follows:

In PHP, there are also type declarations,

Introduced type declarations, we can provide member methods The formal parameter and return value declaration type, the format is as follows:

The parameter type can include integer, string, floating point and Boolean, examples are as follows:

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