Detailed explanation of the Final keyword in object-oriented PHP (code example)

Objectives of this article:

1. Understand the definition of the Final keyword in PHP

2. Understand the role of the Final keyword in PHP

3. Understand the Final keyword in PHP Keyword usage scenarios

4. Master the specific implementation of the Final keyword in PHP

Still following the previous consistent thinking, we will learn through the 3W1H method, so first let’s understand it

(1) Understand the definition of the Final keyword in PHP (What)

If you add final before a class, then this class cannot be inherited. If you add final before a method, Then this method cannot be overridden

(2) Understand the role of the Final keyword in PHP (Why)

The main functions are 2 points:

1. Prevent Classes are inherited

2. Prevent class methods from being overridden

(3) Understand the usage scenarios of the Final keyword in PHP (Where)

If you want a class If there is no subclass, or the method of a class cannot be overridden, then you can consider using final implementation

(4) Master the specific implementation of the Final keyword in PHP (How)

Summary:

1. The definition format of the final class is: final class class name {}

2. Pay special attention to the fact that only PHP5 has the concept of final keyword. This concept did not exist before PHP5

3. The definition format of the final method is: final public (or protected) function method name (parameters...){}

4. Once a class is defined as a final class, it cannot Inherited, that is, it cannot have subclasses

5. Once a method is defined as a final method, it cannot be overridden by a subclass

All the summaries are based on practice. So next, we still have to prove it one by one, so that we can use

with confidence (5), specific code

1, case one:

Practical goals:

1. The definition format of the final class is: final class class name {}

<?php
//定义“人”类
final class Human{
    public function eat(){
        echo "Human 中的eat方法被执行了<br/>";
    }
}

$human = new Human();
$human->eat();
?>

The operation result is:

The eat method in Human is Executed

2. Case 2:

Practical goal:

1. The definition format of the final method is: final public (or protected) function Method name (parameters...){}

<?php
class Human{
    final public function eat(){
        echo "Human 中的 类型为final的eat方法被执行了<br/>";
    }
}
$human = new Human();
$human->eat();
?>

The operation result is:

The final eat method in Human is executed

3. Case 3:

Practical goals:

1. Once a class is defined as a final class, it cannot be inherited, that is, it cannot have subclasses

<?php
//定义“人”类
final class Human{
    public function eat(){
        echo "Human 中的 类型为final的eat方法被执行了<br/>";
    }
}

//定义Nba球员类
class NbaPlayer extends Human{
    public function eat(){
        
    }
}
?>

The running result is:

Fatal error: Class NbaPlayer may not inherit from final class (Human) in D:\E-class\class-code\classing\index.php on line 14

4. Case 4:

Practical goal:

1. Once a method is defined as a final method, it cannot be overridden by a subclass

<?php
//定义“人”类
class Human{
    final public function eat(){
        echo "Human 中的 类型为final的eat方法被执行了<br/>";
    }
}

//定义Nba球员类
class NbaPlayer extends Human{
    public function eat(){
        echo "NbaPlayer中的eat方法，重写了父类的eat方法<br/>";
    }
}
?>

The running result is:

Fatal error: Cannot override final method Human::eat() in D:\E-class\class-code\classing\index.php on line 14

(6) Apply what you have learned

So far, we should have a clear understanding of final. Next, apply what we have learned and use the knowledge we have learned to solve the following problems Question

Question: Based on years of experience, many data operation methods can actually be reused. In addition to being used in one project, they can be used in many projects, and they can be used in many places in a project. Reuse, so I plan to encapsulate these common methods into a class, but this class does not need to have subclasses, and I don’t want the methods inside to be overridden. What should I do?

Idea analysis:

1. Create a class that contains common data operation methods

2. Because you don’t want the class to be Inheritance, so combined with the role of final, we can define the class as a final class

3. Once a class is defined as a final class, the methods inside will naturally not be overridden, because there are no subclasses. How can we rewrite it in a subclass?

The specific code is as follows:

<?php
final class MyDataOpClass{
    public function abs(){
        //求绝对值
    }
    //产生随机数
    public function rand(){
        echo "产生随机数方法";
    }
    //获取数组中的最大值
    public function getMax($numArr){
        
    }
    //获取数组中的最小值
    public function getMin($numArr){

    }
    //其他方法就此省略
}
$mymath = new MyDataOpClass();
$mymath->rand();
?>

The running results are as follows:

Generate random number method

Explanation: This example is a bit simple, but I hope everyone will pay attention to their own analysis of ideas and be as accurate and clear as possible

Summary:

1. The main content of this article Explained the definition and function of final as well as the specific implementation

I hope this article can bring you some help, thank you all! ! !

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