Detailed explanation of PHP object-oriented abstract classes (code examples)

Objectives of this article:

1. Understand the definition of abstract classes in PHP

2. Understand the role of abstract classes in PHP

3. Understand the functions of abstract classes in PHP Usage scenarios

4. Master the specific implementation of abstract classes 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 abstract classes in PHP (What)

Abstract classes are often used to characterize the analysis and design of problem areas. Abstract Concept is an Abstract for a series of specific concepts that look different but are essentially the same. Classes usually modified with abstract in programming statements are Abstract classes.

#The difference between the interface and the interface is that the methods in the interface are not implemented, but are simply defined, but the methods in the abstract class can be implemented of.

(2) Understand the role of abstract classes in PHP (Why)

Among the classes in PHP, many classes will be constantly rewritten. This Sometimes we can use abstract classes, how to do it? That is to write a public class first, and then we can call it repeatedly after instantiating it. This can improve the reusability of the code

(3) Understand the usage scenarios of abstract classes in PHP (Where)

1. If you find that many classes in the code are similar or Common methods, we can extract these same or similar methods and encapsulate them into abstract classes.

Abstract classes and interfaces are somewhat similar. It can be said that the interface is a special abstract class, but the interface is full of abstract methods (the so-called abstract means that there is no specific implementation), but in the abstract class Some methods can have implemented functions,

(4) Master the specific implementation of abstract classes in PHP (How)

Summary:

1. Abstract classes The definition is defined through abstract, such as abstract class class name {}

2. The definition of the method of the abstract class is also defined through abstract, such as abstract public function method name (){}

3. Abstract Classes cannot be instantiated

4. To inherit an abstract class, use the keyword extends

5. Subclasses of abstract classes must implement things that are not implemented in the abstract class. All methods, that is to say, rewrite all abstract methods in the abstract class

6. Although the subclasses of the abstract class do not implement the methods that have been implemented in the abstract class, they can still call these methods. In fact, combined with inheritance We can understand this very well

Every summary is obtained through practice. Now we use practice to demonstrate the summary, which can promote understanding and make each summary more understandable. Clear and intuitive

(5), specific code

Case 1,

Practice goals:

1. The definition of an abstract class is defined by abstract, such as abstract class class name {}

2. The definition of an abstract class method is also defined by abstract, such as abstract public function method name (){}

The specific code is as follows:

<?php
abstract class Animal{
    abstract public function eat();//抽象方法
    //呼吸
    public function breath(){
        //所有动物的呼吸方法都是一样的，就不需要使用多态了
        echo "呼吸<br/>";
    }
}
?>

Case 2,

Practical goals:

1. Abstract classes cannot be instantiated The specific code of

is as follows:

<?php
abstract class Animal{
    abstract public function eat();//抽象方法
    //呼吸
    public function breath(){
        //所有动物的呼吸方法都是一样的，就不需要使用多态了
        echo "呼吸<br/>";
    }
}
$animal = new Animal();
?>

The running result is:

Fatal error: Uncaught Error: Cannot instantiate abstract class Animal in D:\E-class\class-code\classing\index.php:10 Stack trace: #0 {main} thrown in D:\E-class\class-code\classing\index.php on line 10

案例四、

实践目标：

1、要继承一个抽象类，通过关键字extends

2、抽象类的子类必须要实现抽象类中未实现的所有方法，也就是说要重写抽象类中所有abstract的方法

具体代码如下：

<?php
abstract class Animal{
    abstract public function eat();//抽象方法
    //呼吸
    public function breath(){
        //所有动物的呼吸方法都是一样的，就不需要使用多态了
        echo "呼吸<br/>";
    }
}
//定义猴子
class Monkey extends Animal{
    
}
?>

如果Monkey类继承了抽象类，但不实现里面的abstract方法，那么运行结果为：

Fatal error: Class Monkey contains 1 abstract method and must therefore be declared abstract or implement the remaining methods (Animal::eat) in D:\E-class\class-code\classing\index.php on line 13

接下来我们来实现abstract方法

具体代码如下：

<?php
abstract class Animal{
    abstract public function eat();//抽象方法
    //呼吸
    public function breath(){
        //所有动物的呼吸方法都是一样的，就不需要使用多态了
        echo "呼吸<br/>";
    }
}
//定义猴子
class Monkey extends Animal{
    //实现抽象类中的抽象方法
    public function eat(){
        echo "我是猴子类中的eat方法<br/>";
    }
}
$monkey = new Monkey();
$monkey->eat();

?>

运行结果如下：

我是猴子类中的eat方法

案例五、

实践目标：

1、抽象类的子类虽然没有实现抽象类中的已经实现的方法，一样可以调用这些方法，其实结合继承我们可以很好理解这点

具体代码如下：

<?php
abstract class Animal{
    abstract public function eat();//抽象方法
    //呼吸
    public function breath(){
        //所有动物的呼吸方法都是一样的，就不需要使用多态了
        echo "抽象类中的呼吸方法<br/>";
    }
}
//定义猴子
class Monkey extends Animal{
    //实现抽象类中的抽象方法
    public function eat(){
        echo "我是猴子类中的eat<br/>";
    }
}
$monkey = new Monkey();
$monkey->eat();
$monkey->breath();
?>

运行结果如下：

我是猴子类中的eat
抽象类中的呼吸方法

（六）、学以致用

问题：将以下真实场景，用抽象类还原出来

小芳放学回到家中，一进家门，只见心爱的小狗“小爱”马上就对主人摇起了尾巴，小芳笑了笑，走过去，抱起了小狗，最后，小芳和小狗亲了一口

思路分析：

1、对象分析：学生，小狗

2、对象属性分析：结合（现实世界+具体场景）

    学生：名称

    狗：名称

3、对象方法分析：结合（现实世界+具体场景）

    学生：

        （1）、放学 

        （2）、回到家中

        （3）、走路

        （4）、看

        （5）、笑

        （6）、抱东西

        （7）、亲嘴

       狗：

        （1）、看

        （2）、摇尾巴

        （3）、亲嘴

4、我们发现这2个对象都有相似的方法，看，亲嘴，所以我们可以把它们封装到抽象类中，并且这2个方法不需要子类去重写，因为都是一样的

具体代码如下：

<?php
abstract class Animal{
    //看
    public function look($obj){
        //所有动物的呼吸方法都是一样的，就不需要使用多态了
        echo "看见了".$obj->name."<br/>";
    }
    //亲嘴
    public function kiss($fromobj,$toobj){
        echo $fromobj->name."亲了".$toobj->name."一口<br/>";
    }
    
}
//学生
class Student extends Animal{
   public $name = "";
   public function __construct( $name ){
       $this->name = $name;
   }
    // 1、放学
   public function offschool(){
       echo $this->name."放学了<br/>";
   }
   //回家
   public function goHome(){
    echo $this->name."回到家中<br/>";
   }
    // 2、走路
    public function walk(){
        echo $this->name."走了过去<br/>";
    }
    // 3、看

    // 4、笑
    public function smile(){
        echo $this->name."微笑了<br/>";
    }
    // 5、抱东西
    public function hug($obj){
        echo $this->name."抱起了".$obj->name."<br/>";
    }
    // 6、亲嘴
   
}
//狗
class Dog extends Animal{
   public $name = "";
   public function __construct( $name ){
       $this->name = $name;
   }
    //1、看

    //2、摇尾巴
    public function wagTail(){
        echo $this->name."摇了尾巴<br/>";
    }

    //3、亲嘴
}
//创建对象
$xf = new Student("小芳");
$dog = new Dog("小爱");
//小芳放学了
$xf->offschool();
//小芳放学回到家中，一进家门，只见心爱的小狗“小爱”马上就对主人摇起了尾巴，小芳笑了笑，走过去，
//抱起了小狗，最后，小芳和小狗亲了一口
//小芳回答家中
$xf->goHome();
//小芳看见小狗
$xf->look($dog);
//小狗摇尾巴
$dog->wagTail();
//小芳笑了笑
$xf->smile();
//小芳走过去
$xf->walk();
//抱起小狗
$xf->hug($dog);
//小芳亲了小狗
$xf->kiss($xf,$dog);
//小狗也亲了小芳
$dog->kiss($dog,$xf);
?>

运行结果为：

Xiaofang is after school
Xiaofang returns home
I see Xiao Ai
小Ai wagged her tail
Xiaofang smiled
Xiaofang walked over
Xiaofang hugged Xiaoai
Xiao Fang kissed Xiao Ai
Xiao Ai kissed Xiao Fang

(7), Summary

1. This article mainly explains the definition, function and specific implementation of abstract classes in PHP

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

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