Detailed explanation of overloading parent class in subclass in object-oriented PHP

This article will give you a detailed explanation of overloading parent classes in PHP object-oriented subclasses. I hope this article will help you understand overloading parent classes in PHP subclasses.

Because functions with the same name cannot exist in PHP, methods with the same name cannot be defined in the same class. The overloading mentioned here means that a method with the same name as the parent class can be defined in a subclass to override the method inherited from the parent class.

Overloading parent class methods in subclasses

The code is as follows

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class Person{
                                                                                                                   public $name;                                                                                                                                                               public function __construct($name="" ){
$this->name =$name;
                                                                                                                  }
             public function say(){
echo "My name is".$this->name ;
           }
                                                                                                      }
?>
class Student extends Person{
                                                                                                               public $name;                                                                                                                                             public function __construct($name=""){
$this->name =$name;
                                                                                                          }
//Here defines a method with the same name as the parent class, overwriting and rewriting the speaking method in the parent class
             public function say(){
echo "My name is ".$this->name ." and I am 25 years old" ;
           }
                                                                                                      }
?>

Overriding methods and access permissions

An overridden method in a subclass cannot use more restrictive access permissions than the overridden method in the parent class.

If the access permission of the method in the parent class is protected, then the permissions of the method to be overridden in the subclass must be protected or public; If the method in the parent class is public, then the permissions of the method to be overridden in the subclass must be It can only be public. Perhaps this is why subclasses can inherit private members of the parent class, but cannot use them.

Number of parameters when rewriting

Subclasses can have a different number of parameters than the parent class. For example, in the following constructor, an additional parameter $age is added.

The code is as follows

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代码如下

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class Student extends Person{

public $name;
public $age;

public function __construct($name="",$age=25){
$this->name =$name;

$this->age =$age;

}

public function say(){

echo "我叫".$this->name ."，今年".$this->age."岁了" ;

}

}
?>

<🎜> class Student extends Person{ <🎜> <🎜> <🎜> public $name; <🎜> public $age; <🎜> public function __construct($name="",$age=25){ <🎜> $this->name =$name; $this->age =$age; } public function say(){ echo "My name is ".$this->name .", and this year ".$this->age." is old"; } ?>

Constructor overriding

The "number of parameters during rewriting" mentioned above has already enabled the subclass to rewrite the constructor of the parent class, but this is not a good way of writing. If you observe carefully, you will find that, The above subclass Student's rewriting of the parent class's Person constructor is actually adding an extra parameter to the parent class's constructor function, but also copying the original parameters of the parent class, because the structure of the parent class Person The function only has one parameter, so we don’t have any trouble writing it down. However, if there is more than one parameter, but several or more, then you will find that it is cumbersome. So is there any way to simplify this problem? Woolen cloth? The answer is yes, you can use "parent::method name" to call the overridden method in the parent class in the overloaded method of the subclass. For example, use "parent::__construct()" to call the overridden constructor method in the parent class. Other methods are similar, so the above code can be simplified to:

The code is as follows

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代码如下

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class Student extends Person{

public $name;

public $age;

public function __construct($name="",$age=25){

parent::__construct($name,$age);

$this->age =$age;
}

public function say(){
parent::say();

echo "，今年".$this->age."岁了" ;

}

}
?>

<🎜> class Student extends Person{ <🎜> <🎜>                                                            <🎜> public $name; <🎜> <🎜> public $age;
                                                                                                                     public function __construct($name="",$age=25){ <🎜> <🎜> parent::__construct($name,$age); <🎜> <🎜> $this->age =$age;
                                                                                              public function say(){
               parent::say(); echo ", this year".$this->age."year old" ;                                                                                                                                                                                                                 }
?>

Let’s look at another example

PHP5 rewriting method
First set up a parent class. This parent class is the "Dog" class. This class describes the characteristics of dog.

Dog has 2 eyes, can run and bark. Just describe it like this.

I have a dog, which is a puppy. It conforms to the characteristics of Dog, but it is different.

My puppy has a name. My puppy is too small. He can’t bark loudly, he can only hum.

We use the concept of inheritance to implement this design.

The code is as follows

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代码如下

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// 狗有两只眼睛,会汪汪叫,会跑.
class Dog {
protected $eyeNumber =2; //属性
//返回封装属性的方法.
public function getEyeNumber(){
return $this->eyeNumber;
}
//狗会叫
public function yaff(){
  return "Dog yaff, wang ..wang ..";
}
//狗会跑
public function run(){
  return "Dog run..running ...";
}
}
$dog = new Dog();
echo "dog have ".$dog->getEyeNumber()." eyes.
";
echo $dog->yaff() ."
".$dog->run();
echo "

";
//这是我的小狗叫"狗狗",它很小.不会汪汪叫,只会哼哼哼..
class MyDog extends Dog {
private $name = "狗狗";
public function getName(){
  return $this->name;
}
    public function yaff(){
  return $this->name." yaff, heng...heng ..";
}
}
$myDog = new MyDog();
echo $myDog->getName()." have ".$myDog->getEyeNumber()." eyes.
";
echo $myDog->yaff() ."
".$myDog->run();
?>

程序运行结果：

dog have 2 eyes.
Dog yaff, wang ..wang ..
Dog run..running ...

狗狗 have 2 eyes.
狗狗 yaff, heng...heng ..
Dog run..running ...

// The dog has two eyes, can bark, and can run.
class Dog {

protected $eyeNumber =2; //Attribute

//Return the method of encapsulating attributes.

public function getEyeNumber(){

代码如下

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// 简化dog类和mydog类,演示重写的访问权限.
class Dog {
protected $eyeNumber =2; //属性
//返回封装属性的方法.
public function getEyeNumber(){
return $this->eyeNumber;
}
}

class MyDog extends Dog {
protected function getEyeNumber(){
return $this->eyeNumber;
}
}
/*
class MyDog extends Dog {
private function getEyeNumber(){
return $this->eyeNumber;
}
}
*/

程序运行结果：
Fatal error: Access level to MyDog::getEyeNumber() must be public (as in class Dog) in E:PHPProjectstest.php on line 15

return $this->eyeNumber; } //Dogs can bark public function yaff(){ return "Dog yaff, wang ..wang .."; } //Dogs can run public function run(){ return "Dog run..running ..."; } } $dog = new Dog(); echo "dog have ".$dog->getEyeNumber()." eyes.
"; echo $dog->yaff() ."
".$dog->run(); echo "

"; //This is my puppy called "Dog". It is very small. It can't bark, it can only hum.. class MyDog extends Dog { private $name = "dog"; public function getName(){ Return $this->name; } Public function yaff(){ return $this->name." yaff, heng...heng .."; } } $myDog = new MyDog(); echo $myDog->getName()." have ".$myDog->getEyeNumber()." eyes.
"; echo $myDog->yaff() ."
".$myDog->run(); ?> Program execution result: dog has 2 eyes. Dog yaff, wang ..wang .. Dog run..running ... The dog has 2 eyes. Dog yaff, heng...heng .. Dog run..running ...

Overriding methods and access permissions An overridden method in a subclass cannot use more restrictive access permissions than the overridden method in the parent class. When the parent class is public and the subclass is private.

The code is as follows

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// Simplify the dog class and mydog class to demonstrate rewritten access rights.<🎜> class Dog {<🎜> protected $eyeNumber =2; //Attribute<🎜> //Return the method of encapsulating attributes.<🎜> public function getEyeNumber(){ <🎜> Return $this->eyeNumber; } } class MyDog extends Dog { protected function getEyeNumber(){ Return $this->eyeNumber; } } /* class MyDog extends Dog { private function getEyeNumber(){ Return $this->eyeNumber; } } */ ?> Program execution result: Fatal error: Access level to MyDog::getEyeNumber() must be public (as in class Dog) in E:PHPProjectstest.php on line 15

When the parent class is public and the subclass is protected.

The code is as follows

代码如下

复制代码

// 简化dog类和mydog类,演示重写的访问权限.
class Dog {
protected $eyeNumber =2; //属性
//返回封装属性的方法.
public function getEyeNumber(){
return $this->eyeNumber;
}
}

class MyDog extends Dog {
private function getEyeNumber(){
return $this->eyeNumber;
}
}

程序运行结果：

Fatal error: Access level to MyDog::getEyeNumber() must be public (as in class Dog) in E:PHPProjectstest.php on line 15

Copy code

代码如下

复制代码

// 简化dog类和mydog类,演示重写方法的参数.
class Dog {
protected $eyeNumber =2; //属性
//返回封装属性的方法.
public function getEyeNumber(){
return $this->eyeNumber;
}
}
class MyDog extends Dog {
//重写的方法与父类的方法有不同的参数数量.
public function getEyeNumber($eys){
$this->eyeNumber = $eys;
return $this->eyeNumber;
}
}

$myDog = new MyDog();
echo "my dog hava ".$myDog->getEyeNumber(3) ." eyes.";
//啸天犬..哈..
//下面这句会报一个丢失参数的错误.
//echo "my dog hava ".$myDog->getEyeNumber() ." eyes.";
?>

程序运行结果：

my dog hava 3 eyes.

// Simplify the dog class and mydog class to demonstrate rewritten access rights.

class Dog {

protected $eyeNumber =2; //Attribute

//Return the method of encapsulating attributes.

public function getEyeNumber(){

return $this->eyeNumber;

}

代码如下

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//2-2 / extends1.php
//构造函数继承的问题.
class Animal{
public $legNum = 0;
public function __construct(){
$this->legNum = 4;
  echo "I am an animal
";
}
}
class Dog1 extends Animal {
public function __construct(){
  $this->legNum = 4;
  echo "I am a Dog .
";
}
}
$dog1 = new Dog1();
echo "
";
echo "legNum is ".$dog1->legNum;
/*
实例化子类时.构造函数被调用了.
*/
?>

程序运行结果：

I am a Dog .
legNum is 4

}

class MyDog extends Dog { private function getEyeNumber(){ return $this->eyeNumber; } } ?> Program execution result: Fatal error: Access level to MyDog::getEyeNumber() must be public (as in class Dog) in E:PHPProjectstest.php on line 15 Number of parameters when rewriting Subclasses can have a different number of parameters than the parent class. (This is different from java, PHP is a weakly typed language.)

The code is as follows

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// Simplify the dog class and mydog class and demonstrate the parameters of the overridden method.<🎜> class Dog {<🎜> protected $eyeNumber =2; //Attribute<🎜> //Return the method of encapsulating attributes.<🎜> public function getEyeNumber(){ <🎜> return $this->eyeNumber; } } class MyDog extends Dog { //The overridden method has a different number of parameters than the parent class method. public function getEyeNumber($eys){ $this->eyeNumber = $eys; return $this->eyeNumber; } } $myDog = new MyDog(); echo "my dog hava ".$myDog->getEyeNumber(3) ." eyes."; //Howling Sky Dog...ha... //The following sentence will report a missing parameter error. //echo "my dog hava ".$myDog->getEyeNumber() ." eyes."; ?> Program execution result: my dog hava 3 eyes. Constructor overriding In the following example, both the parent class and the subclass have their own constructors. When the subclass is instantiated, the constructor of the subclass is called, but the constructor of the parent class is not called. Please compare the first Section constructor inheritance.

The code is as follows

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//2-2 / extends1.php<🎜> //Problems with constructor inheritance.<🎜> class Animal{<🎜> public $legNum = 0; <🎜> public function __construct(){<🎜> $this->legNum = 4; echo "I am an animal
"; } } class Dog1 extends Animal { public function __construct(){ $this->legNum = 4; echo "I am a Dog .
"; } } $dog1 = new Dog1(); echo "
"; echo "legNum is ".$dog1->legNum; /* When instantiating a subclass, the constructor is called. */ ?> Program execution result: I am a Dog . legNum is 4 Note: This is different from Java. In Java, constructors cannot be inherited, and when a subclass is instantiated, the constructor of the subclass is called, and the constructor of the parent class is also called.

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