How to use parent:: in php?

In PHP, you cannot define functions with the same name, including methods with the same name in the same class, so there is no method overloading. Methods with the same name as those of the parent class can be defined in the subclass alone, because the methods of the parent class already exist in the subclass, so the methods inherited from the parent class can be overridden in the subclass.

The method of overriding the parent class in a subclass is to overwrite the methods inherited from the parent class in the subclass. Can’t the methods in the parent class be used directly if they are inherited by the subclass? Why do we need to overload it? Because there are some situations that we have to cover. For example, there is a "Bird" class, in which the general method "Fly" for birds is defined. Taking the "ostrich" class as its subclass will inherit the "flying" method, but as soon as the "flying" method in the "ostrich" class is called, the ostrich will fly away. Although ostriches cannot fly, other characteristics have the characteristics of "birds". Therefore, when declaring the "ostrich" class, you can still inherit the "bird" class, but you must add the "bird" class to the "ostrich" class. To rewrite the "flying" method inherited from the subclass, you need to overload the method in the parent class in the subclass.

In the following example, there is a "speak" method in the declared Person class. The Student class can directly use the "speak" method after inheriting the Person class. However, the "speak" method in the Person class can only speak its own membersproperties, while the Student class extends the Person class and adds several new member properties. The code is as follows:

<?php
class Person{
protected $name;
protected $sex;
protected $Wage;
function construct($name="",$sex="男",$age=1){
$this ->name = $name;
$this ->sex = $sex;
$this ->age = $age;
}
//在人类中声明一个通用的说话方法，介绍一下自己
function say(){
echo "我的名字：".$this-> name."，性别：".$this ->sex."，年龄：".$this ->age."。<br>"；
}
}
//声明一个学生类，使用extends关键字扩展（继承）person类
class Student extends Person {
private $school; //在学生类中声明一个所在学校school的成员属性
//覆盖父类中的构造方法，在参数列表中添加一个学校属性，用来创建对象并初始化成员属性
function construct($name="",$sex="男",$age=1,$school=""){
$this ->name = $name;
$this ->sex = $sex;
$this ->age = $age;
$this ->school = $school;
}
function study(){
echo $this ->name."正在".$this ->school."学习<br>";
}
//定义一个和父类中同名的方法，将父类中的说话方法覆盖并重写，多说出所在的学校名称
function say(){
echo "我的名字：".$this ->name."，性别：".$this ->sex."，年龄：".$this ->age."，在".$this ->school."学校上学<br>";
}
}
$student= new Student("张三","男",20,"edu"); //创建一个学生对象，并传给一个学校名称参数
$student -> say(); //调用学生类中覆盖父类的说话方法
?>

The output result after running the modified program is:

My name is: Zhang San, gender: male, my age is: 20. Studying in edu school

In PHP, it provides the function of calling the overridden method of the parent class in the overloaded method of the subclass. In this way, in the method overridden by the subclass, you can continue to use the methods inherited from the parent class and overridden, and then add some new functions as required. The format of the call is to use "parent: method name" to call the overridden method in the parent class in the overloaded method of the subclass. Modify the code in the above example, use "parent::construct()" in the overridden constructor of the subclass to call the overridden constructor of the parent class, and add an additional member attribute for the newly extended member of the subclass. Initialization code. Use "parent::say()" in the say() method overridden in the subclass to call the overridden say() method in the parent class, and then add the function of outputting the member attributes of the subclass.

The code is as follows:

<?php
class Person{
protected $name;
protected $sex;
protected $Wage;
function construct($name="",$sex="男",$age=1){
$this ->name = $name;
$this ->sex = $sex;
$this ->age = $age;
}
//在人类中声明一个通用的说话方法，介绍一下自己
function say(){
echo "我的名字：".$this-> name."，性别：".$this ->sex."，年龄：".$this ->age."。<br>"；
}
}
//声明一个学生类，使用extends关键字扩展（继承）person类
class Student extends Person {
private $school; //在学生类中声明一个所在学校school的成员属性
//覆盖父类中的构造方法，在参数列表中添加一个学校属性，用来创建对象并初始化成员属性
function construct($name="",$sex="男",$age=1,$school=""){
//调用父类中被覆盖的构造方法，为从父类中集成过来额出行赋初值
parent::construct($name,$sex,$age);
$this ->school = $school;
}
function study(){
echo $this ->name."正在".$this ->school."学习<br>";
}
//定义一个和父类中同名的方法，将父类中的说话方法覆盖并重写，多说出所在的学校名称
function say(){
parent::say(); //调用父类中被本方法覆盖掉的方法
echo "在".$this ->school."学校上学<br>";
}
}
$student= new Student("张三","男",20,"edu"); //创建一个学生对象，并传给一个学校名称参数
$student -> say(); //调用学生类中覆盖父类的说话方法
?>

The output result of the above example is the same as the previous example, but in this case it is overwritten by directly calling the parent class in the subclass The method is much simpler. In addition, when a subclass overrides a method of a parent class, it must be noted that the access permissions of the methods overridden in the subclass must not be lower than the access permissions of the overridden methods of the parent class. For example, if the access permission in the parent class is protected, then the permission of the method overridden in the child class must be protected or public.

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