PHP class method rewriting principles

Maybe we rarely use this knowledge point in our daily work, but I still like to find out the knowledge points that I encounter but are not clear about

PHPClass method rewriting rules

1, finalModification Class methods cannot be overridden by subclasses

Final modified class methods cannot be overridden by subclasses Even if the final private method cannot be inherited, subclasses still cannot align and rewrite

class FinalMethod
{
    //可继承不可重写
    final public function finalPublic()
    {
        echo "can be inherited, but be overrided";
    }
    //可继承不可重写
    final protected function finalProtected()
    {
        echo "can be inherited, but be overrided";
    }
    //不可继承不可重写 虽然子类继承不到父类的private方法 但同时也会被final限制无法重写
    final private function finalPrivate()
    {
        echo "can not be inherited or be overrided";
    }
    //虽然不可继承 但子类里可重写此方法
    private function private()
    {
        echo "can not be inherited ,but be overrided";
    }
}
 
class Override extends FinalMethod
{
    //error
    public function finalPublic()
    { 
    }
    //error
    protected function finalProtected()
    {
    }
    //error
    private function finalPrivate()
    {
    }
    //correct
    public/protected/private function private()
    {
        //子类继承父类重写父类方法时访问级别只能更加宽松 不可更为严格
    }
}

2. Whether PHP overrides parent class methods only It will be judged based on whether the method names are consistent (after 5.3, the number of parameters of the parent class method must be consistent when rewriting it)

This does not mean that method parameters have no effect. PHP does not have an

overloading mechanism, so whether it is rewritten will only be judged by the method name. (C/C++ is considered an override only when the method names are the same and the parameters are also the same. Otherwise, it is overloaded, that is, a polymorphic function state is newly defined.) When the method names are the same, they are considered to be in Rewrite the parent class method. Parameters can be different in 5.2. After 5.3, the parameters must be consistent with the parent class method, and all follow the rules of inherited access levels.

class Father
{
    public function index($args_1)
    {
    }
}
 
class Child extends Father
{
    //5.3以后重写方法必须与父类保持参数个数相同
    public function index($args_1, $args_2)
    {
        //在C/C++中此为重载非重写，因为C/C++具有标准的多态机制，会因参数不同而视为某一方法的另一种态
        //but在php中此依然为重写 但5.3以后此为非法 必须与父类的方法参数个数保持一致
    }
    //5.3以后重写方法必须与父类保持参数个数相同
    private function index($args_1, $args_2)
    {
        //C/C++会因为参数不同于父类方法而视为重载，即新定义了一个函数的态，所以不会受到继承访问权限的限制
        //但php仍然会被视为对父类方法的重写，会受到继承访问权限的升降规则限制
    }
}

3. When overriding, the access level can only be equal to or looser than that of the parent class. The access level cannot be increased.

The public method of the parent class cannot be rewritten as protected or private by the subclass. The protected method cannot be rewritten as private and can be relaxed. er, it cannot be strictly er

class Father
{
    public function index()
    {
    }
}
 
class Child extends Father
{
    protected/private function index()
    {
       //访问权限提升 错误 
       //父类为public 则子类重写也只能为public
       //父类为protected 则子类可为public/protected
       //父类为private 则子类public/protected/private皆可
    }
}

In fact, there are many interesting things about access level inheritance rules

private cannot be inherited in our common sense, and subclasses cannot get it, but its access level is already the highest, so you are The subclass can be written as private protected public, as if we have redefined a function ourselves. This is especially prominent before version 5.2, because versions before 5.2 do not need to keep the same number of parameters when inheriting and rewriting parent class methods, but After 5.3, restrictions in this area have been strengthened. The number of parameters must be the same as that of the parent class. Note:

When a subclass implements the abstract method of the parent class or a class implements the method of the

interface

, it is still an inheritance relationship and access is still pursued. The level can only lower the rules that cannot be upgraded, and abstract methods cannot be declared as private. Abstract-modified methods must be used for inheritance implementation, so they can only be public or protected. The method declaration of the interface must be public, and the methods declared in the interface must be public. It must be implemented by inheritance, and it can only be public. The class that implements this interface also specifies a method that is rewritten as a public type