What should you pay attention to when overriding parent class methods in PHP?

When rewriting parent class methods in PHP, please note: 1. Class methods modified with the final keyword cannot be overridden by subclasses; 2. Whether PHP overrides parent class methods will only be judged based on whether the method names are consistent; 3. When rewriting, the access level can only be equal to or looser than the parent class, and the access level cannot be increased.

Class method rewriting rules in PHP

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1. Class methods modified by final cannot be overridden by subclasses

Class methods modified by final cannot be overridden by subclasses. Even if the final private method cannot be inherited, subclasses still cannot rewrite it.

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 rewrites the parent class method will only be judged based on whether the method name is consistent (the number of parameters of the rewritten parent class method after 5.3 must be consistent)

This does not mean method parameters It has no effect, PHP has no overloading mechanism. Therefore, whether it is overridden or not will only be judged by the method name (C/C is considered to be overriding only if the method names are not only the same, but also the parameters are the same, otherwise it is overloaded, that is, the state of a polymorphic function is newly defined).

When the method names are the same, it is considered to be overriding the parent class method. In 5.2, the parameters can be different. 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
    }
}

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3. When rewriting, the access level can only be equal to or looser than the parent class, and the access level cannot be increased

The public method of the parent class cannot be overridden as protected or private by the subclass, and the protected method cannot be overridden as private.

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
    }
}

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