Final keyword in PHP

In PHP, the final keyword is used to restrict the inheritance of a class or the overriding of a method. When a class or method is declared as final, it cannot be extended or overridden by any child class.

• Final Class: A final class cannot be extended by any other class. If we try to extend a final class, a fatal error will occur. For example:

final class MyClass {
   // class code
}

class MyChildClass extends MyClass {
   // error: MyClass cannot be extended
}

• Final Method: A final method cannot be overridden by any child class. If we try to override a final method, a fatal error will occur. For example:

class MyClass {
   final public function myMethod() {
      // method code
   }
}

class MyChildClass extends MyClass {
   public function myMethod() {
      // error: myMethod() cannot be overridden
   }
}

• Final Variable: In PHP, we cannot declare a variable as final. However, we can achieve the same functionality by using the const keyword to define a constant. Constants cannot be changed once they are defined. For example:

class MyClass {
   const MY_CONSTANT = 10;
}

echo MyClass::MY_CONSTANT; // output: 10

In conclusion, the final keyword in PHP is used to restrict the inheritance of a class or the overriding of a method. It helps to ensure that certain classes or methods cannot be modified or extended, which can be useful in preventing unexpected behavior in our code.