I have the following classes
Abstract class duck
This class have flyBehavoir of type FlyBehavoir
Function to perform flying preformFly()
Function to set flyBehavoir setFlyBrhavoir(FlyBehavoir $flyBehavoir)
Class DonaldDuck extends Duck
in this class, I have a __construct method, inside this constructor, I instantiate new fly behavior FlyWithWings.
The problem is when I need to change flyBehavoir in the runtime via setFlyBrhavoir() method and set it to FlyWithRocket it does not change as long as flyBehavoir is private if I make it public it works fine. how can I do that?
thought that we can change any property in the superclass from the child class, as long as I access this private property vis setter.
below my attempt
<?php
//abstract class that defines what it takes to be a duck
//inside Duck we will have $flyBehavoir object of FlyBehavoir Type
abstract class Duck{
private $flyBehavoir;
public function preformFly(){
$flyBehavoir.fly();
}
public function setFlyBehavoir(FlyBehavoir $flyBehavoir){
$this->flyBehavoir = $flyBehavoir;
}
}
//creating type FlyBehavoir
interface FlyBehavoir{
function fly();
}
//this concrete class of type FlyBehavoir this will provide our ducks with the functionality they need to fly
class FlyWithWings implements FlyBehavoir{
public function fly(){
echo "I am Flying with my own Wings<br>";
}
}
//this concrete class of type FlyBehavoir this will provide our ducks with the functionality they need to fly
class FlyWithRocket implements FlyBehavoir{
public function fly(){
echo "I am the fastest duck ever, see my rockets wings <br>";
}
}
// creating our first duck and given it the ability to fly with wings
class DonaldDuck extends Duck{
public function __construct(){
$this->flyBehavoir = new FlyWithWings;
}
}
$donaldDuck = new DonaldDuck( ) ;
$donaldDuck->flyBehavoir->fly();
//changing behavoir in run time
$donaldDuck->setFlyBehavoir(new FlyWithRocket);
$donaldDuck->flyBehavoir->fly();
Output
I am Flying with my own Wings
I am Flying with my own Wings
A private property is not accessible in child classes.
class DonaldDuck extends Duck {
public function __construct(){
$this->flyBehavoir = new FlyWithWings;
}
}
For all intents and purposes, this class does not formally declare flyBehaviour at all, so $this->flyBehaviour in the constructor creates a new public property. You can see that clearly when var_dumping the object:
object(DonaldDuck)#1 (2) {
["flyBehavoir":"Duck":private]=>
NULL
["flyBehavoir"]=>
object(FlyWithWings)#2 (0) {
}
}
The parent's private property is a) separate, b) private to it and c) null since nobody has set it yet. Otherwise it would also not be possible for you to access $donaldDuck->flyBehavoir->fly() from without the class!
If you have a private property, you need to only let code of the same class act on it:
class DonaldDuck extends Duck {
public function __construct(){
$this->setFlyBehaviour(new FlyWithWings);
}
}
$donaldDuck = new DonaldDuck();
$donaldDuck->setFlyBehavoir(new FlyWithRocket);
$donaldDuck->preformFly();
This works as you expect, since you're using the correctly privileged methods to access the property. If you want to access the property directly in child classes, it needs to be protected (which then won't let you access it from outside the class though, it would have to be public for that).
Related
When developing in C#, and you had many classes that used the same exact code, you could rely on another class to hold the generic information, making it easier to modify these classes.
I was wondering if there was anything like that in PHP?
class Dog extends Animal {
private $animalManager
public function __construct(AnimalManager $animalManager) {
$this->animalManager = $animalManager;
}
}
class Cat extends Animal {
private $animalManager
public function __construct(AnimalManager $animalManager) {
$this->animalManager = $animalManager;
}
}
class Fish extends Animal {
private $animalManager
public function __construct(AnimalManager $animalManager) {
$this->animalManager = $animalManager;
}
}
class Animal {
// Nothing, yet...
}
What C# would allow you to do is, store the $animalManager and the constructor assignement in the 'Animal' class somehow, making it constant in 1 place if you ever needed to change it.
The thing is, PHP does this quite neatly.Every extending class inherits everything from the extended class. This means the parent's (in this case animal) construct will run whenever you call one of the extending classes.
However, you overwrite your parent's class when you call __construct() within the child. Therefore you'd need to specifically call parent::__construct() to run the parent constructor.
class Animal {
//Private vars can't be directly accessed by children.
//You'd have to create a function in the parent return it.
public $animalManager
//This function will automatically be called if you leave the
//constructor out of the extended class
public function __construct($animalManager) {
$this->animalManager = $animalManager;
}
//If you want $animalManager to be private
//Call like $fish->getAnimalManager();
//Though I do not see the use of this.
public function getAnimalManager(){
return $this->animalManager
}
}
class Fish extends Animal {
//You do not need to do this if you leave the construct out of this class
public function __construct($animalManager) {
parent::__construct($animalManager);
//Do whatever you like here
}
}
Example with only the parent constructor:
class Fish extends Animal {
//The parent's constructor is called automatically as it's not
//Being overwritten by this class
public function test(){
var_dump($this->animalManager);
}
}
Note that you would also not need to initiate the parent class seperately. Just call it like so;
$fish = new Fish(myAnimalManager);
$am = $fish->animalManager;
echo $am;
A draft has been added by Ben Scholzen for generics here.
But all I can see is type parameters and no wildcards. It supports generic functions and generic constructors. It also supports Bounds.
Unlike C# and Java, PHP will have its type arguments fully reified, which means we can reflectively know the run time parameter of desired function/constructor.
Backward compatibility is not a concern here, because type parameters and raw types can never be compatible. So the legacy code won't be compatible with Generics.
Key class has a non-abstract method getDescription() (for many purposes).
Key class is extended by (one of) "a child abstract class".
"A child abstract class" is extended by "a concrete class".
I want to force "a concrete class" to implement getDescription() method and try to redeclare it in "a child abstract class" as an abstract method, but fail.
So, is it possible to redeclare non-abstract method as abstract in php?
If not - how to force a concrete method to be implemented?
The key class. I need getDescription as declared in this way for many purposes.
abstract class beverage{
public $description = "Unknown beverage";
public function getDescription(){return $this->description;}
};
The abstract class, overriden getDescription() - but does not work.
abstract class condimentDecorator extends beverage {
//public abstract function getDescription();
};
Concrete class, which MUST reimpliment getDescription.
class milk extends condimentDecorator{
public $beverage;
public function __construct(beverage $beverage){$this->beverage = $beverage;}
public function getDescription(){return $this->beverage->getDescription().", Milk";}
};
is it possible to redeclare non-abstract method as abstract in php?
No, you can't do that in PHP
It seems that you are trying to implement a Decorator pattern.In such case the presented classes chain is over-complicated.
Decorator pattern is dedicated to add(extend) functionality to another class without changing its structure.The following is a classical and more optimal approach of implementing decorators:
abstract class Beverage {
public $description = "Unknown beverage";
public function getDescription(){
return $this->description;
}
}
class CondimentDecorator extends Beverage {
protected $beverage;
public function __construct(Beverage $beverage) {
$this->beverage = $beverage;
}
public function getDescription() {
return "Description:\t" . $this->beverage->getDescription() . " with condiment";
}
};
class Milk extends Beverage {
public function __construct($desc = "") {
$this->description = $desc;
}
}
$milk = new Milk('Milk beverage');
$milk_with_condiment = new CondimentDecorator($milk);
echo $milk_with_condiment->getDescription();
The output:
Description: Milk beverage with condiment
I think the main problem is how you're implementing this.
If you've an class that already implements a method all it's children will by default implement it.
So lets say you've the following:
Class A {
public function niceFunction() {return "some awesome return with potato"; }
}
Class B extends A{
//it already has niceFunction
}
Class Avocado extends B {
// it also already has NiceFunction
}
So what you want to do is overwrite the default function.
I think you should take a time and re-think if the structure is correct.
The condimentDecorator couldn't be a interface?
Editd:
My suggestion would be do something Like this:
Interface Descritible()
{
public function getDescription();
}
class beverage implements Descritible{
//do the stuff you need to do
// It must have getDescription() cuz it implements Descritible
}
abstract class A implements Descritible{}
class Avocado extends A {
//It'll not have a default implementation of getDescription
//so it'll have to implement it.
}
So then the Class avocado will need to implements getDescription as Beverage would've as well, and you should be conflict free.
I have a parent class that has a public function that is final. Is it possible to disallow access to this method in a derived class? Other classes that derive from the parent class need to still be able to call it.
class ParentClass {
final public function test() {
}
}
class ChildClass extends ParentClass {
}
class ChildClass2 extends ParentClass {
}
$child = new ChildClass();
$child2 = new ChildClass2();
// make this illegal:
$child->test();
// but not this:
$child2->test();
When you inherit from class it means that derived class is a class that inherits. It means that it has exact the same base functionality that can be expanded, overriden and so on. If it makes no sense that derived class had method that is defined in parent class means that derived class is not a class that it derives.
For real world example let's say you have class FlyingMachine that has method Fly and Move, it would not be logical if you derived class Car from FlyingMachine because cars don't fly, while deriving class AirPlane from mentioned base class is perfectly fine. But it would be logical if you had base class Machine that had method Move and car was derived from this class Car : Machine (car is a machine, right?), FlyingMachine is a machine too so FlyingMachine : Machine is perfectly fine and since air-plane is a flying machine AirPlane : FlyingMachine makes sense.
For your given example this should be something like:
abstract class VeryBaseClass {
public function MethodThatIsLogicalForEveryDerivedClass() {}
}
abstract class BaseClass extends VeryBaseClass {
public function SomeOtherFunctionThatMakesSenseOnlyForSomeClasses() {}
}
class ClassThatShouldNotHaveSpecificFunctionDefinedInBaseClass extends VeryBaseClass{}
class ClassThatShouldHaveSomeOtherMethod extends BaseClass {}
Edit:
If there's a functionality that several derived classes need but for some of them it should be public and for some of them not. You should define in base class this method as protected (derived class can access one but from outside impossible). And in derived class that require that this method was public make another method and call parent's method. E.g.:
abstract class Car { protected function Shift() {} }
class ManualCar extends Car {
public function Shift() { parent::Shift(); }
}
class AutomaticCar extends Car {
//Some implementation of automatic car that uses protected Shift method
}
Little demo
How about checking for that class in the method, and throwing an exception if it's the disallowed class:
class ParentClass {
final public function test() {
if (get_class($this) == "ChildClass")
throw new Exception("ChildClass cannot call test()")
}
}
NB: this is fairly evil
In other OO languages like Java we can override a function, possible using keywords/annotations like implements, #override etc.
Is there a way to do so in PHP? I mean, for example:
class myClass {
public static function reImplmentThis() { //this method should be overriden by user
}
}
I want user to implement their own myClass::reImplementThis() method.
How can I do that in PHP? If it is possible, can I make it optional?
I mean, if the user is not implementing the method, can I specify a default method or can I identify that the method is not defined (can I do this using method_exists)?
<?php
abstract class Test
{
abstract protected function test();
protected function anotherTest() {
}
}
class TestTest extends Test
{
protected function test() {
}
}
$test = new TestTest();
?>
This way the class TestTest must override the function test.
Yes, there is. You have the option to override a method by extending the class and defining a method with the same name, function signature and access specifier (either public or protected) it had in the base class. The method should not be declared abstract in the base class or you will be required to implement it in the derived class. In you example it would look something like this:
class MyClass {
public static function reImplmentThis() { //this method should be overriden by user
}
}
class MyDerivedClass extends MyClass {
public static function reImplmentThis() { //the method you want to call
}
}
If the user does not overrides it, MyDerivedClass will still have a reImplmentThis() method, the one inherited from MyClass.
That said, you need to be very careful when invoking extended static methods from your derived class to stay out of trouble. I encourage you to refactor your code to extend instance methods unless you have a very specific need to extend static classes. And if you decide there is no better way than extending static classes please be sure to understand Late Static Binding pretty well.
Yes, its possible to check if the method is implemented or not and get a whole lot more of information about a class using PHP Reflection.
This touches on several OOP subjects.
First, simply overriding an method declared in a parent class is as simple as re-declaring the method in an inheriting class.
E.g:
class Person {
public function greet(string $whom) {
echo "hello $whom!";
}
}
class Tommy extends Person {
public function greet(string $whom = "everyone") {
echo "Howdy $whom! How are you?";
}
}
$a = new Tommy();
$a->greet('World');
// outputs:
// Howdy World! How are you?
If on the overriding method you wan to reuse the logic of the overriden one, it's just a matter of calling the parent's method from the extending class::
class Tommy
{
public function greet(string $whom)
{
// now with more emphasis!!!
echo parent::greet(strtoupper($whom)) . "!!!!";
}
}
Now Tommy::greet() calls Person::greet(), but modifies the result before returning it.
One thing to note is that overriding methods have to be compatible with the overriden one: the method visibility can't be more restrictive than the original one (it's OK to increase visibility), and the number and type of required arguments can't conflict with the original delcaration.
This works, because the type of the arguments does not clash with the original, and we have less required arguments than on the parent:
class Leo extends Person {
public function greet(string $whom = "gorgeous", string $greet = "Whatsup" ) {
echo "$greet $whom. How are you?";
}
}
But this doesn't, since there are additional required arguments. This would make impossible to switch the original class for this one transparently, and thus would throw a Warning:
class BadBob extends Person {
public function greet(string $whom, string $greet ) {
echo "$greet $whom. How are you?";
}
}
Additionally, you mention in your question that "this method should be overriden by the user". If you require client classes to actually implement the method, you have a couple of options:
Abstract classes & methods
These are methods where the implementation is left empty, and that extending classes have to implement to be valid. In we changed our original class Person to:
abstract class Person {
public function greet(string $whom) {
echo "hello $whom!";
}
public abstract function hide();
}
Since now the class contains an abstract method, it needs to be declared as an abstract class as well.
Now it is not possible to instantiate Person directly, you can only extend it in other classes.
Now all our existing Person extending classes would be wrong, and trying to execute the previous code would throw a fatal error.
An example of a valid class extending Person now would be:
class Archie extends Person {
public function hide() {
echo "Hides behind a bush";
}
}
Any class that extends Person must declare a public hide() method.
Interfaces
Finally, you mention interfaces. Interfaces are contracts that implementing classes have to fulfill. They declare a group of public methods without an implementation body.
E.g.:
interface Policeman {
public function arrest(Person $person) : bool;
public function help($what): bool;
}
Now we could have class that extended Person and implemented Policeman:
class Jane extends Person implements Policeman {
public function hide() {
echo "Jane hides in her patrol-car";
}
public function arrest(Person $person): bool{
// implement arrest method
return false;
}
public function shoot($what): bool {
// implements shoot() method
return false;
}
}
Importantly, while it's possible to extend only one class (there is no multiple inheritance in PHP), it is possible to implement multiple interfaces, and the requirements for each of those have to be fulfilled for the class to be valid.
If I have an abstract class like this:
abstract class MyApp
{
public function init()
{
$this->stuff = $this->getStuff();
}
public function getStuff()
{
return new BlueStuff();
}
}
And then I have a class that extends from this abstract class like this:
class MyExtendedClass extends MyApp
{
public function init()
{
parent::init();
}
public function getStuff()
{
return new RedStuff();
}
}
If I do:
$myobj = new MyExtendedClass();
$myobj->init();
Why does the method getStuff from the child class get called? Isn't $this in the context of the abstract class? If so, shouldn't the method of the abstract class get called?
Thanks!
New answer
In PHP you can use subclasses as if all methods in the parent class that don't exist in the subclass have been copied to the subclass. So your example would be the same as:
class MyExtendedClass extends MyApp {
public function init() {
$this->stuff = $this->getStuff();
}
public function getStuff() {
return new RedStuff();
}
}
Just think of the subclass as having all code of the parent class and you're normally all right. There is one exception to this rule: properties. A private property of a class can only be accessed by that class, subclasses can't access the private properties of parent classes. In order to do that you need to change the private property into a protected property.
Original answer
Abstract classes in PHP are just like regular classes with one big difference: they can't get initiated. This means you can't do new AbstractClass();.
Since they work exactly like regular classes for everything else, this also is the case for extending classes. This means that PHP first tries to find the method in the initiated class, and only looks in the abstract classes if it doesn't exist.
So in your example this would mean that the getStuff() method from MyExtendedClass is called. Furthermore, this means you can leave out the init() method in MyExtendedClass.