Differences between abstract class and interface in PHP

  1. In abstract classes this is not necessary that every method should be abstract. But in interface every method is abstract.
  2. Multiple and multilevel both type of inheritance is possible in interface. But single and multilevel inheritance is possible in abstract classes.
  3. Method of php interface must be public only. Method in abstract class in php could be public or protected both.
  4. In abstract class you can define as well as declare methods. But in interface you can only defined your methods.

Traits in PHP

One of the problems of PHP as a programming language is the fact that you can only have single inheritance. This means a class can only inherit from one other class.

However, a lot of the time it would be beneficial to inherit from multiple classes. For example, it might be desirable to inherit methods from a couple of different classes in order to prevent code duplication.

This problem can lead to class that has a long family history of inheritance which often does not make sense.

In PHP 5.4 a new feature of the language was added known as Traits. A Trait is kind of like a Mixin in that it allows you to mix Trait classes into an existing class. This means you can reduce code duplication and get the benefits whilst avoiding the problems of multiple inheritance.

PHP Traits?

A Trait is simply a group of methods that you want include within another class. A Trait, like an abstract class, cannot be instantiated on it’s own.

An example of a Trait could be:

You could then include this Trait within other classes like this:

Now if you were to create new objects out of these classes you would find that they both have the share() method available:

How do Traits work?

As you can see from the example above, both the Post and the Comment objects have the share() method available despite not having that method defined.

A Trait is basically just a way to “copy and paste” code during run time.

This means the Trait is copied in to the Post and Comment classes so when you instantiate a new instance, the share() method code will be available.

How are Traits different to Abstract classes?

A Trait is different to an Abstract class (What are Abstract classes?) because they do not rely on inheritance.

Imagine if the Post and the Comment class had to inherit from a Social class. We are most likely going to want to do more than just share posts and comments on social media websites, so we’ll probably end up with a complicated inheritance tree like this:

This complicated inheritance is pretty nasty, but it also adds complication when a simpler object does not have a similar inheritance structure. For example, if we had a Message object that shouldn’t allow social sharing, then this object would require a slightly different inheritance structure.

How are Traits different to Interfaces?

Traits kind of look a lot like Interfaces. Both Traits and interfaces are usually simple, concise and not much use without an actual implemented class. However the difference between the two is important.

An interface is a contract that says “this object is able to do this thing”, whereas a Trait is giving the object the ability to do the thing.

For example:

In this example we have a Sociable interface that states that the Post object is able to like() and share().

The Sharable Trait implements the share() method and the like() method is implemented in the Post class.

So as you can see we could type hint the Post object to see if it is sociable (it implements the Sociable interface), whilst the Trait defines a reusable method that we can then mix in to other similar classes:

Benefits of Traits?

The benefit of using Traits is that you reduce code duplication whilst preventing complicated class inheritance that might not make sense within the context of your application.

This allows you to define simple Traits that are clear and concise and then mix in that functionality where appropriate.

Drawbacks of Traits?

However with that being said, there are possible drawbacks when using Traits too.

Traits make it very easy to write bloated classes that have too much responsibility. A Trait is essentially a way to “copy and paste” code between classes. By having a way to very simply add another group of methods to a class, it’s very easy to diverge from the single responsibility principle.

Other drawbacks to using Traits are not being able to see all the methods of a class when looking at the source code as well as method conflicts or duplication of logic.

I think Traits, when used correctly, are a fantastic tool to have at our disposal. However, Traits can also be crutch for lazy programming. It’s very easy to just add a Trait to solve your immediate problem. Often composition is the better approach over inheritance or using a Trait.

What are typical situations for using Traits?

So what would be a typical situation when using a Trait would be a good idea?

Well, I think Traits are an excellent way to reuse a chunk of code between a set of similar classes that should not inherit from the same abstract class.

Using the social application from earlier, imagine we had objects for Post, Photo, Note, Message and Link. For the most part, these objects are fairly interchangeable within our system as they are typically created and interacted with between users.

However, Post, Photo, Note and Link are all objects that are publicly shareable between users, whereas Message objects are private messages that are not made public.


Inheritance in PHP

Inheritance is a concept in object oriented programming. With the help of inheritance we can get all property and method of one class in another class. Inheritance in php is introduced from php5 version.

Here I will explore about basics concept of inheritance  After basic we will discuss implementation of inheritance in php. 


Inheritance is nothing but a design principle in oop. By implementing inheritance you can inherit(or get) all properties and methods of one class to another class. The class who inherit feature of another class known as child class. The class which is being inherited is know as parent class. Concept of the inheritance in oop is same as inheritance in real world. For example, child inherits characteristics  of their parent. Same is here in oop. One class is inheriting characteristics of another class.

With the help of inheritance you can increase re-usability of code. Let us take an example in terms of generic programming practices. Suppose you are going to create classes to render different html tag(div, span, form, table etc).  Now you will create class with name html_div, html_span ,  html_form. You are creating different class because every element is different in nature. For example form has action and method and you will have different input element in form. But table will have tbody, tr, th and td.

Now just think for some moment. There are some element and their rendering is same in all element. For example all html mention above is having name, id, class attribute which is same. Also rendering of those element is also same. So in above case you can create parent class with name tagsDetails and you can inherit that class across all of your html tags like div, span, form. Following is the generic code structure of inheritance in oop taking your HTML attribute in consideration.

Above code is and example of basic inheritance in php. All method(protected and public) from tagDetails class is directly accessible in your class page class. In child class you no need to write rendering of id and name logic again and again. This really saves time and give some good modulations in the code.

Hope your basic understanding about inheritance is clear. Now let us move to implementation of inheritance in php.

Multilevel and Multiple inheritance in PHP

In php multilevel inheritance is possible but multiple inheritance is not possible. In simplified terms in php child class can not inherit more than one parent class. But hierarchical inheritance is possible in php. Hierarchical means Parent inherit property of grand parent class. Grand child inherit property of parent class. So in multilevel inheritance child can get some property of from grand parent class also.

Example of Multiple inheritance in PHP

Above code will not work in php. Because php is single inheritance language.

Example of Multilevel inheritance in PHP

This is very basic example of multilevel inheritance. In php it is possible to implement multilevel inheritance. In above example parent class is inheriting grand parent property. And and child is inheriting parent property. So child have some parent and grand parent property.

Static Methods and Property in Inheritance in PHP

As in our example of page class we have explored that we can use $this-> keyword to get all property and method of parent(tagsDetails) class. But if your parent or child method is static, then you can access static methods or properties using self and parent keyword. Also this is not necessary to make method static if you want to use self or parent keyword. This is very useful if your parent and child both method is having property or method with same name. If both classes having same property and you want to call specific property or method then you can use this keyword.

Self and parent in case of static methods:

Self and Parent without static


Overriding in PHP

Method Overriding in OOP ?

Basic meaning of overriding in oop is same as real word meaning. In real word meaning of overriding  phenomena of replacing the same parental behaviour in child. This is same in case of method overriding in oop. In oop meaning of overriding is to replace parent class method in child class. Or in simple technical word method overriding mean changing behaviour of the method. In oop overriding is process by which you can re-declare your parent class method in child class. So basic meaning of overriding in oop is to change behaviour of your parent class method.

Normally method overriding required when your parent class have some method, but in your child class you want the same method with different behaviour. By overriding of method you can complete change its behaviour from parent class. To implement method overriding in oop we commonly create same method in child class.

Overriding in php is very easy. As we know that overriding is process of modifying the inherited method. So in case of inheritance you only need to create method with same name in your child class which you want to override. Following is example of overriding of method in php.

In above example you are overriding function f2. While overriding you are free to change business logic, visibility and number of parameter.

For more detail about overloading and overriding in php you can read:

Overloading in PHP

Method Overloading in OOP ?

Overloading in oop is same as overloading in real word. In real word overloading means assigning extra work to same machine or person. In oop method overloading is same. By process of method overloading you are asking your method to some extra work. Or in some cases we can say some different work also.

Normally method overloading in oop is managed on the basis of the argument passed in function. We can achieve overloading in oop by providing different argument in same function.

Implementation of overriding can not be achieved by creating 2 function with same name and different argument in php. Because we can not create same name function more than 1 time in php class. To implement overloading we need to take help of magic method in php. In below section we will explore overloading.

Overloading in PHP

As we know that we can not implement overloading by create 2 function in with same name in class. So to implement overloading in php we will take help of magic method __call. Magic method __call invoked when method called by class object is not available in class. So here we will not create method exactly and will take help of __call method. Now call method will provide us 2 argument, 1st name of the method called and parameter of the function. Now with the help of either switch , case or if else we will implement overloading in php. Following is very simple example of overloading in php.

As in above class test magic method __call is implemented which is managing overloading

As we know that __call magic method invoked when method is not available in the class. So in case of above test class example we have not created function overlodedFunction. So whenever method overlodedFunction is called __call invoked. __call pass 2 variable, first  name of the called method and other is parameter passed in the called function.

Now in the __call function I have applied if condition to ensure that our business logic of overloading works only for overlodedFunction function. In if block we have counted number of argument in parameter and applied business logic.