{"id":713,"date":"2021-03-26T02:30:30","date_gmt":"2021-03-26T02:30:30","guid":{"rendered":"https:\/\/phptutorial.net\/?page_id=713"},"modified":"2025-04-07T11:28:28","modified_gmt":"2025-04-07T11:28:28","slug":"php-polymorphism","status":"publish","type":"page","link":"https:\/\/www.phptutorial.net\/php-oop\/php-polymorphism\/","title":{"rendered":"PHP Polymorphism"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you will learn about the polymorphism concept in object-oriented programming. And you’ll also learn how to implement polymorphism in PHP using abstract classes or interfaces.<\/p>\n\n\n\n

What is polymorphism? #<\/a><\/h2>\n\n\n\n

Polymorphism is a Greek word that literally means many forms. In object-oriented programming, polymorphism is closely related to inheritance<\/a>. <\/p>\n\n\n\n

Polymorphism allows objects<\/a> of different classes to respond differently based on the same message. <\/p>\n\n\n\n

To implement polymorphism in PHP, you can use either abstract classes<\/a> or interfaces<\/a>.<\/p>\n\n\n\n

Polymorphism helps you create a generic framework that takes the different object types that share the same interface. <\/p>\n\n\n\n

Later, when you add a new object type to the system, you don’t need to change the framework to accommodate the new object type as long as it implements the same interface.<\/p>\n\n\n\n

By using polymorphism, you can reduce coupling and increase code reusability.<\/p>\n\n\n\n

PHP polymorphism using an abstract class #<\/a><\/h2>\n\n\n\n

First, define an abstract class named Person<\/code> that has an abstract method called greet()<\/code>.<\/p>\n\n\n

<?php<\/span>\n\nabstract<\/span> class<\/span> Person<\/span>\n<\/span>{\n\tabstract<\/span> public<\/span> function<\/span> greet<\/span>()<\/span><\/span>;\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, define the English<\/code>, German<\/code>, and French<\/code> classes that extend the Person<\/code> class. The greet()<\/code> method of each class returns a different greeting message.<\/p>\n\n\n
<?php<\/span>\n\/\/ ...<\/span>\nclass<\/span> English<\/span> extends<\/span> Person<\/span>\n<\/span>{\n\tpublic<\/span> function<\/span> greet<\/span>()<\/span>\n\t<\/span>{\n\t\treturn<\/span> 'Hello!'<\/span>;\n\t}\n}\n\nclass<\/span> German<\/span> extends<\/span> Person<\/span>\n<\/span>{\n\tpublic<\/span> function<\/span> greet<\/span>()<\/span>\n\t<\/span>{\n\t\treturn<\/span> 'Hallo!'<\/span>;\n\t}\n}\n\nclass<\/span> French<\/span> extends<\/span> Person<\/span>\n<\/span>{\n\tpublic<\/span> function<\/span> greet<\/span>()<\/span>\n\t<\/span>{\n\t\treturn<\/span> 'Bonjour!'<\/span>;\n\t}\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, define a function called greeting()<\/code> that accepts an array of Person<\/code> objects and calls the greet()<\/code> method of each object:<\/p>\n\n\n
<?php<\/span>\n\/\/...<\/span>\nfunction<\/span> greeting<\/span>($people)<\/span>\n<\/span>{\n\tforeach<\/span> ($people as<\/span> $person) {\n\t\techo<\/span> $person->greet() . '<br>'<\/span>;\n\t}\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Fourth, define an array of objects of the English<\/code>, German<\/code>, and French<\/code> classes and pass it to the greeting()<\/code> function:<\/p>\n\n\n
<?php<\/span>\n\/\/...<\/span>\n$people = [\n\tnew<\/span> English(),\n\tnew<\/span> German(),\n\tnew<\/span> French()\n];\n\ngreeting($people);<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Hello!\nHallo!\nBonjour!<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Due to the specific implementation of the greet()<\/code> method in each class, these objects return different greeting messages.<\/p>\n\n\n\n
The following class diagram illustrates the relationships between the classes:<\/p>\n\n\n\n
\"PHP<\/figure><\/div>\n\n\n\n
Later, if you want to create a new class that extends the Person<\/code> class, you don’t need to change the greeting()<\/code> function. <\/p>\n\n\n\n
For example, you can define a new class called American<\/code> that extends the Person<\/code> class:<\/p>\n\n\n
<?php<\/span>\n\/\/ ...<\/span>\nclass<\/span> American<\/span> extends<\/span> Person<\/span>\n<\/span>{\n\tpublic<\/span> function<\/span> greet<\/span>()<\/span>\n\t<\/span>{\n\t\treturn<\/span> 'Hi!'<\/span>;\n\t}\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
And use the object of the American<\/code> class in the greeting()<\/code> function as follows:<\/p>\n\n\n
\n<?php<\/span>\n\/\/ ...<\/span>\n$people = [\n\tnew<\/span> English(),\n\tnew<\/span> German(),\n\tnew<\/span> French(),\n\tnew<\/span> American()\n];\n\ngreeting($people);<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Hello!\nHallo!\nBonjour!\nHi!<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
PHP polymorphism using an interface #<\/a><\/h2>\n\n\n\n
The following example is the same as the above except that it uses an interface instead of an abstract class.<\/p>\n\n\n\n
First, define an interface called Greeting<\/code> that has the greet()<\/code> method. The greet()<\/code> method returns a greeting message:<\/p>\n\n\n
<?php<\/span>\n\ninterface<\/span> Greeting<\/span>\n<\/span>{\n\tpublic<\/span> function<\/span> greet<\/span>()<\/span><\/span>;\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, define the English<\/code>, German<\/code>, and French<\/code> classes that implement the Greeting<\/code> interface:<\/p>\n\n\n
\n<?php<\/span>\n\/\/ ...<\/span>\nclass<\/span> English<\/span> implements<\/span> Greeting<\/span>\n<\/span>{\n\tpublic<\/span> function<\/span> greet<\/span>()<\/span>\n\t<\/span>{\n\t\treturn<\/span> 'Hello!'<\/span>;\n\t}\n}\n\nclass<\/span> German<\/span> implements<\/span> Greeting<\/span>\n<\/span>{\n\tpublic<\/span> function<\/span> greet<\/span>()<\/span>\n\t<\/span>{\n\t\treturn<\/span> 'Hallo!'<\/span>;\n\t}\n}\n\nclass<\/span> French<\/span> implements<\/span> Greeting<\/span>\n<\/span>{\n\tpublic<\/span> function<\/span> greet<\/span>()<\/span>\n\t<\/span>{\n\t\treturn<\/span> 'Bonjour!'<\/span>;\n\t}\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, define the greeting()<\/code> function that accepts an array of objects that implements the Greeting<\/code> interface:<\/p>\n\n\n
<?php<\/span>\n\/\/ ...<\/span>\nfunction<\/span> greeting<\/span>($greeters)<\/span>\n<\/span>{\n\tforeach<\/span> ($greeters as<\/span> $greeter) {\n\t\techo<\/span> $greeter->greet() . '<br>'<\/span>;\n\t}\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Finally, define an array of the Greeting<\/code> objects and pass it to the greeting()<\/code> function:<\/p>\n\n\n
\n<?php<\/span>\n\/\/ ...<\/span>\n$greeters = [\n\tnew<\/span> English(),\n\tnew<\/span> German(),\n\tnew<\/span> French(),\n];\n\ngreeting($greeters);<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
Hello!\nHallo!\nBonjour!<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
The following class diagram shows the relationships between the interface and classes:<\/p>\n\n\n\n
\"\"<\/figure><\/div>\n\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
  • Polymorphism allows objects of different classes to respond differently to the same message.<\/li>
  • Use interfaces or abstract classes to implement polymorphism in PHP.<\/li><\/ul>\n
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