Method overriding in PHP

Introduction

Method overriding lets a child class change how a method from its parent works. This helps customize behavior without changing the parent.

You want a child class to do something different when calling a method that exists in the parent.

You have a general method in a parent class but need specific versions in child classes.

You want to reuse code but still change small parts of how it works in different classes.

Syntax

PHP

<?php
class ParentClass {
    public function methodName() {
        // parent method code
    }
}

class ChildClass extends ParentClass {
    public function methodName() {
        // child method code overrides parent
    }
}
?>

The child method must have the same name as the parent method to override it.

The child method can call the parent method using parent::methodName() if needed.

Examples

The Dog class changes the sound method to print "Bark" instead of "Some sound".

PHP

<?php
class Animal {
    public function sound() {
        echo "Some sound";
    }
}

class Dog extends Animal {
    public function sound() {
        echo "Bark";
    }
}
?>

The Car class overrides start but also calls the parent method first.

PHP

<?php
class Vehicle {
    public function start() {
        echo "Vehicle started";
    }
}

class Car extends Vehicle {
    public function start() {
        parent::start();
        echo " and car engine is running";
    }
}
?>

Sample Program

This program shows how ColorPrinter changes the message printed by overriding printMessage from Printer.

PHP

<?php
class Printer {
    public function printMessage() {
        echo "Printing from Printer";
    }
}

class ColorPrinter extends Printer {
    public function printMessage() {
        echo "Printing in color";
    }
}

$printer = new Printer();
$printer->printMessage();
echo "\n";

$colorPrinter = new ColorPrinter();
$colorPrinter->printMessage();
?>

Important Notes

Method overriding only works with inheritance (child and parent classes).

Access modifiers like public or protected should be compatible between parent and child methods.

Summary

Method overriding lets child classes change parent methods.

Use the same method name in child to override.

You can still call the parent method inside the child method with parent::methodName().

Practice

1. What does method overriding allow a child class to do in PHP?

easy

A. Change the behavior of a method inherited from the parent class

B. Create a new method with a different name

C. Prevent the parent class from being instantiated

D. Automatically call all parent methods

Solution

1. Step 1: Understand method overriding concept

   Method overriding means a child class uses the same method name as the parent to change its behavior.

2. Step 2: Identify what overriding does

   It replaces or modifies the parent's method behavior in the child class.

3. Final Answer:

   Change the behavior of a method inherited from the parent class -> Option A

4. Quick Check:

   Method overriding = change parent method behavior [OK]

Hint: Overriding means same method name, new behavior [OK]

Common Mistakes:

• Thinking overriding creates new methods with different names
• Confusing overriding with inheritance itself
• Believing overriding prevents parent instantiation

2. Which of the following is the correct syntax to override a method named greet in a child class in PHP?

easy

A. function greetChild() { /* new code */ }

B. function greet() { /* new code */ }

C. override function greet() { /* new code */ }

D. parent::greet() { /* new code */ }

Solution

1. Step 1: Recall method overriding syntax

   To override, define a method with the same name in the child class.

2. Step 2: Check options for correct syntax

   Only function greet() { /* new code */ } defines function greet() correctly without extra keywords.

3. Final Answer:

   function greet() { /* new code */ } -> Option B

4. Quick Check:

   Same method name in child = override [OK]

Hint: Use same method name in child class to override [OK]

Common Mistakes:

• Adding 'override' keyword which PHP does not use
• Changing method name to something else
• Trying to call parent method syntax incorrectly

3. What will be the output of this PHP code?

class ParentClass {
  function sayHello() {
    echo "Hello from Parent";
  }
}
class ChildClass extends ParentClass {
  function sayHello() {
    echo "Hello from Child";
  }
}
$obj = new ChildClass();
$obj->sayHello();

medium

A. Hello from ParentChild

B. Hello from Parent

C. Hello from Child

D. Error: Method not found

Solution

1. Step 1: Identify method overriding in ChildClass

   ChildClass defines sayHello() which overrides ParentClass method.

2. Step 2: Check which method is called

   Creating ChildClass object calls ChildClass's sayHello(), printing "Hello from Child".

3. Final Answer:

   Hello from Child -> Option C

4. Quick Check:

   Child method overrides parent = "Hello from Child" [OK]

Hint: Child method runs if overridden, not parent [OK]

Common Mistakes:

• Expecting parent method output instead of child
• Thinking both outputs print together
• Assuming error due to method name clash

4. Find the error in this PHP code that tries to override a method:

class Base {
  function show() {
    echo "Base";
  }
}
class Derived extends Base {
  function show() {
    parent.show();
    echo " Derived";
  }
}
$obj = new Derived();
$obj->show();

medium

A. Class Derived must declare show() as public

B. Cannot override methods in PHP

C. Missing return statement in show()

D. Incorrect syntax to call parent method; should use parent::show()

Solution

1. Step 1: Identify how parent method is called

   The code uses parent.show() which is invalid syntax in PHP.

2. Step 2: Correct syntax for calling parent method

   PHP requires parent::show() to call the parent's method inside child.

3. Final Answer:

   Incorrect syntax to call parent method; should use parent::show() -> Option D

4. Quick Check:

   Call parent method with parent::method() [OK]

Hint: Use parent::method() to call parent method inside child [OK]

Common Mistakes:

• Using dot (.) instead of :: to call parent method
• Thinking overriding is not allowed
• Forgetting to call parent method when needed

5. Given these classes, what will be the output?

class Animal {
  function sound() {
    echo "Some sound";
  }
}
class Dog extends Animal {
  function sound() {
    parent::sound();
    echo " and Bark";
  }
}
class Puppy extends Dog {
  function sound() {
    echo "Yip";
  }
}
$pet = new Puppy();
$pet->sound();

hard

A. Yip

B. Some sound and Bark and Yip

C. Some sound and Bark

D. Error: Cannot override multiple times

Solution

1. Step 1: Trace method calls for Puppy object

   Puppy overrides sound() and only echoes "Yip" without calling parent.

2. Step 2: Understand overriding chain

   Since Puppy method does not call parent::sound(), Dog and Animal methods are not executed.

3. Final Answer:

   Yip -> Option A

4. Quick Check:

   Child override without parent call = only child output [OK]

Hint: If child method skips parent call, only child output shows [OK]

Common Mistakes:

• Assuming all parent methods run automatically
• Expecting combined outputs without explicit parent calls
• Thinking multiple overrides cause errors