Method overriding in PHP - Mini Project: Build & Apply

Method overriding

📖 Scenario: Imagine you are creating a simple system for different types of vehicles. Each vehicle can describe itself, but some vehicles have special descriptions.

🎯 Goal: You will create a base class with a method, then create a child class that overrides this method to provide a special message.

📋 What You'll Learn

Create a base class called Vehicle with a method describe() that returns the string "This is a vehicle."

Create a child class called Car that extends Vehicle.

Override the describe() method in Car to return the string "This is a car."

Create an object of Car and print the result of calling its describe() method.

💡 Why This Matters

🌍 Real World

Method overriding helps customize behavior in different types of objects, like vehicles, animals, or employees, while sharing common features.

💼 Career

Understanding method overriding is essential for object-oriented programming, which is widely used in software development jobs to build flexible and reusable code.

1

Create the base class Vehicle

Create a class called Vehicle with a public method describe() that returns the string "This is a vehicle."

PHP

<?php

// Create class Vehicle with method describe()
// Your code here

Hint

Use class Vehicle {} and inside it define public function describe() that returns the string.

2

Create the child class Car

Create a class called Car that extends Vehicle.

PHP

<?php

class Vehicle {
    public function describe() {
        return "This is a vehicle.";
    }
}

// Create class Car that extends Vehicle
// Your code here

Hint

Use class Car extends Vehicle {} to create the child class.

3

Override the describe() method in Car

Inside the Car class, override the describe() method to return the string "This is a car."

PHP

<?php

class Vehicle {
    public function describe() {
        return "This is a vehicle.";
    }
}

class Car extends Vehicle {
    // Override describe() method
    // Your code here
}

Hint

Define public function describe() inside Car and return the new string.

4

Create Car object and print description

Create an object called $myCar of class Car and print the result of calling $myCar->describe().

PHP

<?php

class Vehicle {
    public function describe() {
        return "This is a vehicle.";
    }
}

class Car extends Vehicle {
    public function describe() {
        return "This is a car.";
    }
}

// Create object $myCar and print description
// Your code here

Hint

Create the object with new Car() and use print() to show the description.

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