Constructor method in PHP - Mini Project: Build & Apply

Constructor method

📖 Scenario: You are creating a simple PHP class to represent a Book in a library system.

🎯 Goal: Build a PHP class called Book that uses a constructor method to set the book's title and author when creating a new Book object.

📋 What You'll Learn

Create a class named Book

Add a constructor method named __construct that accepts two parameters: $title and $author

Inside the constructor, assign the parameters to the class properties $title and $author

Create an object of the Book class with the title '1984' and author 'George Orwell'

Print the book's title and author in the format: Title: 1984, Author: George Orwell

💡 Why This Matters

🌍 Real World

Constructors are used in real-world PHP applications to set up objects with initial data, like user profiles, products, or articles.

💼 Career

Understanding constructors is essential for PHP developers to write clean, reusable, and organized code in web development jobs.

1

Create the Book class with properties

Create a PHP class called Book with two public properties: $title and $author.

PHP

<?php

// Create class Book with public properties $title and $author
// Your code here

Hint

Use class Book { public $title; public $author; } to define the class and properties.

2

Add the constructor method

Inside the Book class, add a constructor method named __construct that takes two parameters: $title and $author. Assign these parameters to the class properties $this->title and $this->author.

PHP

<?php

class Book {
    public $title;
    public $author;

    // Add constructor method here
    // Your code here
}

Hint

Use public function __construct($title, $author) { $this->title = $title; $this->author = $author; }.

3

Create a Book object

Create a new object called $book from the Book class, passing '1984' as the title and 'George Orwell' as the author to the constructor.

PHP

title = $title;
        $this->author = $author;
    }
}

// Create a Book object named $book with title '1984' and author 'George Orwell'
// Your code here

Hint

Use $book = new Book('1984', 'George Orwell'); to create the object.

4

Print the book details

Print the book's title and author in this exact format: Title: 1984, Author: George Orwell using the $book object's properties.

PHP

title = $title;
        $this->author = $author;
    }
}

$book = new Book('1984', 'George Orwell');

// Print the book details here
// Your code here

Hint

Use print("Title: {$book->title}, Author: {$book->author}"); to show the output.

Practice

1. What is the main purpose of a constructor method in a PHP class?

easy

A. To print the object details

B. To delete an object from memory

C. To automatically set up an object when it is created

D. To create a new class inside the existing class

Solution

1. Step 1: Understand what a constructor does

   A constructor is a special method that runs automatically when an object is created.

2. Step 2: Identify the purpose of this automatic setup

   This setup usually initializes properties or runs code needed for the object to work properly.

3. Final Answer:

   To automatically set up an object when it is created -> Option C

4. Quick Check:

   Constructor = automatic setup [OK]

Hint: Constructor runs automatically on object creation [OK]

Common Mistakes:

• Thinking constructor deletes objects
• Confusing constructor with printing methods
• Assuming constructor creates new classes

2. Which of the following is the correct way to declare a constructor method in PHP?

easy

A. function __construct() {}

B. function construct() {}

C. function _construct() {}

D. function __destruct() {}

Solution

1. Step 1: Recall the special constructor name in PHP

   PHP uses the exact name __construct with two underscores at the start.

2. Step 2: Check each option for correct syntax

   Only function __construct() {} uses the correct spelling and underscores for the constructor.

3. Final Answer:

   function __construct() {} -> Option A

4. Quick Check:

   Constructor name = __construct [OK]

Hint: Constructor always named __construct with two underscores [OK]

Common Mistakes:

• Missing one or both underscores
• Using 'construct' without underscores
• Confusing constructor with destructor (__destruct)

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

class Car {
  public $color;
  public function __construct($color) {
    $this->color = $color;
  }
  public function getColor() {
    return $this->color;
  }
}
$myCar = new Car('red');
echo $myCar->getColor();

medium

A. red

B. Car

C. null

D. Error

Solution

1. Step 1: Understand constructor parameter usage

   The constructor sets the property color to the value passed ('red').

2. Step 2: Check what getColor() returns

   getColor() returns the color property, which was set to 'red'.

3. Final Answer:

   red -> Option A

4. Quick Check:

   Constructor sets color = 'red' [OK]

Hint: Constructor sets properties used later [OK]

Common Mistakes:

• Forgetting to pass argument to constructor
• Expecting class name as output
• Assuming property is null without initialization

4. Identify the error in this PHP class constructor code:

class Person {
  public $name;
  public function __construct {
    $this->name = 'Alice';
  }
}

medium

A. Constructor name should be Person

B. Wrong property name

C. Missing semicolon after assignment

D. Missing parentheses after __construct

Solution

1. Step 1: Check constructor syntax

   In PHP, the constructor method must have parentheses even if no parameters are used.

2. Step 2: Identify the missing parentheses

   The code misses () after __construct, causing a syntax error.

3. Final Answer:

   Missing parentheses after __construct -> Option D

4. Quick Check:

   Constructor needs () even if empty [OK]

Hint: Always add () after __construct even if empty [OK]

Common Mistakes:

• Omitting parentheses in method declaration
• Thinking constructor name must match class
• Forgetting semicolon after statements

5. You want to create a PHP class Book that stores a title and author. The constructor should accept both values and store them. Which code correctly implements this?

hard

A. class Book {
public $title, $author;
public function Book($title, $author) {
$this->title = $title;
$this->author = $author;
}
}

B. class Book {
public $title;
public $author;
public function __construct($title, $author) {
$this->title = $title;
$this->author = $author;
}
}

C. class Book {
public $title;
public $author;
public function __construct() {
$title = '';
$author = '';
}
}

D. class Book {
public $title;
public $author;
public function __construct($title) {
$this->title = $title;
}
}

Solution

1. Step 1: Check constructor name and parameters

   PHP uses __construct with two parameters $title and $author, matching the requirement.

2. Step 2: Verify property assignments

   The code assigns both $title and $author to object properties using $this correctly.

3. Final Answer:

   class Book { public $title; public $author; public function __construct($title, $author) { $this->title = $title; $this->author = $author; } } -> Option B

4. Quick Check:

   Constructor with all needed parameters and assignments [OK]

Hint: Use __construct with all needed parameters and assign to properties [OK]

Common Mistakes:

• Using old-style constructor named after class
• Not passing all required parameters
• Not assigning parameters to properties