__construct and __destruct in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a constructor method in a PHP class.

PHP

<?php
class Car {
    public function [1]() {
        echo "Car created.";
    }
}
?>

Drag options to blanks, or click blank then click option'

A__construct

B__destruct

Cconstructor

Dinit

Attempts:

3 left

💡 Hint

Common Mistakes

Using __destruct instead of __construct

Using a method name without underscores

Using 'constructor' as method name

The __construct method is the special function called automatically when a new object is created.

2fill in blank

medium

Complete the code to define a destructor method in a PHP class.

PHP

<?php
class Car {
    public function [1]() {
        echo "Car destroyed.";
    }
}
?>

Drag options to blanks, or click blank then click option'

A__construct

B__destruct

Cdestroy

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using __construct instead of __destruct

Using method names like 'destroy' or 'delete'

Forgetting the double underscores

The __destruct method is called automatically when an object is destroyed or script ends.

3fill in blank

hard

Fix the error in the constructor method name.

PHP

<?php
class Bike {
    public function [1]() {
        echo "Bike created.";
    }
}
?>

Drag options to blanks, or click blank then click option'

Aconstruct

B__destruct

Cinit

D__construct

Attempts:

3 left

💡 Hint

Common Mistakes

Missing underscores in method name

Using __destruct instead of __construct

Using 'construct' without underscores

The constructor method must be named __construct with two underscores.

4fill in blank

hard

Fill both blanks to create a class with constructor and destructor methods that print messages.

PHP

<?php
class House {
    public function [1]() {
        echo "House built.";
    }
    public function [2]() {
        echo "House demolished.";
    }
}
?>

Drag options to blanks, or click blank then click option'

A__construct

B__destruct

Cdestroy

Dbuild

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping constructor and destructor names

Using 'destroy' or 'build' instead of magic methods

Missing underscores

The constructor is __construct and the destructor is __destruct.

5fill in blank

hard

Fill all three blanks to create a class that sets a property in the constructor, prints it, and then prints a message in the destructor.

PHP

<?php
class Book {
    public $title;
    public function [1]($name) {
        $this->title = $name;
    }
    public function printTitle() {
        echo $this->[2];
    }
    public function [3]() {
        echo "Book closed.";
    }
}
?>

Drag options to blanks, or click blank then click option'

A__construct

Btitle

C__destruct

DprintTitle

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method names for constructor or destructor

Accessing property with wrong name

Forgetting $this-> when accessing property

The constructor is __construct, the property is title, and the destructor is __destruct.

Practice

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

easy

A. To pause the program execution

B. To delete an object from memory

C. To print the object details

D. To initialize an object when it is created

Solution

1. Step 1: Understand the role of __construct

   The __construct method is automatically called when a new object is created from a class.

2. Step 2: Identify its purpose

   It is used to set up or initialize the object, like setting initial values or preparing resources.

3. Final Answer:

   To initialize an object when it is created -> Option D

4. Quick Check:

   __construct = initialize object [OK]

Hint: Constructor runs at object creation to set it up [OK]

Common Mistakes:

• Confusing __construct with __destruct
• Thinking __construct deletes objects
• Assuming __construct prints output

2. Which of the following is the correct syntax to define a destructor method in a PHP class?

easy

A. function __destruct() {}

B. function destruct() {}

C. function __delete() {}

D. function destructor() {}

Solution

1. Step 1: Recall PHP destructor syntax

   PHP uses the special method named __destruct with two underscores to define destructors.

2. Step 2: Match the correct syntax

   The correct syntax is function __destruct() {}. Other options are invalid method names for destructors.

3. Final Answer:

   function __destruct() {} -> Option A

4. Quick Check:

   Destructor syntax = __destruct() [OK]

Hint: Destructor method always named __destruct() with double underscores [OK]

Common Mistakes:

• Using single underscore or wrong method name
• Forgetting parentheses in method definition
• Confusing destructor with constructor syntax

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

class Test {
  function __construct() {
    echo "Start ";
  }
  function __destruct() {
    echo "End";
  }
}
$obj = new Test();
echo "Middle ";

medium

A. Middle Start End

B. Start End Middle

C. Start Middle End

D. End Start Middle

Solution

1. Step 1: Trace constructor execution

   When $obj = new Test(); runs, __construct prints "Start ".

2. Step 2: Trace echo after object creation

   Next, echo "Middle "; prints "Middle ".

3. Step 3: Understand destructor timing

   Destructor __destruct runs when script ends or object is destroyed, printing "End" last.

4. Final Answer:

   Start Middle End -> Option C

5. Quick Check:

   Constructor -> echo -> Destructor = Start Middle End [OK]

Hint: Constructor prints first, destructor last after script ends [OK]

Common Mistakes:

• Assuming destructor runs immediately after constructor
• Mixing order of printed words
• Forgetting destructor runs at script end

4. Identify the error in this PHP class code:

class Sample {
  function __construct {
    echo "Hello";
  }
  function __destruct() {
    echo "Goodbye";
  }
}
$obj = new Sample();

medium

A. Destructor method name is incorrect

B. Missing parentheses in __construct method definition

C. Class name must be capitalized

D. Missing semicolon after echo statements

Solution

1. Step 1: Check constructor syntax

   The __construct method is missing parentheses () after its name, which is required in PHP.

2. Step 2: Verify other parts

   The destructor name and syntax are correct, class name capitalization is not mandatory, and echo statements have semicolons.

3. Final Answer:

   Missing parentheses in __construct method definition -> Option B

4. Quick Check:

   Constructor needs () after name [OK]

Hint: Always add () after method names, even if no parameters [OK]

Common Mistakes:

• Omitting parentheses in method definitions
• Thinking destructor name is wrong
• Believing class names must be capitalized

5. You want to create a PHP class that opens a file when an object is created and closes it automatically when the object is destroyed. Which code snippet correctly uses __construct and __destruct for this purpose?

hard

A. class FileHandler {
private $file;
function __construct($filename) {
$this->file = fopen($filename, 'r');
}
function __destruct() {
fclose($this->file);
}
}

B. class FileHandler {
private $file;
function __construct() {
fclose($this->file);
}
function __destruct() {
$this->file = fopen('file.txt', 'r');
}
}

C. class FileHandler {
function __construct($filename) {
fclose($filename);
}
function __destruct() {
fopen($filename, 'r');
}
}

D. class FileHandler {
private $file;
function __construct($filename) {
$this->file = fopen($filename, 'r');
}
function __destruct() {
echo 'File closed';
}
}

Solution

1. Step 1: Analyze constructor for opening file

   class FileHandler { private $file; function __construct($filename) { $this->file = fopen($filename, 'r'); } function __destruct() { fclose($this->file); } } correctly opens the file with fopen and stores the handle in $this->file.

2. Step 2: Analyze destructor for closing file

   class FileHandler { private $file; function __construct($filename) { $this->file = fopen($filename, 'r'); } function __destruct() { fclose($this->file); } } correctly closes the file using fclose($this->file) in the destructor, ensuring cleanup.

3. Step 3: Check other options for errors

   class FileHandler { private $file; function __construct() { fclose($this->file); } function __destruct() { $this->file = fopen('file.txt', 'r'); } } reverses open/close actions. class FileHandler { function __construct($filename) { fclose($filename); } function __destruct() { fopen($filename, 'r'); } } misuses fclose and fopen with wrong variables. class FileHandler { private $file; function __construct($filename) { $this->file = fopen($filename, 'r'); } function __destruct() { echo 'File closed'; } } does not close the file, only prints a message.

4. Final Answer:

   class FileHandler { private $file; function __construct($filename) { $this->file = fopen($filename, 'r'); } function __destruct() { fclose($this->file); } } -> Option A

5. Quick Check:

   Open in __construct, close in __destruct = class FileHandler { private $file; function __construct($filename) { $this->file = fopen($filename, 'r'); } function __destruct() { fclose($this->file); } } [OK]

Hint: Open resource in constructor, close it in destructor [OK]

Common Mistakes:

• Closing file in constructor or opening in destructor
• Not storing file handle in a property
• Only printing message instead of closing resource