Methods and $this keyword in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call the method inside the class using $this.

PHP

<?php
class Car {
    public function start() {
        echo "Car started";
    }
    public function run() {
        $this->[1]();
    }
}
$car = new Car();
$car->run();
?>

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

Astop

Brun

Cstart

Ddrive

Attempts:

3 left

💡 Hint

Common Mistakes

Using the method name without $this->

Calling a method that does not exist

Inside a class, to call another method, you use $this->methodName(). Here, $this->start() calls the start method.

2fill in blank

medium

Complete the code to access the property inside the method using $this.

PHP

<?php
class Person {
    public $name = "Alice";
    public function greet() {
        echo "Hello, " . $this->[1];
    }
}
$person = new Person();
$person->greet();
?>

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

Aname

Bhello

Cgreet

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access property without $this->

Using a wrong property name

Inside the method, $this->name accesses the property 'name' of the current object.

3fill in blank

hard

Fix the error in the method to correctly return the object's property using $this.

PHP

<?php
class Book {
    public $title = "PHP Basics";
    public function getTitle() {
        return [1]->title;
    }
}
$book = new Book();
echo $book->getTitle();
?>

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

Athis

B$this

C$self

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'this' without $ sign

Using 'self' which refers to the class, not the object instance

In PHP, $this refers to the current object inside methods. So, return $this->title; is correct.

4fill in blank

hard

Fill both blanks to create a method that sets the object's property using $this.

PHP

<?php
class Laptop {
    public $brand;
    public function setBrand([1]) {
        $this->[2] = $brand;
    }
}
$laptop = new Laptop();
$laptop->setBrand("Dell");
echo $laptop->brand;
?>

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

Astring $brand

Bbrand

Cmodel

Dprice

Attempts:

3 left

💡 Hint

Common Mistakes

Not using a parameter in the method

Assigning to a wrong property name

The method parameter should be 'string $brand' to accept a string argument. Inside the method, $this->brand sets the object's property.

5fill in blank

hard

Fill all three blanks to create a method that updates and returns the object's property using $this.

PHP

<?php
class Phone {
    public $color = "Black";
    public function changeColor([1]) {
        $this->[2] = $newColor;
        return $this->[3];
    }
}
$phone = new Phone();
echo $phone->changeColor("Red");
?>

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

Astring $newColor

Bcolor

DnewColor

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter name

Returning a variable instead of the property

The method parameter is 'string $newColor'. Inside the method, $this->color is updated and returned.

Practice

1. What does the $this keyword represent inside a PHP class method?

easy

A. A global variable

B. A static variable

C. The current object instance

D. The class name

Solution

1. Step 1: Understand the role of $this in PHP classes

   $this is used inside class methods to refer to the current object instance that called the method.

2. Step 2: Differentiate from other options

   It is not a static or global variable, nor does it represent the class name itself.

3. Final Answer:

   The current object instance -> Option C

4. Quick Check:

   $this = current object instance [OK]

Hint: Remember: $this always means 'this object' [OK]

Common Mistakes:

• Confusing $this with static variables
• Thinking $this is the class name
• Assuming $this is a global variable

2. Which of the following is the correct way to call a method named greet inside a PHP class using $this?

easy

A. this->greet();

B. self->greet();

C. $this.greet();

D. $this->greet();

Solution

1. Step 1: Recall PHP method call syntax inside classes

   Methods are called on objects using the arrow operator -> with $this representing the current object.

2. Step 2: Check each option

   $this->greet(); is the correct syntax. The other options use invalid syntax.

3. Final Answer:

   $this->greet(); -> Option D

4. Quick Check:

   Method call syntax = $this->method(); [OK]

Hint: Use $this->methodName(); to call methods inside class [OK]

Common Mistakes:

• Using dot (.) instead of arrow (->) operator
• Omitting the dollar sign in $this
• Using self without scope resolution operator

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

class Person {
  public $name = 'Alice';
  public function sayName() {
    return 'Name: ' . $this->name;
  }
}
$p = new Person();
echo $p->sayName();

medium

A. Name: Alice

B. Name: $name

C. Name:

D. Error: Undefined property

Solution

1. Step 1: Understand property access with $this

   The method sayName() returns the string 'Name: ' concatenated with the object's name property accessed via $this->name.

2. Step 2: Check the property value and output

   The property name is set to 'Alice', so the output will be 'Name: Alice'.

3. Final Answer:

   Name: Alice -> Option A

4. Quick Check:

   Property accessed via $this = 'Alice' [OK]

Hint: Remember: $this->property accesses current object's data [OK]

Common Mistakes:

• Forgetting to use $this to access properties
• Expecting literal string output without variable substitution
• Confusing property name with string '$name'

4. Identify the error in this PHP class method:

class Car {
  public $model = 'Tesla';
  public function getModel() {
    return $model;
  }
}

medium

A. Missing $this when accessing $model

B. Method name should be GetModel with capital G

C. Property $model must be private

D. Return statement should be return $this->getModel;

Solution

1. Step 1: Check property access inside method

   Inside class methods, properties must be accessed with $this->propertyName. Here, $model is used without $this->.

2. Step 2: Validate other options

   Method names are case-insensitive in PHP, property visibility is not an error here, and the suggested return $this->getModel; is incorrect.

3. Final Answer:

   Missing $this when accessing $model -> Option A

4. Quick Check:

   Use $this->property to access properties [OK]

Hint: Always use $this-> to access object properties inside methods [OK]

Common Mistakes:

• Accessing properties without $this->
• Confusing method name case sensitivity
• Misunderstanding property visibility rules

5. Given the class below, what will be the output?

class Counter {
  private $count = 0;
  public function increment() {
    $this->count++;
  }
  public function getCount() {
    return $this->count;
  }
}
$c = new Counter();
$c->increment();
$c->increment();
echo $c->getCount();

hard

A. Error: Cannot access private property

B. 2

C. 1

D. 0

Solution

1. Step 1: Understand property increment inside the class

   The increment() method increases the private $count property by 1 each time it is called.

2. Step 2: Trace method calls and final output

   Calling increment() twice increases $count from 0 to 2. Then getCount() returns 2.

3. Final Answer:

   2 -> Option B

4. Quick Check:

   Two increments = count 2 [OK]

Hint: Private properties accessed via $this inside class work fine [OK]

Common Mistakes:

• Assuming private properties can't be accessed inside class methods
• Forgetting that increment operator changes value
• Expecting output before increments