Methods and $this keyword in PHP - Mini Project: Build & Apply

Methods and $this keyword

📖 Scenario: Imagine you are creating a simple program to manage a car's details. You want to store the car's brand and model, and then show this information using a method inside a class.

🎯 Goal: You will build a PHP class called Car with properties for brand and model. Then, you will add a method called displayInfo that uses the $this keyword to show the car's brand and model.

📋 What You'll Learn

Create a class named Car with two public properties: brand and model

Create an object of the Car class

Assign the values "Toyota" to brand and "Corolla" to model

Add a method called displayInfo inside the Car class that prints the brand and model using $this

Call the displayInfo method on the object and print the output

💡 Why This Matters

🌍 Real World

Classes and methods with <code>$this</code> are used to organize data and behavior in real-world PHP applications like websites and tools.

💼 Career

Understanding how to use classes and the <code>$this</code> keyword is essential for PHP developers building maintainable and reusable code.

1

Create the Car class with properties

Create a class called Car with two public properties: brand and model.

PHP

<?php

// Create class Car with public properties brand and model
// Your code here

Hint

Use class Car { } to create the class. Inside, declare public string $brand; and public string $model;.

2

Create a Car object and assign values

Create an object called $myCar from the Car class. Then assign "Toyota" to $myCar->brand and "Corolla" to $myCar->model.

PHP

<?php

class Car {
    public string $brand;
    public string $model;
}

// Create object $myCar and assign brand and model
// Your code here

Hint

Create the object with $myCar = new Car();. Assign values using $myCar->brand = "Toyota"; and $myCar->model = "Corolla";.

3

Add displayInfo method using $this

Inside the Car class, add a public method called displayInfo that prints the car's brand and model using $this->brand and $this->model.

PHP

brand = "Toyota";
$myCar->model = "Corolla";

Hint

Define the method with public function displayInfo() { }. Use echo "Brand: " . $this->brand . ", Model: " . $this->model; inside.

4

Call displayInfo method and print output

Call the displayInfo method on the $myCar object to print the car's brand and model.

PHP

brand . ", Model: " . $this->model . "\n";
    }
}

$myCar = new Car();
$myCar->brand = "Toyota";
$myCar->model = "Corolla";

// Call displayInfo method on $myCar
// Your code here

Hint

Call the method with $myCar->displayInfo(); to print the details.

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