Methods and $this keyword in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method using $this keyword

What is the output of this PHP code?

PHP

<?php
class Car {
    public $color = 'red';
    public function getColor() {
        return $this->color;
    }
}
$car = new Car();
echo $car->getColor();
?>

A Error: Undefined property

B Car

C null

D red

💡 Hint

Remember $this refers to the current object instance.

The method getColor() returns the $color property of the current object using $this->color. Since $color is set to 'red', the output is 'red'.

❓ Predict Output

intermediate

Effect of missing $this in method

What error or output does this PHP code produce?

PHP

<?php
class Person {
    public $name = 'Alice';
    public function sayName() {
        return name;
    }
}
$p = new Person();
echo $p->sayName();
?>

A Error: Undefined constant 'name'

B Alice

C null

D Empty string

💡 Hint

Check how properties are accessed inside methods.

Inside the method, name without $this-> is treated as a constant. Since no constant named 'name' exists, PHP throws an error.

🔧 Debug

advanced

Why does this method not update the property?

Consider this PHP code. Why does the setAge method not change the $age property of the object?

PHP

<?php
class User {
    public $age = 20;
    public function setAge($age) {
        $age = $age;
    }
}
$user = new User();
$user->setAge(30);
echo $user->age;
?>

A Because the method is static and cannot access instance properties.

B Because $age property is private and cannot be changed.

C Because the method assigns the parameter to itself, not to the property using $this.

D Because the property $age is not declared in the class.

💡 Hint

Look at how the assignment is done inside the method.

The method assigns the parameter $age to itself, which does nothing. To update the object's property, it should use $this->age = $age;.

📝 Syntax

advanced

Identify the syntax error in method using $this

Which option contains the correct syntax to return the $name property inside a method?

PHP

<?php
class Animal {
    public $name = 'Dog';
    public function getName() {
        // return statement here
    }
}
?>

A return $this->name;

B return this->$name;

C return $this.name;

D return $name;

💡 Hint

Remember the correct syntax to access properties with $this.

To access an object property inside a method, use $this->propertyName. Other options have syntax errors or incorrect variable usage.

🚀 Application

expert

Predict the output of chained method calls using $this

What is the output of this PHP code?

PHP

<?php
class Builder {
    private $text = '';
    public function addHello() {
        $this->text .= 'Hello ';
        return $this;
    }
    public function addWorld() {
        $this->text .= 'World!';
        return $this;
    }
    public function getText() {
        return $this->text;
    }
}
$b = new Builder();
echo $b->addHello()->addWorld()->getText();
?>

A Error: Cannot chain methods

B Hello World!

C World!

D Hello

💡 Hint

Check how methods return $this to allow chaining.

Each method appends text and returns $this, allowing chaining. The final getText() returns the full string 'Hello World!'.