Methods and $this keyword in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a method in PHP classes?

A method is a function defined inside a class that describes behaviors or actions objects of that class can perform.

beginner

What does the <code>$this</code> keyword represent inside a PHP class method?

$this refers to the current object instance that is calling the method. It allows access to the object's properties and other methods.

intermediate

How do you call a method from inside another method in the same PHP class?

Use $this->methodName() to call another method of the same object.

intermediate

Why can't you use $this in static methods?

Static methods belong to the class itself, not to any object instance, so <code>$this</code> (which refers to an object) is not available.

beginner

Example: What will $this->name access inside a method?

It accesses the name property of the current object instance.

Inside a PHP class method, what does $this refer to?

A The current object instance

B The class itself

C A global variable

D A static method

$this always refers to the current object instance inside non-static methods.

How do you call a method named greet from another method in the same PHP class?

A greet()

B self::greet()

C $this->greet()

D ClassName::greet()

Use $this->greet() to call a method on the current object.

Can you use $this inside a static method?

A Only if the method is private

B Yes, always

C Only if the method is public

D No, because static methods do not belong to an object instance

$this is not available in static methods because they belong to the class, not an object.

What will $this->property access inside a method?

A A global variable

B The property of the current object

C A static property

D A local variable

$this->property accesses the property of the current object instance.

Which keyword is used to refer to the current object inside a PHP class?

A $this

B self

C parent

D static

$this is the keyword for the current object instance.

Explain what $this means in PHP and how it is used inside class methods.

Think about how an object refers to itself.

Describe how to call one method from another method inside the same PHP class.

Remember how you access properties with $this->property.

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