Parent keyword behavior in PHP

Introduction

The parent keyword helps you use or change things from a parent class inside a child class.

When you want to call a method from the parent class inside a child class method.

When you want to access a property or method that is defined in the parent class.

When you want to extend or modify the behavior of a parent class method without rewriting it completely.

When you want to call the parent constructor from a child class constructor.

Syntax

PHP

parent::methodName();
parent::$propertyName;
parent::__construct();

parent:: is used to access methods or properties from the parent class.

You use it inside a child class to refer to the parent class.

Examples

This example shows how the child class Dog calls the parent class Animal method speak() using parent::speak() before adding its own message.

PHP

<?php
class Animal {
    public function speak() {
        echo "Animal sound\n";
    }
}

class Dog extends Animal {
    public function speak() {
        parent::speak();
        echo "Bark!\n";
    }
}

$dog = new Dog();
$dog->speak();

This example shows how the child class Car calls the parent constructor using parent::__construct() to keep the parent setup and add its own.

PHP

<?php
class Vehicle {
    public function __construct() {
        echo "Vehicle created\n";
    }
}

class Car extends Vehicle {
    public function __construct() {
        parent::__construct();
        echo "Car created\n";
    }
}

$car = new Car();

Sample Program

This program shows a Student class that uses parent::greet() to call the greet method from the Person parent class, adding its own message first.

PHP

<?php
class Person {
    public function greet() {
        echo "Hello from Person\n";
    }
}

class Student extends Person {
    public function greet() {
        echo "Student says: ";
        parent::greet();
    }
}

$student = new Student();
$student->greet();

Important Notes

You can only use parent:: inside a class that extends another class.

If the parent method or property does not exist, PHP will give an error.

Summary

parent lets child classes use or extend parent class methods or properties.

Use parent::methodName() to call a parent method inside a child method.

It helps avoid repeating code and keeps your program organized.

Practice

1. What does the parent keyword do in PHP classes?

easy

A. It renames the parent class.

B. It creates a new instance of the parent class.

C. It deletes the parent class methods from the child class.

D. It allows a child class to access methods or properties from its parent class.

Solution

1. Step 1: Understand the role of parent keyword

   The parent keyword in PHP is used inside a child class to refer to its parent class.

2. Step 2: Identify what parent allows

   It allows the child class to call or extend methods or properties defined in the parent class.

3. Final Answer:

   It allows a child class to access methods or properties from its parent class. -> Option D

4. Quick Check:

   parent accesses parent methods/properties [OK]

Hint: Remember: parent calls parent class features [OK]

Common Mistakes:

• Thinking parent creates new objects
• Confusing parent with $this
• Believing parent deletes methods

2. Which of the following is the correct syntax to call a parent class method named show inside a child class method?

easy

A. parent.show();

B. parent->show();

C. parent::show();

D. parent:show();

Solution

1. Step 1: Recall PHP syntax for calling parent methods

   In PHP, to call a parent class method inside a child, use the scope resolution operator :: with parent.

2. Step 2: Match the correct syntax

   The correct syntax is parent::methodName();, so for method show, it is parent::show();.

3. Final Answer:

   parent::show(); -> Option C

4. Quick Check:

   Use :: with parent to call methods [OK]

Hint: Use double colon (::) to call parent methods [OK]

Common Mistakes:

• Using arrow (->) instead of double colon (::)
• Using dot (.) operator which is for strings
• Using single colon (:) which is invalid syntax

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

class A {
  public function greet() {
    return "Hello from A";
  }
}

class B extends A {
  public function greet() {
    return parent::greet() . " and B";
  }
}

$b = new B();
echo $b->greet();

medium

A. Hello from A

B. Hello from A and B

C. Hello from B

D. Error: Cannot call parent method

Solution

1. Step 1: Understand method overriding and parent call

   Class B overrides greet() but calls parent::greet() which returns "Hello from A".

2. Step 2: Concatenate parent result with " and B"

   The child method returns the parent's string plus " and B", so the full string is "Hello from A and B".

3. Final Answer:

   Hello from A and B -> Option B

4. Quick Check:

   parent::greet() + " and B" = "Hello from A and B" [OK]

Hint: parent::method() returns parent's output, can concatenate [OK]

Common Mistakes:

• Ignoring parent:: call and expecting only child's string
• Thinking it causes an error
• Confusing output with only parent's or only child's string

4. Identify the error in this PHP code:

class ParentClass {
  public function sayHi() {
    echo "Hi from parent";
  }
}

class ChildClass extends ParentClass {
  public function sayHi() {
    parent.sayHi();
    echo " and child";
  }
}

$obj = new ChildClass();
$obj->sayHi();

medium

A. Using dot (.) instead of scope resolution (::) to call parent method

B. Missing parentheses after method name

C. Child class cannot override parent methods

D. Parent class method is private

Solution

1. Step 1: Check how parent method is called

   The code uses parent.sayHi(); which is invalid syntax in PHP.

2. Step 2: Correct syntax uses scope resolution operator

   It should be parent::sayHi(); to call the parent method inside child.

3. Final Answer:

   Using dot (.) instead of scope resolution (::) to call parent method -> Option A

4. Quick Check:

   Use parent::method(), not parent.method() [OK]

Hint: Use ::, not . to call parent methods [OK]

Common Mistakes:

• Using dot (.) operator for method calls
• Forgetting parentheses after method name
• Assuming private methods can be called by child

5. Given these classes, what will be the output?

class Base {
  protected function message() {
    return "Base message";
  }
}

class Derived extends Base {
  public function message() {
    return parent::message() . " extended";
  }
}

class MoreDerived extends Derived {
  public function message() {
    return parent::message() . " and more";
  }
}

$obj = new MoreDerived();
echo $obj->message();

hard

A. Base message extended and more

B. Base message and more

C. Error: Cannot access protected method

D. Base message extended

Solution

1. Step 1: Trace method calls through inheritance

   MoreDerived::message() calls parent::message() which is Derived::message().

2. Step 2: Derived::message() calls Base::message()

   Derived calls parent::message() which is Base::message() returning "Base message" and appends " extended".

3. Step 3: Combine all returned strings

   So Derived returns "Base message extended" and MoreDerived appends " and more" resulting in "Base message extended and more".

4. Final Answer:

   Base message extended and more -> Option A

5. Quick Check:

   Chained parent calls build full string [OK]

Hint: Each parent:: call adds to string stepwise [OK]

Common Mistakes:

• Expecting error due to protected method (allowed in child)
• Ignoring chained parent calls
• Assuming only base message prints