Parent keyword behavior in PHP - Step-by-Step Execution

Concept Flow - Parent keyword behavior

Define Parent Class with method

↓

Define Child Class extends Parent

↓

Override method in Child

↓

Call parent::method() inside Child method

↓

Execute Child method

↓

Parent method runs, then Child continues

Shows how a child class calls a method from its parent class using the parent keyword inside an overridden method.

Execution Sample

PHP

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

class ChildClass extends ParentClass {
  function greet() {
    parent::greet();
    echo "Hello from Child\n";
  }
}

$obj = new ChildClass();
$obj->greet();
?>

This code shows a child class calling its parent's greet method before adding its own message.

Execution Table

Step	Action	Evaluation	Output
1	Create ChildClass object	Object created
2	Call greet() on ChildClass object	ChildClass::greet() runs
3	Inside ChildClass::greet(), call parent::greet()	ParentClass::greet() runs	Hello from Parent
4	Continue ChildClass::greet() after parent call	Echo child message	Hello from Child
5	Method greet() ends	Return to caller

💡 Method greet() completes after printing both parent and child messages

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
$obj	null	ChildClass object	ChildClass object	ChildClass object	ChildClass object

Key Moments - 2 Insights

Why do we use parent::greet() inside the child method?

Using parent::greet() calls the original method from the parent class, allowing the child to add behavior without replacing the parent's code entirely, as shown in step 3 of the execution_table.

What happens if we omit parent::greet() in the child method?

If omitted, only the child's message prints because the parent's greet method is not called, so the output would miss "Hello from Parent", as seen by comparing step 3 and 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is printed at step 3?

A "Hello from Child"

B "Hello from Parent"

C Nothing is printed

D An error occurs

💡 Hint

Check the Output column at step 3 in the execution_table

At which step does the child class add its own message?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the Action and Output columns in the execution_table for when "Hello from Child" is printed

If we remove parent::greet() call, what changes in variable_tracker?

A $obj becomes null

B $obj changes to ParentClass object

C No change in $obj variable values

D $obj is undefined

💡 Hint

Variable $obj remains the same object regardless of method calls, see variable_tracker

Concept Snapshot

Parent keyword in PHP lets a child class call a method from its parent class.
Use parent::methodName() inside an overridden method.
This allows extending behavior without replacing it.
Without parent::, only child method runs.
Useful for code reuse and adding extra steps.

Full Transcript

This example shows how a child class in PHP can call a method from its parent class using the parent keyword. First, a ParentClass defines a greet method that prints a message. Then, ChildClass extends ParentClass and overrides greet. Inside ChildClass's greet, it calls parent::greet() to run the parent's method, then prints its own message. When we create a ChildClass object and call greet, the output shows the parent's message followed by the child's message. The execution table traces each step: creating the object, calling the method, calling the parent method, printing the child's message, and ending the method. The variable tracker shows the object stays the same throughout. Key moments clarify why parent:: is used and what happens if omitted. The quiz tests understanding of output at each step and variable state. This helps beginners see how inheritance and method overriding work with parent keyword in PHP.