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PHPprogramming~10 mins

Final classes and methods in PHP - Step-by-Step Execution

Choose your learning style9 modes available
Concept Flow - Final classes and methods
Define final class
Try to extend final class?
YesError: Cannot extend final class
No
Define class with final method
Try to override final method?
YesError: Cannot override final method
No
Use class and methods normally
This flow shows how final classes cannot be extended and final methods cannot be overridden, causing errors if attempted.
Execution Sample
PHP
<?php
final class Base {
  public function greet() {
    return "Hello";
  }
}

class Child extends Base {}
?>
This code tries to extend a final class, which causes an error.
Execution Table
StepActionCode LineResultError
1Define final class Basefinal class Base {...}Class Base createdNone
2Define class Child extending Baseclass Child extends Base {}Attempt to create ChildFatal error: Cannot extend final class Base
3Execution stops--Error stops script
💡 Error occurs because Child tries to extend final class Base
Variable Tracker
VariableStartAfter Step 1After Step 2Final
Class Baseundefineddefineddefineddefined
Class Childundefinedundefinederror (not defined)error (not defined)
Key Moments - 2 Insights
Why does PHP give an error when trying to extend a final class?
Because final classes cannot be extended. As shown in execution_table step 2, PHP stops with a fatal error when Child tries to extend Base.
Can a final method be overridden in a child class?
No. If a method is declared final, any attempt to override it in a subclass causes an error, similar to final classes but at method level.
Visual Quiz - 3 Questions
Test your understanding
Look at the execution table, what happens at step 2?
AChild class is created successfully
BNo error, program continues
CFatal error because Child tries to extend final class Base
DBase class is deleted
💡 Hint
Check execution_table row with Step 2 for error details
According to variable_tracker, what is the state of Class Child after step 2?
ADefined and usable
BUndefined due to error
COverridden Base class
DFinal class
💡 Hint
Look at variable_tracker row for Class Child after Step 2
If the final keyword is removed from class Base, what changes in the execution table?
AStep 2 error disappears, Child class is created
BStep 1 causes error
CStep 3 error appears
DNo change, error remains
💡 Hint
Final keyword prevents extension; removing it allows Child creation
Concept Snapshot
final class ClassName {
  // class body
}

final methods prevent overriding:
class A {
  final function f() {}
}

- final class: cannot be extended
- final method: cannot be overridden
- Trying to do so causes fatal error
Full Transcript
In PHP, a final class cannot be extended by any other class. If you try to create a subclass from a final class, PHP stops with a fatal error. Similarly, a method declared as final inside a class cannot be overridden by subclasses. This example shows a final class Base and an attempt to extend it with Child, which causes an error. Variables track that Base is defined but Child is not created due to the error. Remember, final keyword protects classes or methods from being changed by inheritance.