PHP OOP Class Constants
🧊 PHP OOP – Class Constants
You define it using the keyword:
🔷 1. Basic Class Constant Example
✔ Output:
Hello World
Note: You access constants using :: (Scope Resolution Operator)
No need to create an object.
🔥 2. Constants Inside Object
Even if constants belong to class, you can access using object:
But preferred is:
🟩 3. Multiple Constants in a Class
🟦 4. Constants Are Always Public
Class constants:
✔ Cannot be private
✔ Cannot be protected
✔ Visibility modifiers are NOT allowed
This is valid in PHP 7.1+:
But older PHP versions only allow:
🟥 5. Constants vs Variables
| Feature | Constant | Property (Variable) |
|---|---|---|
| Defined using | const |
public $name |
| Change value | ❌ No | ✔ Yes |
| Access using | ClassName::CONST |
$obj->property |
| Memory | Fixed | Depends |
| Object required | ❌ No | ✔ Yes |
🟧 6. Constants with Inheritance
A child class can access parent constants.
🟨 7. Overriding Constants
A child class can redefine (override) constants.
🟪 8. Use Class Name Dynamically
🟫 9. Practical Use Case of Class Constants
Example: Application configuration
Example: Product Types
🎯 Summary (Easy to Remember)
| Feature | Meaning |
|---|---|
const |
Create constant inside class |
| Access | ClassName::CONST_NAME |
| No object needed | ✔ |
| Cannot change value | ✔ |
| Used for fixed data | ✔ |
