Static properties and methods in PHP - Mini Project: Build & Apply

Using Static Properties and Methods in PHP

📖 Scenario: Imagine you are creating a simple system to count how many users have registered on a website. You want to keep track of the total number of users without creating a new counter for each user.

🎯 Goal: Build a PHP class with a static property to count users and a static method to display the total count.

📋 What You'll Learn

Create a class called User.

Add a static property called count initialized to 0.

Add a static method called incrementCount that increases count by 1.

Add a static method called getCount that returns the current value of count.

Call the static methods to simulate user registrations and display the total count.

💡 Why This Matters

🌍 Real World

Static properties and methods are used to keep track of information that applies to all objects of a class, like counting users, managing configuration, or caching data.

💼 Career

Understanding static members is important for backend development, especially when working with shared resources or global counters in PHP applications.

1

Create the User class with a static property

Create a class called User with a static property named count set to 0.

PHP

<?php
class User {
    // Your code here
}

Hint

Use public static to declare the static property inside the class.

2

Add static methods to update and get the count

Inside the User class, add a static method called incrementCount that increases count by 1, and another static method called getCount that returns the value of count.

PHP

<?php
class User {
    public static int $count = 0;

    // Your code here
}

Hint

Use self::$count to access the static property inside static methods.

3

Simulate user registrations by calling the static method

Outside the User class, call the static method incrementCount three times to simulate three user registrations.

PHP

<?php
class User {
    public static int $count = 0;

    public static function incrementCount(): void {
        self::$count++;
    }

    public static function getCount(): int {
        return self::$count;
    }
}

// Your code here

Hint

Call the static method using User::incrementCount();.

4

Display the total number of users

Use print to display the text 'Total users: ' followed by the result of calling the static method getCount from the User class.

PHP

<?php
class User {
    public static int $count = 0;

    public static function incrementCount(): void {
        self::$count++;
    }

    public static function getCount(): int {
        return self::$count;
    }
}

User::incrementCount();
User::incrementCount();
User::incrementCount();

// Your code here

Hint

Use print("Total users: " . User::getCount()); to show the count.

Practice

1. Which statement about static properties in PHP is true?
class Example { public static $count = 0; }

easy

A. Static properties belong to the class itself, not to any object instance.

B. Static properties can only be accessed through object instances.

C. Static properties cannot hold values.

D. Static properties are private by default.

Solution

1. Step 1: Understand static property ownership

   Static properties belong to the class, not to individual objects.

2. Step 2: Check access rules

   Static properties are accessed using the class name, not object instances.

3. Final Answer:

   Static properties belong to the class itself, not to any object instance. -> Option A

4. Quick Check:

   Static property = class-level data [OK]

Hint: Static means class-level, not per object [OK]

Common Mistakes:

• Thinking static properties belong to objects
• Trying to access static properties via objects
• Assuming static properties can't hold values

2. Which of the following is the correct syntax to call a static method show() of class Test?

easy

A. $obj->show();

B. $obj::show();

C. Test->show();

D. Test::show();

Solution

1. Step 1: Recall static method call syntax

   Static methods are called using the class name and double colon (::).

2. Step 2: Check each option

   Test::show(); uses Test::show(); which is correct syntax.

3. Final Answer:

   Test::show(); -> Option D

4. Quick Check:

   Static method call = ClassName::method() [OK]

Hint: Use ClassName::method() to call static methods [OK]

Common Mistakes:

• Using object arrow (->) to call static methods
• Using object variable with :: operator incorrectly
• Using class arrow (->) which is invalid

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

class Counter {
    public static $count = 0;
    public static function increment() {
        self::$count++;
    }
}
Counter::increment();
Counter::increment();
echo Counter::$count;

medium

A. 1

B. 2

C. 0

D. Error

Solution

1. Step 1: Understand static property and method behavior

   Static property $count starts at 0 and is shared by the class.

2. Step 2: Trace method calls

   Each call to increment() increases $count by 1. Two calls increase it to 2.

3. Final Answer:

   2 -> Option B

4. Quick Check:

   2 increments = 2 count [OK]

Hint: Static property keeps value across calls [OK]

Common Mistakes:

• Thinking static resets per call
• Confusing self:: with $this->
• Expecting error due to static usage

4. Identify the error in this PHP code snippet:

class Sample {
    public static $value = 10;
    public function show() {
        echo self->$value;
    }
}
$object = new Sample();
$object->show();

medium

A. Cannot use echo inside class methods.

B. Static property cannot be accessed inside non-static methods.

C. Using self::$value instead of self->$value inside the method.

D. Missing static keyword before method declaration.

Solution

1. Step 1: Check static property access syntax

   Static properties must be accessed with self::$propertyName, not self->$propertyName.

2. Step 2: Verify method and property usage

   The method is non-static but can access static properties using self:: syntax.

3. Final Answer:

   Using self::$value instead of self->$value inside the method. -> Option C

4. Quick Check:

   Static property access = self::$property [OK]

Hint: Use :: for static properties, not -> or $ [OK]

Common Mistakes:

• Using $ before property name with self::
• Trying to access static property with $this->
• Confusing static and non-static method rules

5. You want to count how many objects of class User have been created using a static property. Which code correctly implements this?

class User {
    public static $count = 0;
    public function __construct() {
        // What goes here?
    }
}

hard

A. self::$count++;

B. $this->count++;

C. User->count++;

D. static->count++;

Solution

1. Step 1: Understand static property increment in constructor

   Each time an object is created, the constructor runs and should increase the static count.

2. Step 2: Use correct syntax to increment static property

   Use self::$count++; inside the constructor to increment the static property.

3. Final Answer:

   self::$count++; -> Option A

4. Quick Check:

   Increment static with self::$property++ [OK]

Hint: Use self::$property to access static inside class [OK]

Common Mistakes:

• Using $this->count++ which accesses instance property
• Using arrow (->) with class name or static keyword
• Trying to increment static property without self::