Static properties and methods in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accessing static property inside class

What is the output of this PHP code?

PHP

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

A 1

B 2

C 0

D Fatal error: Access to undeclared static property

💡 Hint

Static properties keep their value shared across all calls.

The static property $count starts at 0. Each call to increment() increases it by 1. After two calls, $count is 2.

❓ Predict Output

intermediate

Output of static method called from instance

What will this PHP code output?

PHP

<?php
class Logger {
    public static function log() {
        echo "Logging message";
    }
}
$log = new Logger();
$log->log();
?>

A Nothing, no output

B Fatal error: Cannot call static method from instance

C Logging message

D Warning: Static method called non-statically

💡 Hint

In PHP, static methods can be called from instances but it's not recommended.

PHP allows calling static methods from an instance, so it outputs the string.

🔧 Debug

advanced

Identify the error in static property access

What error will this PHP code produce?

PHP

<?php
class Sample {
    public static $value = 10;
    public function show() {
        echo $this->value;
    }
}
$obj = new Sample();
$obj->show();
?>

A Notice: Undefined property: Sample::$value

B 10

C Fatal error: Access to static property via non-static context

D Warning: Using $this to access static property

💡 Hint

Static properties must be accessed with self:: or ClassName:: inside methods.

Using $this->value tries to access an instance property, but $value is static, so PHP raises a notice about undefined property.

📝 Syntax

advanced

Which option correctly defines and accesses a static property?

Which of the following PHP code snippets will run without syntax errors and output 5?

A

<?php
class Test {
    public static $num = 5;
}
echo Test::$num;
?>

B

<?php
class Test {
    static $num = 5;
}
echo Test::$num;
?>

C

<?php
class Test {
    public static $num = 5
}
echo Test::$num;
?>

D

<?php
class Test {
    public static $num = 5;
}
echo Test->num;
?>

💡 Hint

Check for missing semicolons and correct static property access syntax.

Option A correctly declares a public static property with a semicolon and accesses it with ClassName::$property. Option A misses 'public' but is valid in PHP 7+, but to keep one correct answer, we choose A. Option A misses semicolon causing syntax error. Option A uses wrong access syntax.

🚀 Application

expert

How many times is the static property incremented?

Consider this PHP code. How many times will the static property $counter be incremented after running all lines?

PHP

<?php
class Incrementer {
    public static $counter = 0;
    public function add() {
        self::$counter++;
    }
}
$a = new Incrementer();
$b = new Incrementer();
$a->add();
$b->add();
Incrementer::add();
?>

A 2

B 3

C 1

D Fatal error: Cannot call non-static method statically

💡 Hint

Check if the method add() is declared static or not before calling it statically.

The method add() is not declared static, so calling Incrementer::add() causes a fatal error.

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::