Interface constants in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a constant named VERSION inside the interface.

PHP

<?php
interface AppInfo {
    const [1] = '1.0';
}
?>

Drag options to blanks, or click blank then click option'

ACONST_VERSION

BVERSION

CAppVersion

Dversion

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase names for constants.

Trying to use variables instead of constants.

The constant name inside an interface should be uppercase and descriptive. 'VERSION' is the correct constant name here.

2fill in blank

medium

Complete the code to access the constant MAX_USERS from the interface UserLimits.

PHP

<?php
interface UserLimits {
    const MAX_USERS = 100;
}

echo UserLimits::[1];
?>

Drag options to blanks, or click blank then click option'

AMAX_USERS

BMaxUsers

Cmax_users

DmaxUsers

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or camelCase names when accessing constants.

Trying to access constants as variables.

Constants are accessed with the interface name followed by :: and the constant name exactly as defined, which is 'MAX_USERS'.

3fill in blank

hard

Fix the error in the code by completing the blank to correctly access the constant.

PHP

<?php
interface Config {
    const TIMEOUT = 30;
}

class App implements Config {
    public function getTimeout() {
        return self::[1];
    }
}
?>

Drag options to blanks, or click blank then click option'

Atimeout

BConfig::TIMEOUT

CTIMEOUT

Dself::TIMEOUT

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to use the interface name with :: inside the class method.

Using lowercase constant names.

Inside the class implementing the interface, constants from the interface are accessed with self::CONSTANT_NAME. So 'TIMEOUT' is correct.

4fill in blank

hard

Fill both blanks to create a dictionary of constants from the interface with a condition.

PHP

<?php
interface StatusCodes {
    const OK = 200;
    const NOT_FOUND = 404;
    const ERROR = 500;
}

$codes = [
    'success' => StatusCodes::[1],
    'failure' => StatusCodes::[2]
];
?>

Drag options to blanks, or click blank then click option'

AOK

BNOT_FOUND

CERROR

DSUCCESS

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined constant names.

Mixing up the success and failure codes.

'success' should map to the OK code (200), and 'failure' should map to ERROR (500) from the interface constants.

5fill in blank

hard

Fill all three blanks to define an interface with constants and use them in a class method.

PHP

<?php
interface Settings {
    const [1] = 'dark';
    const [2] = 24;
}

class UserSettings implements Settings {
    public function getTheme() {
        return self::[3];
    }
}
?>

Drag options to blanks, or click blank then click option'

ATHEME

BFONT_SIZE

DFONT

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent constant names between interface and class.

Using lowercase or partial names.

The interface defines THEME and FONT_SIZE constants. The class method returns THEME using self::THEME.

Practice

1. What is the correct way to access a constant defined in a PHP interface named MyInterface with a constant VERSION?

easy

A. MyInterface->VERSION

B. $this->VERSION

C. self::VERSION

D. MyInterface::VERSION

Solution

1. Step 1: Understand interface constants access

   Constants in interfaces are accessed using the interface name followed by double colon (::) and the constant name.

2. Step 2: Apply correct syntax

   Using MyInterface::VERSION correctly accesses the constant defined in the interface.

3. Final Answer:

   MyInterface::VERSION -> Option D

4. Quick Check:

   Interface constants use InterfaceName::CONSTANT [OK]

Hint: Use InterfaceName::CONSTANT to access interface constants [OK]

Common Mistakes:

• Using $this->CONSTANT inside interface context
• Using self::CONSTANT which refers to class, not interface
• Using arrow operator (->) with interface name

2. Which of the following is the correct way to declare a constant inside a PHP interface?

easy

A. const MAX_SIZE = 100;

B. define('MAX_SIZE', 100);

C. public const MAX_SIZE = 100;

D. var MAX_SIZE = 100;

Solution

1. Step 1: Recall interface constant declaration rules

   In PHP interfaces, constants are declared using const keyword without visibility modifiers.

2. Step 2: Identify correct syntax

   const MAX_SIZE = 100; is the correct way. Using define() or visibility keywords is invalid in interfaces.

3. Final Answer:

   const MAX_SIZE = 100; -> Option A

4. Quick Check:

   Interface constants use const without visibility [OK]

Hint: Use const without public/private in interfaces [OK]

Common Mistakes:

• Using define() inside interface
• Adding public/private before const
• Using var keyword for constants

3. Given the interface and class below, what will be the output?

interface Status {
    const ACTIVE = 1;
    const INACTIVE = 0;
}

class User implements Status {
    public function getStatus() {
        return Status::ACTIVE;
    }
}

$user = new User();
echo $user->getStatus();

medium

A. ACTIVE

B. 0

C. 1

D. Error: Cannot access constant

Solution

1. Step 1: Understand interface constants usage

   The interface Status defines constants ACTIVE = 1 and INACTIVE = 0. The class User implements this interface.

2. Step 2: Trace method getStatus()

   The method returns Status::ACTIVE, which is the integer 1. The echo statement prints this value.

3. Final Answer:

   1 -> Option C

4. Quick Check:

   Interface constant value printed = 1 [OK]

Hint: Interface constants accessed as InterfaceName::CONSTANT return their value [OK]

Common Mistakes:

• Expecting constant name string instead of value
• Trying to access constant via $this
• Assuming constants are not accessible in implementing class

4. What is wrong with the following PHP code?

interface Config {
    public const TIMEOUT = 30;
}

medium

A. Interface constants must be assigned string values only

B. Constants in interfaces cannot have visibility modifiers

C. Constants must be declared as static in interfaces

D. Constants cannot be declared inside interfaces

Solution

1. Step 1: Review interface constant declaration rules

   In PHP, interface constants must be declared without visibility keywords like public, private, or protected.

2. Step 2: Identify the error in code

   The code uses public const TIMEOUT = 30;, which is invalid syntax for interface constants.

3. Final Answer:

   Constants in interfaces cannot have visibility modifiers -> Option B

4. Quick Check:

   No visibility allowed on interface constants [OK]

Hint: Do not add public/private before const in interfaces [OK]

Common Mistakes:

• Adding public or private before const in interface
• Thinking constants must be static in interfaces
• Assuming constants only accept strings

5. You want to define an interface Shape with constants CIRCLE = 1, SQUARE = 2, and TRIANGLE = 3. Then, create a class Circle implementing Shape that returns the shape type constant. Which code snippet correctly implements this?

hard

A. interface Shape {
const CIRCLE = 1;
const SQUARE = 2;
const TRIANGLE = 3;
}

class Circle implements Shape {
public function getType() {
return Shape::CIRCLE;
}
}

B. interface Shape {
public const CIRCLE = 1;
public const SQUARE = 2;
public const TRIANGLE = 3;
}

class Circle implements Shape {
public function getType() {
return $this->CIRCLE;
}
}

C. interface Shape {
const CIRCLE = 1;
const SQUARE = 2;
const TRIANGLE = 3;
}

class Circle implements Shape {
public function getType() {
return self::CIRCLE;
}
}

D. interface Shape {
const CIRCLE = 1;
const SQUARE = 2;
const TRIANGLE = 3;
}

class Circle implements Shape {
public function getType() {
return Shape->CIRCLE;
}
}

Solution

1. Step 1: Define interface constants correctly

   Constants in interface Shape are declared using const without visibility modifiers.

2. Step 2: Access constants correctly in implementing class

   Inside Circle, access the constant using Shape::CIRCLE. Using $this->CIRCLE or self::CIRCLE is incorrect because constants belong to the interface, not the class instance or class itself.

3. Final Answer:

   Option A code snippet correctly implements interface constants and access -> Option A

4. Quick Check:

   Interface constants accessed as InterfaceName::CONSTANT [OK]

Hint: Access interface constants with InterfaceName::CONSTANT, not $this or self [OK]

Common Mistakes:

• Adding public before const in interface
• Using $this->CONSTANT to access interface constant
• Using self::CONSTANT inside class for interface constant
• Using arrow operator (->) with interface name