Interface declaration and implementation in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an interface named Vehicle.

PHP

<?php
interface [1] {
    public function start();
}
?>

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

AStartable

BCar

CDrive

DVehicle

Attempts:

3 left

💡 Hint

Common Mistakes

Using a class name instead of an interface name.

Forgetting to use the keyword 'interface'.

The keyword interface is followed by the interface name. Here, the interface is named Vehicle.

2fill in blank

medium

Complete the code to implement the Vehicle interface in the Car class.

PHP

<?php
interface Vehicle {
    public function start();
}

class Car [1] Vehicle {
    public function start() {
        echo "Car started";
    }
}
?>

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

Auses

Bextends

Cimplements

Dinherits

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'extends' instead of 'implements' for interfaces.

Forgetting to implement all interface methods.

In PHP, a class implements an interface using the keyword implements.

3fill in blank

hard

Fix the error in the code by completing the method signature in the Car class.

PHP

<?php
interface Vehicle {
    public function start();
}

class Car implements Vehicle {
    public function [1] {
        echo "Car started";
    }
}
?>

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

Astart()

Bbegin()

CStart()

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting parentheses in the method declaration.

Using a different method name than declared in the interface.

The method name must exactly match the interface method including parentheses. So it should be start().

4fill in blank

hard

Fill both blanks to declare an interface and a class that implements it with a method.

PHP

<?php
interface [1] {
    public function [2]();
}

class Bike implements Vehicle {
    public function start() {
        echo "Bike started";
    }
}
?>

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

AVehicle

BCar

Cstart

Drun

Attempts:

3 left

💡 Hint

Common Mistakes

Using different method names in interface and class.

Mismatching interface and class names.

The interface is named Vehicle and the method declared is start(), matching the class implementation.

5fill in blank

hard

Fill all three blanks to create an interface with two methods and a class implementing both.

PHP

<?php
interface [1] {
    public function [2]();
    public function [3]();
}

class Plane implements Flyable {
    public function takeOff() {
        echo "Plane taking off";
    }
    public function land() {
        echo "Plane landing";
    }
}
?>

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

AFlyable

BtakeOff

Cland

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Not implementing all interface methods in the class.

Using method names in the interface that don't match the class.

The interface is named Flyable and declares two methods: takeOff() and land(), which the class Plane implements.

Practice

1. What is the main purpose of an interface in PHP?

easy

A. To execute code automatically when a program runs

B. To store variables and their values

C. To define method names without their code, ensuring classes implement them

D. To create objects directly

Solution

1. Step 1: Understand what an interface is

   An interface in PHP only declares method names without any code inside them.

2. Step 2: Understand the purpose of interfaces

   Interfaces ensure that any class implementing them must write the declared methods, helping organize code.

3. Final Answer:

   To define method names without their code, ensuring classes implement them -> Option C

4. Quick Check:

   Interface purpose = method declaration only [OK]

Hint: Interfaces declare methods only, no code inside [OK]

Common Mistakes:

• Thinking interfaces store variables
• Believing interfaces create objects
• Confusing interfaces with classes

2. Which of the following is the correct way to declare an interface named Vehicle in PHP?

easy

A. class Vehicle { public function start(); }

B. interface Vehicle { public function start(); }

C. interface Vehicle { function start() {} }

D. interface Vehicle { public function start() {} }

Solution

1. Step 1: Recall interface method declaration rules

   In interfaces, methods are declared without code blocks (no curly braces with code).

2. Step 2: Check each option

   'interface Vehicle { public function start(); }' declares interface and method without code, which is correct. Declarations with method bodies '{}' are wrong. Using 'class' instead of 'interface' is incorrect.

3. Final Answer:

   interface Vehicle { public function start(); } -> Option B

4. Quick Check:

   Interface methods have no body [OK]

Hint: Interface methods end with semicolon, no braces [OK]

Common Mistakes:

• Adding method bodies inside interfaces
• Using class keyword instead of interface
• Omitting semicolon after method declaration

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

interface Animal {
  public function sound();
}

class Dog implements Animal {
  public function sound() {
    return "Bark";
  }
}

$dog = new Dog();
echo $dog->sound();

medium

A. Bark

B. sound

C. Animal

D. Fatal error

Solution

1. Step 1: Understand interface and class implementation

   The interface Animal declares method sound(). Dog class implements Animal and defines sound() returning "Bark".

2. Step 2: Check the output of calling $dog->sound()

   Calling $dog->sound() returns "Bark" which is then echoed.

3. Final Answer:

   Bark -> Option A

4. Quick Check:

   Implemented method returns "Bark" [OK]

Hint: Implemented methods run normally, output their return [OK]

Common Mistakes:

• Expecting interface name as output
• Confusing method name with output
• Thinking code causes error without implementation

4. Identify the error in this PHP code:

interface Shape {
  public function area();
}

class Circle implements Shape {
  public function area() {
    return 3.14 * 5 * 5;
  }

  public function perimeter() {
    return 2 * 3.14 * 5;
  }
}

$circle = new Circle();
echo $circle->area();

medium

A. No error, code runs and outputs area

B. Missing implementation of perimeter() in interface

C. Interface method area() has no body, causing error

D. Class Circle must implement all interface methods

Solution

1. Step 1: Check interface and class methods

   Interface Shape declares area(). Circle implements area() correctly and adds extra method perimeter() which is allowed.

2. Step 2: Verify if code runs without error

   Since all interface methods are implemented, extra methods are allowed. Code outputs area value.

3. Final Answer:

   No error, code runs and outputs area -> Option A

4. Quick Check:

   Extra methods allowed, interface methods implemented [OK]

Hint: Extra methods in class are allowed beyond interface [OK]

Common Mistakes:

• Thinking extra methods must be in interface
• Confusing method body rules in interface
• Assuming missing interface methods cause error here

5. You have two interfaces:

interface Printer {
  public function printDocument();
}

interface Scanner {
  public function scanDocument();
}

How can you create a class AllInOne that implements both interfaces and provides method bodies?

hard

A. class AllInOne implements Scanner {
public function printDocument() { return "Printing..."; }
public function scanDocument() { return "Scanning..."; }
}

B. class AllInOne implements Printer {
public function printDocument() { return "Printing..."; }
public function scanDocument() { return "Scanning..."; }
}

C. class AllInOne {
public function printDocument() { return "Printing..."; }
public function scanDocument() { return "Scanning..."; }
}

D. class AllInOne implements Printer, Scanner {
public function printDocument() { return "Printing..."; }
public function scanDocument() { return "Scanning..."; }
}

Solution

1. Step 1: Understand multiple interface implementation

   PHP allows a class to implement multiple interfaces by listing them separated by commas.

2. Step 2: Check which option correctly implements both interfaces

   class AllInOne implements Printer, Scanner { public function printDocument() { return "Printing..."; } public function scanDocument() { return "Scanning..."; } } implements both Printer and Scanner and defines both required methods. Others miss one interface or do not implement any.

3. Final Answer:

   class AllInOne implements Printer, Scanner { public function printDocument() { return "Printing..."; } public function scanDocument() { return "Scanning..."; } } -> Option D

4. Quick Check:

   Multiple interfaces implemented with commas [OK]

Hint: Use commas to implement multiple interfaces in one class [OK]

Common Mistakes:

• Implementing only one interface when multiple required
• Forgetting to implement all interface methods
• Not using commas to separate interfaces