Method overriding in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method overriding with parent call

What is the output of this PHP code when run?

PHP

<?php
class Animal {
    public function sound() {
        return "Some sound";
    }
}

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

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

A Error: Cannot override method

B Some sound

C Bark

D No output

💡 Hint

Look at which class's method is called when you create a Dog object.

The Dog class overrides the sound method of Animal. When calling $dog->sound(), the overridden method in Dog runs, returning "Bark".

❓ Predict Output

intermediate

Output when calling parent method inside overridden method

What will this PHP code output?

PHP

<?php
class Vehicle {
    public function start() {
        return "Vehicle started";
    }
}

class Car extends Vehicle {
    public function start() {
        return parent::start() . " and Car ready";
    }
}

$car = new Car();
echo $car->start();
?>

A Fatal error: Cannot access parent method

B Car ready

C Vehicle started

D Vehicle started and Car ready

💡 Hint

The overridden method calls the parent method and adds extra text.

The Car class overrides start() but calls parent::start() to get the base message, then adds " and Car ready". So the output is combined.

🔧 Debug

advanced

Identify the error in method overriding

What error will this PHP code produce when run?

PHP

<?php
class Base {
    private function show() {
        echo "Base show";
    }
}

class Child extends Base {
    public function show() {
        echo "Child show";
    }
}

$obj = new Child();
$obj->show();
?>

A Outputs: Child show

B Outputs: Base show

C Fatal error: Cannot override private method Base::show()

D Fatal error: Call to private method Base::show() from Child

💡 Hint

Private methods are not visible to child classes, so Child defines its own method.

The show method in Base is private, so Child does not override it but defines a new method. Calling $obj->show() calls Child's method, outputting "Child show".

📝 Syntax

advanced

Which option causes a syntax error in method overriding?

Which of the following PHP code snippets will cause a syntax error?

A

<?php
class A {
    public function test() {}
}
class B extends A {
    public function test() {
        parent::test();
        echo "Hi";
    }
}
?>

B

<?php
class A {
    public function test() {}
}
class B extends A {
    public function test() 
        echo "Hi";
    }
}
?>

C

<?php
class A {
    public function test() {}
}
class B extends A {
    public function test() {
        echo "Hello";
    }
}
?>

D

<?php
class A {
    public function test() {}
}
class B extends A {
    public function test() {
        return "Hi";
    }
}
?>

💡 Hint

Check for missing braces or incorrect function syntax.

Option B is missing the opening brace { after the method declaration, causing a syntax error.

🚀 Application

expert

Determine the final output with multiple overrides and parent calls

What is the output of this PHP code?

PHP

<?php
class A {
    public function message() {
        return "A";
    }
}

class B extends A {
    public function message() {
        return "B" . parent::message();
    }
}

class C extends B {
    public function message() {
        return "C" . parent::message();
    }
}

$obj = new C();
echo $obj->message();
?>

A CBA

B Error: Cannot call parent method

C CAB

D ABC

💡 Hint

Each class adds its letter and calls the parent's message method.

Class C calls B::message(), which calls A::message(). The output concatenates "C" + "B" + "A" = "CBA".

Practice

1. What does method overriding allow a child class to do in PHP?

easy

A. Change the behavior of a method inherited from the parent class

B. Create a new method with a different name

C. Prevent the parent class from being instantiated

D. Automatically call all parent methods

Solution

1. Step 1: Understand method overriding concept

   Method overriding means a child class uses the same method name as the parent to change its behavior.

2. Step 2: Identify what overriding does

   It replaces or modifies the parent's method behavior in the child class.

3. Final Answer:

   Change the behavior of a method inherited from the parent class -> Option A

4. Quick Check:

   Method overriding = change parent method behavior [OK]

Hint: Overriding means same method name, new behavior [OK]

Common Mistakes:

• Thinking overriding creates new methods with different names
• Confusing overriding with inheritance itself
• Believing overriding prevents parent instantiation

2. Which of the following is the correct syntax to override a method named greet in a child class in PHP?

easy

A. function greetChild() { /* new code */ }

B. function greet() { /* new code */ }

C. override function greet() { /* new code */ }

D. parent::greet() { /* new code */ }

Solution

1. Step 1: Recall method overriding syntax

   To override, define a method with the same name in the child class.

2. Step 2: Check options for correct syntax

   Only function greet() { /* new code */ } defines function greet() correctly without extra keywords.

3. Final Answer:

   function greet() { /* new code */ } -> Option B

4. Quick Check:

   Same method name in child = override [OK]

Hint: Use same method name in child class to override [OK]

Common Mistakes:

• Adding 'override' keyword which PHP does not use
• Changing method name to something else
• Trying to call parent method syntax incorrectly

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

class ParentClass {
  function sayHello() {
    echo "Hello from Parent";
  }
}
class ChildClass extends ParentClass {
  function sayHello() {
    echo "Hello from Child";
  }
}
$obj = new ChildClass();
$obj->sayHello();

medium

A. Hello from ParentChild

B. Hello from Parent

C. Hello from Child

D. Error: Method not found

Solution

1. Step 1: Identify method overriding in ChildClass

   ChildClass defines sayHello() which overrides ParentClass method.

2. Step 2: Check which method is called

   Creating ChildClass object calls ChildClass's sayHello(), printing "Hello from Child".

3. Final Answer:

   Hello from Child -> Option C

4. Quick Check:

   Child method overrides parent = "Hello from Child" [OK]

Hint: Child method runs if overridden, not parent [OK]

Common Mistakes:

• Expecting parent method output instead of child
• Thinking both outputs print together
• Assuming error due to method name clash

4. Find the error in this PHP code that tries to override a method:

class Base {
  function show() {
    echo "Base";
  }
}
class Derived extends Base {
  function show() {
    parent.show();
    echo " Derived";
  }
}
$obj = new Derived();
$obj->show();

medium

A. Class Derived must declare show() as public

B. Cannot override methods in PHP

C. Missing return statement in show()

D. Incorrect syntax to call parent method; should use parent::show()

Solution

1. Step 1: Identify how parent method is called

   The code uses parent.show() which is invalid syntax in PHP.

2. Step 2: Correct syntax for calling parent method

   PHP requires parent::show() to call the parent's method inside child.

3. Final Answer:

   Incorrect syntax to call parent method; should use parent::show() -> Option D

4. Quick Check:

   Call parent method with parent::method() [OK]

Hint: Use parent::method() to call parent method inside child [OK]

Common Mistakes:

• Using dot (.) instead of :: to call parent method
• Thinking overriding is not allowed
• Forgetting to call parent method when needed

5. Given these classes, what will be the output?

class Animal {
  function sound() {
    echo "Some sound";
  }
}
class Dog extends Animal {
  function sound() {
    parent::sound();
    echo " and Bark";
  }
}
class Puppy extends Dog {
  function sound() {
    echo "Yip";
  }
}
$pet = new Puppy();
$pet->sound();

hard

A. Yip

B. Some sound and Bark and Yip

C. Some sound and Bark

D. Error: Cannot override multiple times

Solution

1. Step 1: Trace method calls for Puppy object

   Puppy overrides sound() and only echoes "Yip" without calling parent.

2. Step 2: Understand overriding chain

   Since Puppy method does not call parent::sound(), Dog and Animal methods are not executed.

3. Final Answer:

   Yip -> Option A

4. Quick Check:

   Child override without parent call = only child output [OK]

Hint: If child method skips parent call, only child output shows [OK]

Common Mistakes:

• Assuming all parent methods run automatically
• Expecting combined outputs without explicit parent calls
• Thinking multiple overrides cause errors