Instanceof operator in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the instanceof operator do in PHP?

It checks if an object is an instance of a specific class or implements a specific interface.

beginner

How do you use instanceof to check if $obj is an instance of class Car?

Use <code>$obj instanceof Car</code>. It returns <code>true</code> if <code>$obj</code> is a Car or subclass of Car, otherwise <code>false</code>.

intermediate

Can instanceof check if an object implements an interface?

Yes. It returns true if the object implements the interface, otherwise false.

beginner

What will instanceof return if the variable is not an object?

It returns false because instanceof only works with objects.

intermediate

Explain why instanceof is useful in PHP programming.

It helps to safely check an object's type before calling methods or accessing properties, preventing errors.

What does $obj instanceof ClassName return if $obj is an instance of a subclass of ClassName?

A false

B true

C null

D Throws an error

instanceof returns true if the object is an instance of the class or any subclass.

Which of the following is true about instanceof in PHP?

A It can check if an object implements an interface.

B It can check if a variable is an integer.

C It can check if a string contains a class name.

D It can create a new instance of a class.

instanceof checks object type or interface implementation, not primitive types or strings.

What will instanceof return if the variable is null?

A false

B Throws an error

C null

D true

null is not an object, so instanceof returns false.

If $obj instanceof InterfaceName returns true, what does it mean?

A $obj is a subclass of InterfaceName.

B $obj is a string containing InterfaceName.

C $obj is an instance of a class that implements InterfaceName.

D $obj is an array.

instanceof confirms the object implements the interface.

Which of these is a correct use of instanceof?

A if (MyClass instanceof $obj) { /* code */ }

B if (instanceof $obj MyClass) { /* code */ }

C if ($obj instanceof 'MyClass') { /* code */ }

D if ($obj instanceof MyClass) { /* code */ }

The correct syntax is $obj instanceof ClassName.

Describe how the instanceof operator works in PHP and give an example.

Think about checking an object's type before using it.

Explain why using instanceof can help prevent errors in PHP programs.

Consider what happens if you call a method on a variable that is not an object.