Method overriding in PHP - Time & Space Complexity

Time Complexity: Method overriding

O(1)

Understanding Time Complexity

We want to understand how the time it takes to run a program changes when we use method overriding in PHP.

Specifically, does replacing a method in a child class affect how long the program runs as it gets bigger?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

class Animal {
    public function speak() {
        echo "Animal sound\n";
    }
}

class Dog extends Animal {
    public function speak() {
        echo "Bark\n";
    }
}

$dog = new Dog();
$dog->speak();
    

This code shows a child class overriding a method from its parent class and then calling it.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Calling the overridden method speak() once.
• How many times: Exactly one time in this example.

How Execution Grows With Input

Since the method is called only once, the time to run does not grow with input size.

Input Size (n)	Approx. Operations
10	1 method call
100	1 method call
1000	1 method call

Pattern observation: The number of operations stays the same no matter how big the input is.

Final Time Complexity

Time Complexity: O(1)

This means the time to run the method does not change as the input size grows.

Common Mistake

[X] Wrong: "Overriding a method makes the program slower as input grows because it adds extra steps."

[OK] Correct: Overriding just replaces the method code; it does not add loops or repeated work by itself.

Interview Connect

Understanding how method overriding affects performance helps you explain your code design clearly and shows you know how programs run under the hood.

Self-Check

"What if the overridden method contained a loop that runs n times? How would the time complexity change?"