Difference Between Compile Time and Run Time Polymorphism in Java

What is Run Time Polymorphism?

Run-time polymorphism, or dynamic polymorphism, is all about method overriding. Unlike its compile-time counterpart, decisions about which method to invoke are made at runtime. This polymorphism is closely tied to inheritance & the use of base class references to point to subclass objects.

To illustrate, let's consider a basic example involving a superclass Animal and its subclasses Dog & Cat. Each subclass has its own implementation of the makeSound method.

• Java

Java

class Animal {
    void makeSound() {
        System.out.println("Some generic animal sound");
    }
}

class Dog extends Animal {
    void makeSound() {
        System.out.println("Bark");
    }
}

class Cat extends Animal {
    void makeSound() {
        System.out.println("Meow");
    }
}

public class Main {
    public static void main(String[] args) {
        Animal myAnimal = new Animal();
        Animal myDog = new Dog();
        Animal myCat = new Cat();

        myAnimal.makeSound(); // Outputs "Some generic animal sound"
        myDog.makeSound();    // Outputs "Bark"
        myCat.makeSound();    // Outputs "Meow"
    }
}

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Output

This code is an example of run-time polymorphism where the actual method called is determined at runtime based on the object type, not the reference type.

Difference Between Compile-time and Run-time Polymorphism in Java

When discussing compile-time and run-time polymorphism, it's helpful to lay out their differences in a comparison table. This can clarify the distinct characteristics and use cases for each type.

Let's understand ​​Compile-time vs Run-time Polymorphism in Java in the comparison table 

When to Use Which Type of Polymorphism

Understanding when to use polymorphism in Java is key to writing clean, maintainable, and efficient code. Let’s look at two main types—compile time polymorphism and run time polymorphism—and when to choose each in real-world scenarios.

Compile Time Polymorphism (Method Overloading)

Use When: You need performance, predictability, or better readability in your code.

Compile time polymorphism occurs when multiple methods in the same class share the same name but differ in parameters (method overloading). It’s resolved by the compiler, making it faster and more predictable.

Ideal for:

• Utility/helper classes (e.g., math, formatting)
• Input validation
• Logging with varying details

Example:

public class Formatter {
    public String format(String text) {
        return text.trim();
    }

    public String format(String text, int width) {
        return String.format("%-" + width + "s", text);
    }
}

In this example, the right method is chosen during compile time, making the logic clear and optimized.

Choose compile time polymorphism when:

• You don’t need dynamic behavior.
• Code readability and performance matter more than flexibility.
• You want to handle different input variations cleanly.

Run Time Polymorphism (Method Overriding)

Use When: You need flexibility, extensibility, or interface-driven design.

Run time polymorphism happens when a subclass overrides a method from a superclass or interface. It’s resolved during execution, allowing different behaviors for different object types—even if referenced as a common type.

Ideal for:

• GUI event handling
• Extending API behavior
• Strategy pattern implementations

Example:

interface Notification {
    void send(String message);
}

class EmailNotification implements Notification {
    public void send(String message) {
        System.out.println("Email: " + message);
    }
}

class SMSNotification implements Notification {
    public void send(String message) {
        System.out.println("SMS: " + message);
    }
}

// At runtime Notification notifier = getNotifierBasedOnUserPreference();
notifier.send("Hello!");

Here, getNotifierBasedOnUserPreference() could return different implementations. The method send() is decided at run time, offering flexibility.

Choose run time polymorphism when:

• Your code must work with interfaces or abstract classes.
• You need different behaviors depending on the object type at runtime.
• You're building extensible, scalable systems.

Frequently Asked Questions

Can we override static methods?

No, static methods cannot be overridden. They are bound to the class, not to the instance of the class.

Is operator overloading supported in Java?

Java does not support operator overloading, except for the string concatenation operator (+), which is overloaded by the Java compiler.

How does run-time polymorphism benefit code reusability?

Run-time polymorphism allows for defining a common interface for different implementations, enabling the same code to work with objects of different classes, thus enhancing reusability.

Conclusion

Polymorphism is like a superpower in coding that lets us use the same piece of code in different ways. With compile-time polymorphism, we decide beforehand how we're going to use this superpower, making our code run fast because everything is set in stone from the start. But with run-time polymorphism, we get to make those decisions while the code is running, giving us the flexibility to adapt on the fly. This makes our code smart enough to handle different situations without needing a bunch of extra instructions. So, whether you're just starting out in coding or you're working on a big project, understanding how to use both types of polymorphism will help you write better, more efficient code that can do more with less.