Difference Between Compile-Time and Runtime Polymorphism in Java

Polymorphism is a fundamental concept in Object-Oriented Programming (OOP). The term polymorphism refers to the existence of many forms. The capability enhances code flexibility, modularity, and maintainability.

There are the following two types of polymorphism in Java

• Compile-Time Polymorphism (Static Polymorphism)
• Runtime Polymorphism (Dynamic Polymorphism)

Compile-Time Polymorphism (Static Binding)

Compile-time polymorphism occurs when a method to be executed is selected during the compilation process. It is also known as static binding or early binding. It is usually accomplished through method overloading, i.e., having several methods with the same name but different parameter lists within the same class.

Upon compiling the code, the Java compiler examines the method call and adjusts it accordingly, depending on the number of parameters and their types. Then, it binds the call with the applicable method.

To read more Compile Time Polymorphism in Java

Output:

 8 5.6 6 

Here, the add() method is overloaded with different parameter signatures. The compiler binds the method call to the appropriate method at compile time based on the argument types.

Advantages of Compile-Time Polymorphism

• Improves code readability through method reuse.
• Faster execution due to early binding.
• Easier to test and understand since the behaviour is fixed.

Runtime Polymorphism (Dynamic Binding)

Runtime polymorphism occurs when a method call is resolved at runtime, rather than during compilation. It is also known as dynamic binding or late binding, or dynamic method dispatch. It is usually achieved by method overriding, in which a subclass provides a specific implementation to a method that already exists within its superclass.

It is a polymorphism case if the superclass reference variable is used to reference an object of a subclass, and the method called depends on the actual type of the object rather than the type of the reference variable. This choice occurs during the program's execution, and therefore, it is called "runtime". Note that

• It works only with method overriding, not method overloading.
• The method must be non-static and non-private, because those do not participate in runtime polymorphism.

Output:

 Dog barks Cat meows 

In this case, even though the reference variable is of type Animal, the actual method that gets called depends on the object (Dog or Cat). The binding occurs at runtime, making this a dynamic method dispatch.

Advantages

• Enables dynamic behavior and code flexibility.
• Supports abstraction and design patterns, such as Strategy, State, and Factory.
• Allows code to be extended and maintained easily with minimal changes.

Differences Between Compile-Time and Runtime Polymorphism

Which one to use and when?

Use Compile-Time Polymorphism When,

1. We need multiple methods that perform similar operations but with different input types or counts.
2. We want faster performance since the method calls are resolved during compilation.
3. We do not need dynamic behavior based on the object type.

Use Runtime Polymorphism When,

1. We want to use abstraction or interfaces.
2. We want different implementations of the same method in different classes.
3. We want to write flexible and scalable code using inheritance and polymorphic behavior.

Why is polymorphism important in Java?

Polymorphism is critical in Java because it supports interface-based design and encourages loose coupling. It means your code interacts with interfaces or superclasses rather than concrete implementations, enabling:

• Easier maintenance and extension without modifying existing code.
• Cleaner implementation of design patterns like Strategy, Observer, and Command.
• Reduced duplication, as you can reuse general behavior and override specifics.

Java Compile-Time and Runtime Polymorphism MCQs

1. Which of the following is an example of compile-time polymorphism in Java?

1. Method Overriding
2. Method Overloading
3. Constructor Chaining
4. Using abstract classes

2. What decides the method to be executed in runtime polymorphism?

1. The method name only
2. The reference type
3. The object type
4. The return type

3. Which of the following statements is true about compile-time polymorphism?

1. It is achieved through the use of interfaces.
2. It requires inheritance.
3. It occurs through method overloading.
4. It is resolved at runtime.

4. What is the primary advantage of runtime polymorphism?

1. Improves performance
2. Allows operator overloading
3. Supports dynamic behavior and flexibility
4. Avoids the need for method overloading

5. Which of the following features is NOT associated with runtime polymorphism?

1. Method overriding
2. Dynamic binding
3. Use of inheritance
4. Compile-time method resolution