Distinguishing Dynamic and Static Polymorphism in Java

Understanding the difference between dynamic and static polymorphism is crucial in object-oriented programming with Java. This article will provide a simplified explanation and example to elucidate this concept.

Dynamic vs. Static Polymorphism

Polymorphism allows a single method name to have multiple implementations depending on the object type calling it. There are two primary types of polymorphism:

• Dynamic Polymorphism (Runtime Binding): Method calls are resolved at runtime based on the actual object's class. It occurs with method overriding in subclasses and is also known as late binding.
• Static Polymorphism (Compile-Time Binding): Method calls are resolved at compile-time based on the declared type of the reference variable. It occurs with method overloading in the same class and is also known as early binding.

Method Overloading

Method overloading is a form of static polymorphism where multiple methods with the same name exist in the same class but differ in their parameters. When calling an overloaded method, Java determines the appropriate method to invoke based on the number and types of arguments passed in.

Code Example (Method Overloading):

class Calculation {
  void sum(int a, int b) { System.out.println(a   b); }
  void sum(int a, int b, int c) { System.out.println(a   b   c); }

  public static void main(String[] args) {
    Calculation obj = new Calculation();
    obj.sum(10, 10, 10); // Output: 30
    obj.sum(20, 20); // Output: 40
  }
}

Method Overriding

Method overriding is a form of dynamic polymorphism where methods with the same name and signature are declared in different classes but share a common parent class. When calling an overridden method, Java determines the method to invoke based on the object's actual class at runtime.

Code Example (Method Overriding):

class Animal {
  public void move() {
    System.out.println("Animals can move");
  }
}

class Dog extends Animal {

  public void move() {
    System.out.println("Dogs can walk and run");
  }
}

public class TestDog {

  public static void main(String[] args) {
    Animal a = new Animal(); // Animal reference and object
    Animal b = new Dog(); // Animal reference but Dog object

    a.move(); // Output: Animals can move

    b.move(); // Output: Dogs can walk and run
  }
}