Dynamic Method Dispatch in Java

Dynamic method dispatch is a mechanism by which a call to an overridden method is resolved at runtime rather than compile-time. This allows for a subclass to have a different implementation of a method that is inherited from a superclass.

In Java, dynamic method dispatch is achieved through the use of virtual method invocation. When an overridden method is called through a superclass reference, Java determines which version of the method to execute based on the type of the object being referred to at the time of the method call.

For example, consider the following code:

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

class Dog extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Woof!");
    }
}

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

In this code, Animal has a method called makeSound, and both Dog and Cat classes override this method to provide their own implementations. If we have a reference to an Animal type and call the makeSound method, the version of the method that is executed will be the one defined in the Animal class. However, if we have a reference to a Dog or Cat type and call the makeSound method, the version of the method that is executed will be the one defined in the Dog or Cat class, respectively.

Following is an example of how this works in practice:

Animal a = new Animal();
a.makeSound(); // prints "Some generic animal sound"

Animal d = new Dog();
d.makeSound(); // prints "Woof!"

Animal c = new Cat();
c.makeSound(); // prints "Meow!"

In the first line of this example, we create a new Animal object and assign it to a reference of type Animal. When we call the makeSound method on this object, the version of the method defined in the Animal class is executed.

In the second and third lines, we create a Dog object and a Cat object, respectively, and assign them to references of type Animal. Even though the objects being referred to are of type Dog and Cat, respectively, the reference variables are of type Animal, so when we call the makeSound method on these references, the version of the method defined in the Animal class is called.

Dynamic method dispatch is an important feature of object-oriented programming languages because it allows for polymorphism, or the ability of different objects to respond differently to the same method call. This can greatly simplify code by allowing a single method call to handle a variety of different cases, rather than having to write separate method calls for each case.