Java – Static Vs. Dynamic Binding in Java

dynamic-bindingjavastatic-binding

I'm currently doing an assignment for one of my classes, and in it, I have to give examples, using Java syntax, of static and dynamic binding.

I understand the basic concept, that static binding happens at compile time and dynamic binding happens at runtime, but I can't figure out how they actually work specifically.

I found an example of static binding online that gives this example:

public static void callEat(Animal animal) {
    System.out.println("Animal is eating");
}

public static void callEat(Dog dog) {
    System.out.println("Dog is eating");
}

public static void main(String args[])
{
    Animal a = new Dog();
    callEat(a);
}

And that this would print "animal is eating" because the call to callEat uses static binding, but I'm unsure as to why this is considered static binding.

So far none of the sources I've seen have managed to explain this in a way that I can follow.

Best Answer

From Javarevisited blog post:

Here are a few important differences between static and dynamic binding:

  1. Static binding in Java occurs during compile time while dynamic binding occurs during runtime.
  2. private, final and static methods and variables use static binding and are bonded by compiler while virtual methods are bonded during runtime based upon runtime object.
  3. Static binding uses Type (class in Java) information for binding while dynamic binding uses object to resolve binding.
  4. Overloaded methods are bonded using static binding while overridden methods are bonded using dynamic binding at runtime.

Here is an example which will help you to understand both static and dynamic binding in Java.

Static Binding Example in Java

public class StaticBindingTest {  
    public static void main(String args[]) {
        Collection c = new HashSet();
        StaticBindingTest et = new StaticBindingTest();
        et.sort(c);
    }
    //overloaded method takes Collection argument
    public Collection sort(Collection c) {
        System.out.println("Inside Collection sort method");
        return c;
    }
    //another overloaded method which takes HashSet argument which is sub class
    public Collection sort(HashSet hs) {
        System.out.println("Inside HashSet sort method");
        return hs;
    }
}

Output: Inside Collection sort method

Example of Dynamic Binding in Java 

public class DynamicBindingTest {   
    public static void main(String args[]) {
        Vehicle vehicle = new Car(); //here Type is vehicle but object will be Car
        vehicle.start(); //Car's start called because start() is overridden method
    }
}

class Vehicle {
    public void start() {
        System.out.println("Inside start method of Vehicle");
    }
}

class Car extends Vehicle {
    @Override
    public void start() {
        System.out.println("Inside start method of Car");
    }
}

Output: Inside start method of Car

Related Topic