Overriding vs. Overloading in Java

overloading-vs-overriding

Overriding and Overloading are two very important concepts in Java. They are confusing for Java novice programmers. This post illustrates their differences by using two simple examples.

1. Definitions

Overloading occurs when two or more methods in one class have the same method name but different parameters.

Overriding means having two methods with the same method name and parameters (i.e., method signature). One of the methods is in the parent class and the other is in the child class. Overriding allows a child class to provide a specific implementation of a method that is already provided its parent class.

2. Overriding vs. Overloading

Here are some important facts about Overriding and Overloading:

1). The real object type in the run-time, not the reference variable's type, determines which overridden method is used at runtime. In contrast, reference type determines which overloaded method will be used at compile time.
2). Polymorphism applies to overriding, not to overloading.
3). Overriding is a run-time concept while overloading is a compile-time concept.

3. An Example of Overriding

Here is an example of overriding. After reading the code, guess the output.

class Dog{
    public void bark(){
        System.out.println("woof ");
    }
}
class Hound extends Dog{
    public void sniff(){
        System.out.println("sniff ");
    }
 
    public void bark(){
        System.out.println("bowl");
    }
}
 
public class OverridingTest{
    public static void main(String [] args){
        Dog dog = new Hound();
        dog.bark();
    }
}

Output:

bowl

In the example above, the dog variable is declared to be a Dog. During compile time, the compiler checks if the Dog class has the bark() method. As long as the Dog class has the bark() method, the code compilers. At run-time, a Hound is created and assigned to dog. The JVM knows that dog is referring to the object of Hound, so it calls the bark() method of Hound. This is called Dynamic Polymorphism.

4. An Example of Overloading

class Dog{
    public void bark(){
        System.out.println("woof ");
    }
 
    //overloading method
    public void bark(int num){
    	for(int i=0; i<num; i++)
    		System.out.println("woof ");
    }
}

In this overloading example, the two bark method can be invoked by using different parameters. Compiler know they are different because they have different method signature (method name and method parameter list).

References:
1) Defining Method. This tutorial is from Oracle, it explains the components of a method and which of them are used by compiler to differentiate methods.

Category >> Basics  
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  1. […] Overloading vs Overriding […]

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  4. Elvin Mirze on 2014-6-3

    Great!

  5. ling maaki on 2015-1-19
  6. Mark Loh on 2015-5-10

    method overloading is the process of defining more than one function in a class with the same name but different argument lists. at the line of function calling, the complier will invoke the correct one by using the type and member of the argument.

  7. SANAJIT GHOSH on 2015-8-4

    very nice picture to explain

  8. komal pandit on 2016-7-14
  9. Allen Scott on 2016-9-6
  10. ansaik on 2017-2-19

    very easy but one question.
    what is Polymorphism

  11. Prasad Biradar on 2017-3-20

    single action can be performed by many ways….
    2 types
    1.compile time-overloding
    2 run time-over riding

  12. Prince Dudley on 2017-5-23

    This is a very nice article that demonstrates the difference.

  13. JAC_JustAnotherCoder on 2017-5-28

    thanks 🙂

  14. Happy Programmer on 2017-10-17

    Thank you very much for this, I now know more about programming. Keep it up!

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