Overloading and Overriding

OVERRIDING – Overriding a method means that its entire functionality is being replaced. Overriding is something done in a child class to a method defined in a parent class. To override a method a new method is defined in the child class with exactly the same signature as the one in the parent class. This has the effect of shadowing the method in the parent class and the functionality is no longer directly accessible.

Java provides an example of overriding in the case of the equals method that every class inherits from the granddady parent Object. The inherited version of equals simply compares where in memory the instance of the class references. This is often not what is wanted, particularly in the case of a String. For a string you would generally want to do a character by character comparison to see if the two strings are the same. To allow for this the version of equals that comes with String is an overriden version that performs this character by character comparison. when you extend a class and write a method in the derived class which is exactly similar to the one present in the base class, it is termed as overriding.

Example:

public class BaseClass{

public void methodToOverride()

{

//Some code here

}

}

public class DerivedClass extends BaseClass{

public void methodToOverride()

{

//Some new code here

}

}

As you can see, in the class DerivedClass, we have overridden the method present in the BaseClass with a completely new piece of code in the DerivedClass.

What that effectively means is that if you create an object of DerivedClass and call the methodToOverride() method, the code in the derivedClass will be executed. If you hadn’t overridden the method in the DerivedClass then the method in the BaseClass would have been called.

OVERLOADING -  Overloading of methods is a compiler trick to allow you to use the same name to perform different actions depending on parameters. when you have more than one method with the same name but different arguments, the methods are said to be overloaded.

Example:

public class OverLoadingExample{

public void add(int i, int j)

{

int k = i + j;

}

public void add(String s, String t)

{

int k = Integer.parseInt(s) + Integer.parseInt(t);

}

}

As you can see in the example above, we have the same method add() taking two parameters but with different data types. Due to overloading we can now call the add method by either passing it a String or int .