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29 : Function Overriding--Java Programming in Urdu

 Function Overriding / Method Overriding in Java
If subclass (child class) has the same method as declared in the parent class, it is known as method overriding in java. In other words, If subclass provides the specific implementation of the method that has been provided by one of its parent class, it is known as method overriding.

Rules for Java Method Overriding

  • method must have same name as in the parent class
  • method must have same parameter as in the parent class
  • must be IS-A relationship (inheritance).
  • The argument list should be exactly the same as that of the overridden method.
  • The return type should be the same or a subtype of the return type declared in the original overridden method in the superclass.
  • The access level cannot be more restrictive than the overridden method's access level. For example: If the superclass method is declared public then the overridding method in the sub class cannot be either private or protected.
  • Instance methods can be overridden only if they are inherited by the subclass.
  • A method declared final cannot be overridden.
  • A method declared static cannot be overridden but can be re-declared.
  • If a method cannot be inherited, then it cannot be overridden.
  • A subclass within the same package as the instance's superclass can override any superclass method that is not declared private or final.
  • A subclass in a different package can only override the non-final methods declared public or protected.
  • An overriding method can throw any uncheck exceptions, regardless of whether the overridden method throws exceptions or not. However, the overriding method should not throw checked exceptions that are new or broader than the ones declared by the overridden method. The overriding method can throw narrower or fewer exceptions than the overridden method.
  • Constructors cannot be overridden

Usage of Java Method Overriding

  • Method overriding is used to provide specific implementation of a method that is already provided by its super class.
  • Method overriding is used for run-time polymorphism

Example of  Overriding

class Bank{  
int getRateOfInterest(){return 0;}  
class SBI extends Bank{  
int getRateOfInterest(){return 8;}  
class ICICI extends Bank{  
int getRateOfInterest(){return 7;}  
class AXIS extends Bank{  
int getRateOfInterest(){return 9;}  
class Test2{  
public static void main(String args[]){  
SBI s=new SBI();  
ICICI i=new ICICI();  
AXIS a=new AXIS();  
System.out.println("SBI Rate of Interest: "+s.getRateOfInterest());  
System.out.println("ICICI Rate of Interest: "+i.getRateOfInterest());  
System.out.println("AXIS Rate of Interest: "+a.getRateOfInterest());