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Overriding in Java

Java Tutorials

When a method in a sub class has the same name and type signature as a method in its super class, then the method in the subclass is said to override the method in the super class.
When an overridden method is called from within a sub class, it will always refer to the version of that method defined by the sub class.
Similar to virtual functions in c++

Rules for method overriding:

  • 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 super class.

  • The access level cannot be more restrictive than the overridden method's access level. For example: if the super class method is declared public then the overridding method in the sub class cannot be either private or public. However the access level can be less restrictive than the overridden method's access level.

  • 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 overridden 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.

Example

class base
{
int a;
             
        void same()
        {
        a=10;
        System.out.println("Base class");
        System.out.println("Value of b is "+a);
        }

}

class drive extends base
{
int b;

     void same()
     {
     super.a=10;
     b=20;

     System.out.println("\ndrive class");
     System.out.println("Value of a is "+super.a);
     System.out.println("Value of b is "+b);
     }

}

class drive1 extends drive
{
int c;

     void same()
     {
     super.a=10;
     super.b=20;
     c=30;

     System.out.println("\nDrive one class");
     System.out.println("Value of a is "+super.a);
     System.out.println("Value of b is "+super.b);
     System.out.println("Value of c is "+c);
     }

}

class herit6
{
public static void main(String args[])
{
base ob1=new base();
ob1.same();

drive ob2=new drive();
ob2.same();

drive1 ob3=new drive1();
ob3.same();

}
}

Output

Java Tutorials