Java - Overriding
Categories: Java 8(JDK1.8)
The benefit of overriding is: ability to define a behavior that's specific to the subclass type, which means a subclass can implement a parent class method based on its requirement.
In object-oriented terms, overriding means to override the functionality of an existing method.
Example
Let us look at an example.
class Animal {
public void move() {
System.out.println("Animals can move");
}
}
class Dog extends Animal {
public void move() {
System.out.println("Dogs can walk and run");
}
}
public class TestDog {
public static void main(String args[]) {
Animal a = new Animal(); // Animal reference and object
Animal b = new Dog(); // Animal reference but Dog object
a.move(); // runs the method in Animal class
b.move(); // runs the method in Dog class
}
}
This will produce the following result −
Output
Animals can move
Dogs can walk and run
In the above example, you can see that even though b is a type of Animal it runs the move method in the Dog class. The reason for this is: In compile time, the check is made on the reference type. However, in the runtime, JVM figures out the object type and would run the method that belongs to that particular object.
Therefore, in the above example, the program will compile properly since Animal class has the method move. Then, at the runtime, it runs the method specific for that object.
Rules for Method Overriding
1. The argument list should be exactly the same as that of the overridden method.
2. The return type should be the same or a subtype of the return type declared in the original overridden method in the superclass.
3. 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.
4. Instance methods can be overridden only if they are inherited by the subclass.
5. A method declared final cannot be overridden.
6. A method declared static cannot be overridden but can be re-declared.
7. If a method cannot be inherited, then it cannot be overridden.