Java - Covariant Method Overriding with Examples

The covariant method overriding approach, implemented in Java 5, helps to remove the client-side typecasting by enabling you to return a subtype of the overridden method's actual return type.

Covariant Method overriding means that when overriding a method in the child class, the return type may vary. Before java 5 it was not allowed to override any function if the return type is changed in the child class. But now it is possible only return type is subtype class.

Overriding the Covariant approach provides a way for you to return the subtype of the overridden method's actual return class. It helps to eliminate the burden of typecasting from the programmer. This method is often used when an object is returned by the overriding method.

Let's have an example to understand it. The function clone() returns the object of the class Object. But since each class is the child of the object class, we will return the object of our own class. Suppose the overriding concept of the Covariant mechanism has not yet been implemented. Then we still need to cast the object. If the cast is not used then "Object cannot be converted to Student" error occurs.

Example 1:

Name : Kapil, RollNo: 1, Class Name : MCA
Name : Sachin, RollNo: 2, Class Name : MCA

In the above example when we are using the clone() method, it returns the object of Object class, and then we typecast it into Student class.

Student student2 = (Student) student1.clone();

Suppose we use the clone method in the program 10 times, so we need to type it each time. We should override the Covariant approach to solve these types of issues. We will return the object of the student class rather than the object class by using the concept of Covariant.

Let's see how we're going to use it.

Example 2:

Name : Kapil, RollNo: 1, Class Name : MCA
Name : Sachin, RollNo: 2, Class Name : MCA

We can see above, since we're returning a Student class object instead of an Object class, we don't need to type the object returned from the clone() method into Student.