Modifying a super class method in the sub class is called method overriding. Using method overriding, we can change super class method according to the requirements of sub class.
What are the rules to be followed while overriding a method?
- Must have the same argument list.
- Must have the same return type, except that as of Java 5, the return type can be a subclass—this is known as a covariant return.
- Must not have a more restrictive access modifier.
- May have a less restrictive access modifier.
- Must not throw new or broader checked exceptions.
- May throw fewer or narrower checked exceptions, or any unchecked exception.
No, Static methods can not be overridden.
Explanation: Static method are not associated with any object.Even if we invoke any static method of the class on any object, at compile time, complier replaces the reference variable with the class name, therefore they can not be overridden.
What happens if we change the arguments of overriding method?
If we change the arguments of overriding method, then that method will be treated as overloaded not overridden.
Can we override protected method of super class as public method in the sub class?
Yes. We can change the visibility of overriding methods, but we can only increase it and can’t reduce it.
Can we change the return type of overriding method from Number type to Integer type?
Yes. The return type of the overriding method can be a sub-type of return type of super class(also knows as co-variance).
Can we override a super class method without throws clause as a method with throws clause in the sub class?
Yes, but only with unchecked type of exceptions.
Can we change an exception of a method with throws clause from NullPointerException to ArrayIndexOutOfBoundException while overriding it?
Yes. Overridden method may throw NullPointerException or it’s sub class exception or any unchecked type of exceptions.
What is the use of super keyword?
Using super keyword, we can refer super class version of overridden method in the sub class.
Can we override private methods?
No, we can not override private methods because private method is not visible in the sub class.
Can we remove throws clause of a method while overriding it?
Yes. You can remove throws clause of a method while overriding it.
What is method overloading?
When a class has more than one method with same name but different parameters, then we call those methods are overloaded. Overloaded methods will have same name but different number of arguments or different types of arguments.
What is method signature? What are the things it consist of?
Method signature is used by the compiler to differentiate the methods. Method signature consist of three things.
- Method name
- Number of arguments
- Types of arguments
Yes. Overloaded methods can be either static or non static.
Compiler uses method signature to check whether the method is overloaded or duplicated. Duplicate methods will have same method signatures i.e same name, same number of arguments and same types of arguments. Overloaded methods will also have same name but differ in number of arguments or else types of arguments.
Is it possible to have two methods in a class with same method signature but different return types?
No, compiler will give duplicate method error. Compiler checks only method signature for duplication not the return types. If two methods have same method signature, straight away it gives compile time error.
Can overloaded methods be synchronized?
Yes. Overloaded methods can be synchronized.
Yes, we can overload main() method. A class can have any number of main() methods but execution starts from public static void main(String args) only.
Can we declare overloaded methods as final?
Yes, we can declare overloaded methods as final.