Inheritance

Multi-level Inheritance

Multi-level Inheritance is a process in which we have more than 2 classes.

A is base to B.

B is child to A.

B is base to C.

C is child to B.

Order of execution of classes:

1^st = A

2^nd = B

3^rd = C

Multiple Inheritance

Multiple Inheritance is a process in which we have multiple base classes and single child class. But in Java, we can’t do multiple inheritance using classes.

D extends A.

D extends B.

D extends C.

Interface

Interfaces are blocks in which we can declare methods but can’t provide the definition. All the methods declared in interface need to be defined always. We need to implement those methods in classes. By default, the methods in interfaces are public.

interface interface_name

{

            method declaration;

            method declaration;

:

}

Inheritance format:

class class_name implements interface_name

e.g. showing the importance of public access in interface:

Without using public (containing error):

Using public (no error):

Reason:

By default, the methods in interfaces are public while they are default in class. So, we need to specify the access specifier as public.

e.g. for Multiple inheritance:

Ques.

1.      Assume that a bank maintains 2 kinds of accounts for its customers. One is saving and the other is current account. The saving account provides compound interest and withdrawal facility but no checkbook facility. The current account provides checkbook facility but no interest. The current account holder should also maintain a min. balance and if the balance falls below the level, service charges are imposed.

2.      Create a class “Account” that stores - customer name, account no., and type of account. From this, derive the classes “current” and “saving” account to make them more specific to their requirements. Include the necessary methods to achieve the following task:

1.      Accept deposit from customer and update the balance.

2.      Display the balance.

3.      Compute and deposit interest.

4.      Permit withdrawal and update the balance.

5.      Check the min. balance, impose penalty if necessary and update the balance.

Do not use any constructor. Use methods to initialize the class members.

Abstract Classes

Abstract class is a class in which we have at least one abstract method. Abstract class always behaves as a base class.

Format:

abstract class class_name

{

}