Java- language Lecture 7

JAVA
FUNDAMENTALS
Eng : Hatem Abd El-Salam
Lecture 7

Agenda
 Wrapper classes
 Abstraction
 Interface
 Delection
© 2016 by Eng. Hatem Abd El-Salam

Wrapper classes

Wrapper classes (Cont.)

Abstraction
 Abstraction is a process of hiding the implementation details and showing only
functionality to the user.
 Another way, it shows only important things to the user and hides the internal
details .
for example: sending sms, you just type the text and send the message. You don't
know the internal processing about the message delivery.
 Abstraction lets you focus on what the object does instead of how it does it

Abstraction (Cont.)
Ways to achieve Abstraction
 There are two ways to achieve abstraction in java
1. Abstract class (0 to 100%)
2. Interface (100%)
Abstract class in Java
• A class that is declared as abstract is known as abstract class. It needs to be
extended and its method implemented. It cannot be instantiated.
• It can have abstract and non-abstract methods (method with body).

Abstraction (Cont.)
Abstract method
 A method that is declared as abstract and does not have implementation is known
as abstract method.

Abstraction (Cont.)
Rules
 If there is any abstract method in a class, that class must be abstract.
 If you are extending any abstract class that have abstract method, you must either
provide the implementation of the method or make this class abstract.

Interface
 An interface in java is a blueprint of a class. It has static constants and abstract
methods only.
 The interface in java is a mechanism to achieve fully abstraction. There can be only
abstract methods in the java interface not method body. It is used to achieve fully
abstraction and multiple inheritance in Java.
 Java Interface also represents IS-A relationship.
 It cannot be instantiated just like abstract class.

Interface (Cont.)
Why use Java interface ?
 There are mainly three reasons to use interface. They are given below.
1. It is used to achieve fully abstraction.
2. By interface, we can support the functionality of multiple inheritance.
3. It can be used to achieve loose coupling.

Interface (Cont.)
 The java compiler adds public and abstract keywords before the interface method
and public, static and final keywords before data members.

Interface (Cont.)
Understanding relationship between classes and interfaces

Interface (Cont.)

Interface (Cont.)
Multiple inheritance in Java by interface

Delegation
Q:What are delegates?
When an object receives a request, the object can either handle the request itself or
pass the request on to a second object to do the work. If the object decides to pass
the request on, you say that the object has forwarded responsibility(delegate) for
handling the request to the second object.
Simple examples

Complex examples

Name : Eng. Hatem Abd El-Salam
Email : Hatemabdelsalam@Hotmail.com
LinkedIn : linkedin.com/in/hatemabdelsalam
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Java- language Lecture 7

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