Sadegh Aliakbary Sharif University of Technology Fall 2010

Agenda Packages Inheritance Fall 2010Sharif University of Technology2

Package A package contains a group of classes Organized together under a single namespace Packages organize classes belonging to the same category or providing similar functionality A package provides a unique namespace for the types it contains Classes in one package has the same folder Packages may contain other packages Hierarchy of packages Fall 2010Sharif University of Technology3

Some famous java packages java.util java.lang java.io Fall 2010Sharif University of Technology4

Java Packages import keyword Class Qualified Name = package-name + class-name For example java.lang.String java.lang.Math double sqrt = Math.sqrt(123); java.util.Scanner java.awt.Event org.w3c.dom.events.Event Fall 2010Sharif University of Technology5

Using packages Fall 2010Sharif University of Technology6

java.lang java.lang is implicitly imported Fall 2010Sharif University of Technology7

Package Access Remember public and private access specifiers The default access has no keyword It is commonly referred to as package access and sometimes friendly Other classes in the current package have access to that member To classes outside of this package, the member appears to be private. Fall 2010Sharif University of Technology8

Write a packaged java project Lets write … Fall 2010Sharif University of Technology9

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UML Class Diagram Fall 2010Sharif University of Technology13

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UML Class Diagram Fall 2010Sharif University of Technology17

Inheritance Java offers inheritance As any object oriented programming language Code reuse extends keyword is-a relationship Fall 2010Sharif University of Technology18

Faculty & Staff Attributes of staff is inherited to Faculty Fall 2010Sharif University of Technology19

Shapes Example Shape is an abstract class The definition of some methods should be changed in sub-classes getArea() getPerimeter() Fall 2010Sharif University of Technology20

Terminology Class Rectangle is inherited from class Shape Rectangle is a subclass of Shape Rectangle is a child of Shape Rectangle is a derived class of Shape Shape is the super-class of Rectangle Shape is the parent of Rectangle Shape is the base-class of Rectangle Rectangle is-a Shape Fall 2010Sharif University of Technology21

Inheritance in java Every class is inherited from class Object Primitive-types are not objects Object class has some operations equals() toString() … Every class adds some operations And changes some operations toString() Fall 2010Sharif University of Technology22

Quiz! Fall 2010Sharif University of Technology23

Quiz Draw a UML class diagram for these Classes Person (name, phoneNumber) Student (average, entranceYear) MS Student (thesis title) Instructor (offeredCourses) Fall 2010Sharif University of Technology24

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