1 Class 1 Lecture Topic Concepts, Definitions and Examples

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Class 1Lecture Topic

Concepts, Definitions and Examples

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Introduction to Java

• Object-oriented programming• Representation of reality• Everything is an object and every

object is a member of a class.• What are the objects in this picture?• What class does each object belong

to?• is-a relationship because you can say

My dog Toby is a dog.

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Instantiation

• An object is an instantiation of a class or a tangible example of a class.

• This object car is an example of the class car.

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What are these is-a relationships?

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Usefulness of Classes

• Reusable• Objects inherit attributes and methods from

classes

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Sample Program Design

• When you were planning your spring schedule, what things did automatically know about a course?

• What is it that all course have in common?

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Course Attributes

• Understand what a course entails from previous knowledge, these are the attributes.– attributes – these are your class variables

• a name, a number, etc.

• What things won’t you know? These are unique to the course?

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Classes also have Methods associated with them.

• methods – actions• get, set, doSomething

• You must set the date and time for a course.– setDate()– setTime()– getDate– getTime().

• What you called functions in C are called methods in Java.

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Two Parts to Object Oriented Programming

1. Create a class from which objects will be instantiated.

2. Write other classes to use the objects.

• a class client.• CourseApplication is the client class of

course.

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Creating a Class

• Assign a name to the class.• Determine attributes and methods that are

part of class.• For a class called Course, an instance

variable (attribute) might be: – courseNumber

• Two methods might be to set the course number and get the course number.

Course

courseNo:Integer

setCourseNo(Integer) : voidgetCourseNo(): Integer

Instance Variable

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First Step: Create a class header public class CourseApplicationAW

• An optional access modifier (public/abstract/final)

• The keyword class• Legal identifier that you choose.• After the above line is the opening {• Closing } goes after all Instance

Variables and Methods.

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A Java class Courseclass Course {

private int courseNo;

public void setCourseNo(int cNo){ courseNo = cNo;}

public int getCourseNo(){ return courseNo;}

}

Instance Variable

Methods

Course

courseNo:Integer

setCourseNo(Integer) : voidgetCourseNo(): Integer

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Using Classes

• Declaring a class does not create actual object

• Class is an abstract description• You might define an integer as

int someValue;

• Define an object of Course asCourse someCourse;

Notify the compiler that an integer someValue exists and reserve computer memory

When declaring someCourse not setting aside memory yet!

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Creating Objects

• Allocating memory:– someCourse = new Course();

• Or you could do in one step:Course someCourse = new Course();

– The keyword new indicates that someCourse is allocated memory.

– Course() is the method that constructs the Course object.

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Writing first program

• Need two classes• First is called the driver class,

– you will always have this class in your programs, – it will contain the main– Always call this class

SomethingApplicationYourInitials, replace Something with term relevant to program, CourseApplicationAW

• Second class will be Course

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The class CourseApplicationAW-First Attempt

public class CourseApplicationAW {

public static void main(String args[]){ Course someCourse = new Course();}

}•Allocates memory for someCourse, but no action takes place yet.

•CourseApplicationAW is the client class of course – (Has-A)

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The class Courseclass Course { private int courseNo;

public void setCourseNo(int cNo){courseNo = cNo;}

public boolean isFourThousandLevel(){if ((courseNo >=4000)&&(courseNo<5000))return true;else return false;}

}

The client class does not call these methods yet. Next Slide!

Course

courseNo:Integer

setCourseNo(Integer) : voidisFourThousandLevel(): Boolean

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New class CourseApplicationAW – uses methods of Course

public class CourseApplicationAW {public static void main(String args[]){Course someCourse = new Course();someCourse.setCourseNo(4567);System.out.println(someCourse.isFourThousandLevel());

}}

dot operatorCourseApplicationAW

main(String) : void

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Public and not Public

• All our classes are placed in same file.• Only one public class allowed• Other classes are private (not accessible

from outside this program).• Many other ways to approach this…

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Improving the class Course

• What attributes can you add to the class Course?

• What methods can you add?

Course

courseNo:Integer

setCourseNo(Integer) : voidisFourThousandLevel(): Boolean

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Moving On - Using Forte

1. Pictorially2. Demonstrate Forte3. You try it…

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Starting• Select/Open Forte for Java CE• (slow)• check the version number for Java

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Forte for Java

helpful hints window – close if appears

tabs – select Editing tab

indicates if a program is running

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New ProjectSelect Project/New Project

Create New Project Window, name project – YourInitialsFirstProjselect OK

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Choose New

If see above window – select Yes

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Full Screen Image – working in window that says: Mount Directory

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Mount Directory

• This is your working directory • your files are saved here• MUST be a directory• Best to be a directory on floppy• No directory on floppy, can make one at

this stage.

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Mount Directory

make directory – if needed

File Name refers to directory NOT a file.

Mount – mounts workingdirectory

Created New Folder (you can name it), click on New Folder ONCE,Select Mount.New Folder appears as FileName.

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Explorer Window

Shows mounted directory, you canmount any number of directories thisway.

This Tab shows the project youcreated, any files you create go intoproject.

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Java File

• all java program files end in .java• done automatically• compiled files are .class• Need to create an empty java file.

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Creating Program File• highlight (left click on

mounted directory)• right click to bring up

menu• select

new,classes,empty

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Selecting Name – Must be IDENTICAL to public class

VERY IMPORTANT – MUST MATCH CASE – Programming Convention – all Class Names – Capitalize each word

Type NameSelect Finish

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Respond yes

This places the file within the project you created.If select Project tab will see:

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File Created and Ready to Code

Your code goes here

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Right Click in Source Editor will bring up menu to Save, Compile,

Execute, etc.

Reformat code – indentscode for you – nice!

Save Often – only lets you saveif you’ve made a change to code

Compile – checks forcompilation error

Execute – runsprogram

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Type Code Here

Save, Compile, Execute…

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System.out.println – prints outputto this window (usually at bottom

of screen).

true is the boolean value of the response towhether the courseNo is >=4000 and less than 5000

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When You’re Finished

• Unmount file system• exit Forte

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Live Example

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Lab Work•Familiarization with Forte for Java•Writing first program•Improving program•Writing second program

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Next Week

• Email Survey• Discussion List Assignment• Quiz – see syllabus – (practice using Forte)• write some small programs using two

classes.• Try the example programs pointed to from

syllabus.