Download class1-Lecture

Class 1
Lecture 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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Instance Variable
Course
Creating a Class
courseNo:Integer
setCourseNo(Integer) : void
getCourseNo(): Integer
• 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.
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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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Course
courseNo:Integer
A Java class Course
class Course
setCourseNo(Integer) : void
getCourseNo(): Integer
{
private int courseNo;
Instance
Variable
public void setCourseNo(int cNo)
{
courseNo = cNo;
}
public int getCourseNo()
{
return courseNo;
}
}
Methods
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Using Classes
• Declaring a class does not create actual
object
• Class is an abstract description
Notify the compiler
• You might define an integer as
that an integer
int someValue;
• Define an object of Course as
Course someCourse;
someValue exists and
reserve computer
memory
When declaring
someCourse not
setting aside memory
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yet!
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 CourseApplicationAWFirst 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 Course
class Course {
private int courseNo;
public void setCourseNo(int cNo)
{
courseNo = cNo;
}
}
The client class
does not call
these methods
yet. Next Slide!
public boolean isFourThousandLevel()
{
if ((courseNo >=4000)&&(courseNo<5000))
Course
return true;
courseNo:Integer
else return false;
setCourseNo(Integer) : void
isFourThousandLevel(): 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 operator
CourseApplicationAW
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) : void
isFourThousandLevel(): Boolean
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Moving On - Using Forte
1. Pictorially
2. Demonstrate Forte
3. 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
tabs –
select
Editing
tab
indicates
if a
program
is running
helpful
hints
window –
close if
appears
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New Project
Select Project/New Project
Create New Project Window, name project – YourInitialsFirstProj
select 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
Mount – mounts working
directory
File Name refers to directory NOT a file.
Created New Folder
(you can name it), click on
New Folder ONCE,
Select Mount.
New Folder appears as File
Name.
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Explorer Window
Shows mounted directory, you can
mount any number of directories this
way.
This Tab shows the project you
created, any files you create go into
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project.
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
Type Name
Select Finish
VERY IMPORTANT – MUST MATCH CASE –
Programming Convention – all Class Names – Capitalize each word
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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.
Compile –
checks for
compilation
error
Reformat code – indents
code for you – nice!
Save Often – only lets you save
if you’ve made a change to code
Execute – runs
program
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Type Code Here
Save, Compile, Execute…
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System.out.println – prints output
to this window (usually at bottom
of screen).
true is the boolean value of the response to
whether 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.
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