Object oriented experiment 1

Object oriented experiment
2

Objective:



Package



Reference data type



Variable scope



Overloading





Java Packages



State: property, or attribute



Behavior: function/action, or method




Java hierarchically organizes classes into packages*

o

java.lang

o

java.text

o

ja
va.util

o

…




Classes need to be referred using its complete name (package + class
name): for example, java.util.Calendar

o

Packages can be “imported” to avoid writing package names every
time you use a class (except java.lang)


import java.util.*;





Using Pack
age



Organizing your classes into packages

o

A class can only be in one package

o

No duplicate class definition in the same package

o

Put the package statement at the beginning

o

Packages correspond to directories in local file system




Examples:

package cis3270;

p
ackage cis3270.assignment;

package cis3270.lecture.web;





Default Package



A class without any package defined is in a “default package”



The default package is NOT the root package!

o

Classes in the default package cannot be referenced outside the
default pac
kage




Reference Data Type



Reference data type stores memory address (reference) as its value




Objects are reference data type





Object Assignment



Objects are assigned by reference





Variable Scope



Member variable

o

Something like a global variable within t
he class



Local variable

o

Method parameter

o

Method level variable

o

Block level variable



A variable is effective at its declaration level and all sub
-
levels






Method Overloading



Multiple methods share the same method name, but each
of them is with a
different parameter set (different method signature)

o

Examples:

int
method
()

int
method
(int a)

String
method
(int a, String b)

void
method
(int a, int b)

void
method
(String a, int b)


Or:

System.out.print(…)





Constructor Overloading



Like me
thods, constructors can be overloaded



This offers greater flexibility and convenience of creating objects


Summary



Object orientation is more of a way of thinking/modeling, rather than just a
programming method



Organize your classes effectively using packa
ges



Design overloaded methods and constructors effectively



Tools :

NetBeans or JCreator
or JDK


Experiment

1
-

Open NetBeans tool

2
-

File


New


select "Java Classes" as shown in the figure
:




3
-

Then press "Next", then "
Complex
" in the class name as shown in t
he figure:




4
-

Then press "Finished", then the following code will appears


public class
Complex

{




public
Complex
() {


}

}


5
-

Then complete the code to be like the following:


public class Complex {




private float re;




private fl
oat im;




private static int instNo=0;




/** Creates a new instance of Complex */


public Complex() {


this(0,0);


}




public Complex(float r, float i) {


re= r;


im=i;


instNo++;


}




public

Complex(Complex c) {


this(c.re,c.im);




}


public float getReal() {


return re;


}




public float getImaginary() {


return im;


}




public void setReal(float r) {


re=r;


}




publi
c void setImaginary(float i) {


im=i;


}




public Complex add(Complex c) {


re += c.re;


im +=c.im;




return this;


}




public Complex sub(Complex c) {


re
-
= c.re;


im
-
=c.im;




return this;


}




public static int getNoInstance() {


return instNo;


}




public String toString() {


return "Real =" + re + " Imaginary=" + im;


}




public static Complex add(Complex c1, Complex c2)
{


Complex c3 = new Complex(c1.re+c2.re ,c1.im+ c2.im);


return c3;


}




public static Complex sub(Complex c1, Complex c2) {


Complex c3 = new Complex(c1.re
-

c2.re ,c1.im
-

c2.im);


return c3;


}




public st
atic void main(String srg[]){


Complex c1 = new Complex(1,2);


Complex c2 = new Complex();


Complex c3 = new Complex(c1);


Complex c4 = new Complex(3,4);


System.out.println(c1);


System.out.println(c2);


Sy
stem.out.println(c3);


System.out.println(c4);


c2.add(c1);


Complex c5 = c1;


c1.sub(c4);


System.out.println(c3);


System.out.println(c5);




Complex c6 = Complex.add(c3,c4);


System.out.prin
tln(c6);




System.out.println("No of Obkect Created = " +
Complex.getNoInstance());








}

}

6
-

Press "F6" or open menu Build


Execute

7
-

W
rite down the result :

1

2

3

4

5

6

7

8