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OBJECT ORIENTED PROGRAMMING:
FROM C++ TO JAVA AND C++ .NET
The programming environment for this session:
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Java Compiler/IDE: JGRASP
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Project: Just Java Old Plain Code
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Project Settings: None, all default settings
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OS: Win Xp Pro SP2 + updates + patches…, 2GB RAM, Intel Core 2 Duo…
Answer: This is just a working java program skeleton of class definition and object instantiation. |
// this is a Java package where all the related classes (built-in)
// reside. For every class, there are many methods that we can invoke.
// In this case we are going to use the Scanner class
import java.util.Scanner;
//---------------------------------------------------------
// class Secret, nothing is secret here...
//---------------------------------------------------------
public class Secret
{
// data declarations, variables with their own data types
// initialized with values that will be used as default constructor's
// values if there is no one to be found...initialized values
// shown are defaults
String name = "";
int age = 0, weight = 0;
double height = 0.0;
// constructor that will overwrite the default one...
// the name is same as the class without any return type
public Secret(String coname, int coage, int coweight, double coheight)
{
// using a pre-defined class, instantiating a new Scanner object
Scanner readdata = new Scanner(System.in);
// invoking the print() method of System.out object
System.out.print("Enter your name: ");
// invoking the nextLine() method of Scanner class (System.in object)
coname = readdata.nextLine();
setName(coname);
System.out.print("Enter your age: ");
coage = readdata.nextInt();
setAge(coage);
System.out.print("Enter your weight: ");
coweight = readdata.nextInt();
setWeight(coweight);
System.out.print("Enter your height: ");
coheight = readdata.nextDouble();
setHeight(coheight);
print();
}
//---------------------------------------------------------
// The following methods will be used when the instantiated
// object call them from the main().....
// in this program, however call from main() may be overwritten
// by the constructors....
//---------------------------------------------------------
// setName method() - set name to a new value
public void setName(String yourname)
{
name = yourname;
}
// setAge method() - set the age to a new value
public void setAge(int yourage)
{
age = yourage;
}
// setWeight method() - set the weight to a new value
public void setWeight(int yourweight)
{
weight = yourweight;
}
// setHeight method() - set the height to a new value
public void setHeight(double yourheight)
{
height = yourheight;
}
// getName method() - return the name
public String getName()
{
return name;
}
// getAge method() - return the age
public int getAge()
{
return age;
}
// getWeight method() - return the weight
public int getWeight()
{
return weight;
}
// getHeight method() - return the height
public double getHeight()
{
return height;
}
// print method() - output all data to standard output
public void print()
{
System.out.println();
System.out.println("Your name is: " + getName() + ".");
System.out.println("Your age is: " + getAge() + " years old.");
System.out.println("Your weight is: " + getWeight() + " kgs.");
System.out.println("Your height is: " + getHeight() + " cms.");
}
// main() method - the start of this program execution point
public static void main(String[] args)
{
// instantiate an object of type Secret class
// giving some dummy values that will be overwritten by
// the 'Constructor with parameters'.
// this instantiation will invoke Constructor with parameters
Secret mysecret = new Secret("Nazri",30,56,165);
// other codes.....
}
}
A Sample output:
Enter your name: Ahmad Nazri bin Zainol
Enter your age: 48
Enter your weight: 53
Enter your height: 165
Your name is: Ahmad Nazri bin Zainol.
Your age is: 48 years old.
Your weight is: 53 kgs.
Your height is: 165.0 cms.
Enter your name: Meg Ryan Jr.
Enter your age: 40
Enter your weight: 50
Enter your height: 170
Your name is: Meg Ryan Jr..
Your age is: 40 years old.
Your weight is: 50 kgs.
Your height is: 170.0 cms.
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Implement a class Rectangle that has methods getArea(), getPerimeter() and getDiagonal(). In the constructor, supply the length and width of the rectangle. Write a program that asks the user for the length and width of a rectangle. Then creates an object of Rectangle and prints its area, perimeter and diagonal length. (Use the Pythagorean formula to calculate length of the diagonal)
Answer: Another user defined class and object with 3 methods that do their own specific tasks.
import java.util.Scanner;
import java.text.DecimalFormat;
//---------------------------------------------------------
// class Rectangle: Area, Perimeter and Diagonal
//---------------------------------------------------------
// For rectangles with the sides a, b, is:
// area = a * b
// perimeter = 2*(a + b)
// diagonal = root of ((a*a)+(b*b))
public class Rectangle
{
// member variables, used as default constructor values
// if constructor not provided...
double height = 0.0 ;
double width = 0.0;
// constructor
Rectangle(double h, double w)
{
height = h;
width = w;
}
// get the rectangle perimeter
public double getPerimeter(double h, double w)
{
return 2*(h+w);
}
// get the rectangle area
public double getArea(double h, double w)
{
return (h*w);
}
// get the rectangle diagonal
public double getDiagonal(double h, double w)
{
return Math.sqrt(((h*h)+(w*w)));
}
// main() method - the start of this program execution point
public static void main(String[] args)
{
double recheight = 0.0, recwidth = 0.0;
// instantiate a standard input object
Scanner readuserinput = new Scanner(System.in);
// prompt user for rectangle's height and width
System.out.print("Enter rectangle height and width (e.g: 10 10): ");
// read and store rectangle's height and width
recheight = readuserinput.nextDouble();
recwidth = readuserinput.nextDouble();
// instantiate and initialize the myrectangle object
// of type rectangle class
Rectangle myrectangle = new Rectangle(recheight, recwidth);
// do some formatting for the double
DecimalFormat fmt = new DecimalFormat("0.##");
// print rectangle's area, perimeter and diagonal to standard output
System.out.println("The rectangle area is: " + fmt.format(myrectangle.getArea(recheight,recwidth)));
System.out.println("The rectangle perimeter is: " + fmt.format(myrectangle.getPerimeter(recheight,recwidth)));
System.out.println("The rectangle diagonal is: " + fmt.format(myrectangle.getDiagonal(recheight,recwidth)));
}
}
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Define a class named MyDay that implements the day of the week in a program. The class MyDay should store the day, such as Sun for Sunday. The program should be able to perform the following operations on an object of the type MyDay:
Set the day.
Print the day.
Return the day.
Return the next day.
Return the previous day.
The class should also have the appropriate constructor. Write a program to test all the operations for class MyDay as described in a. to e. above.
Answer: Day class and object manipulation.
import java.util.*;
//------------------------------------------------------------------
// MyDay class. Playing with day of week...
//------------------------------------------------------------------
public class MyDay
{
// instantiate standard input object
static Scanner readinput = new Scanner(System.in);
// member variable, private by default
String day;
// constructor with "Sunday" value
public MyDay(String day)
{
day = "Sunday";
}
// set the day
public void setDay(String theDay)
{
day = theDay;
}
// print or return the day
public String getDay()
{
return day;
}
// print the day, looks unnecessary
public void printDay()
{
System.out.println("When printing, your day is " + day);
}
// return the next day
public String getNextDay()
{
// using direct comparison will fail as day == "Saturday"?
// so use compareTo() method...
if((day.compareTo("Saturday") == 0) || (day.compareTo("Sat") == 0))
return ("Sunday");
else if((day.compareTo("Sunday") == 0) || (day.compareTo("Sun") == 0))
return ("Monday");
else if((day.compareTo("Monday") == 0) || (day.compareTo("Mon") == 0))
return ("Tuesday");
else if((day.compareTo("Tuesday") == 0) || (day.compareTo("Tue") == 0))
return ("Wednesday");
else if((day.compareTo("Wednesday") == 0) || (day.compareTo("Wed") == 0))
return ("Thursday");
else if((day.compareTo("Thursday") == 0) || (day.compareTo("Thu") == 0))
return ("Friday");
else if((day.compareTo("Friday") == 0) || (day.compareTo("Fri") == 0))
return ("Saturday");
else
return ("\"Opps Error lol!\"");
}
// return the previous day
public String getPreDay()
{
if((day.compareTo("Friday") == 0) || (day.compareTo("Fri") == 0))
return ("Thursday");
else if((day.compareTo("Thursday") == 0) || (day.compareTo("Thu") == 0))
return ("Wednesday");
else if((day.compareTo("Wednesday") == 0) || (day.compareTo("Wed") == 0))
return ("Tuesday");
else if((day.compareTo("Tuesday") == 0) || (day.compareTo("Tue") == 0))
return ("Monday");
else if((day.compareTo("Monday") == 0) || (day.compareTo("Mon") == 0))
return ("Sunday");
else if((day.compareTo("Sunday") == 0) || (day.compareTo("Sun") == 0))
return ("Saturday");
else if((day.compareTo("Saturday") == 0) || (day.compareTo("Sat") == 0))
return ("Friday");
else
return ("\"Opps Error lol!\"");
}
// main execution point
public static void main (String args[])
{
// One of its weakness is the case sensitive: sun, Sunday, sunday, SuNdAy...
// need more codes to avoid this case sensitiveness...
// instantiate testday object of type MyDay class
// with "Sun" as initial value....
MyDay testday = new MyDay("Sun");
// prompt user to set his/her day
System.out.print("Enter day to set your day: ");
// read and store user's day
String storeday = readinput.nextLine();
// invoke setDay() method to set a day defined by user
testday.setDay(storeday);
// invoke getDay() method to get a day
System.out.println("Your day is " + testday.getDay());
// test printing by invoking printDay() method
testday.printDay();
// invoke getPreDay() method to get the previous day
System.out.println("Your previous day is " + testday.getPreDay());
// invoke getNextDay() method to get the next day
System.out.println("Your next day is " + testday.getNextDay());
}
}
A Sample outputs:
Enter day to set your day: Wednesday
Your day is Wednesday
When printing, your day is Wednesday
Your previous day is Tuesday
Your next day is Thursday
Enter day to set your day: Sat
Your day is Sat
When printing, your day is Sat
Your previous day is Friday
Your next day is Sunday
Enter day to set your day: sun
Your day is sun
When printing, your day is sun
Your previous day is "Opps Error lol!"
Your next day is "Opps Error lol!"
Enter day to set your day: Saturday
Your day is Saturday
When printing, your day is Saturday
Your previous day is Friday
Your next day is Sunday
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Well, that all for this part. To learn how C++ features and C++ itself been implemented in C++ .Net of Microsoft (and apply also to other .NET family such as VB .NET and C#) that comparable to Java, please jump to Visualcplusdotnet.com. Take note that, the Windows programming using Microsoft Foundation Class (MFC) already implemented the C++ object oriented principles. More Java programming and its open source programs can be found in Java GUI programming and its open source programs. However, the IDE used is NetBeans.
tenouk fundamental of C++ object oriented tutorial
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