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OBJECT ORIENTED PROGRAMMING:
FROM C++ TO JAVA AND C++ .NET
Java Compiler/IDE: JGRASP
Project: Just Java Old Plain Code
Project Settings: None, all default settings
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.....
}
}
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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(