Chapter 13, Problem 13.1PE

(Triangle class) Design a new Triangle class that extends the abstract GeometricObject class. Draw the UML diagram for the classes Triangle and GeometricObject then implement the Triangle class. Write a test program that prompts the user to enter three sides of the triangle, a color, and a Boolean value to indicate whether the triangle is filled. The program should create a Triangle object with these sides, and set the color and filled properties using the input. The program should display the area, perimeter, color, and true or false to indicate whether it is filled or not.

Program Plan Intro

Program to create Triangle class

Program Plan:

• Include a class name named “Exercise_13_01”.
  • Include the scanner package.
  • Declare the main() function.
  • Create a scanner object.
  • Prompt the user to enter three sides of the triangle.
  • Prompt the user to enter a color.
  • Prompt the user to enter a Boolean value on whether the triangle is filled.
  • Create triangle object with the entered user input.
  • Set color and set filled in the triangle.
  • Print the output.
  • Close the main() function.
  • Close the class “Exercise_13_01”.
• Include an abstract class “GeometricObject”.
  • Declare all the data types of the variables.
  • Construct a default geometric object.
  • Construct a geometric object with color and filled value.
  • Assign color and fill to the object.
  • Set a new color.
  • Define an isFilled method returns filled and since filled is Boolean; the get method is named isFilled.
  • Set a new filled and getDateCreated method.
  • Override toString function to return output.
  • Define Abstract method getArea.
  • Define Abstract method getPerimeter.
  • Close class.
• Include a class “Triangle” that extends the class GeometricObject.
  • Declare the three sides of the triangle.
  • Include a triangle constructor.
  • Assign values to all three sides of the triangle.
  • Assign triangle values to all attributes.
  • Return side1 and Set side1 to a new length.
  • Return side2 and Set side2 to a new length.
  • Return side3 and Set side3 to a new length.
  • Create a Function to return area of the Triangle.
  • Create a function to return a string description of the object.
  • Close class.

Program Description Answer

The java code to design a new Triangle class that extends the abstract GeometricObject class and to design a test program   that prompts the user to enter three sides of the triangle, a color, and a Boolean value to indicate whether the triangle is filled or not.

Explanation of Solution

Program:

File name: Exercise_13_01.java

//package to have user input

import java.util.Scanner;

//class Definition

public class Exercise_13_01

{

// Main method

public static void main(String[] args)

{

// Create a Scanner object

Scanner input = new Scanner(System.in);

/* Prompt the user to enter three sides of the triangle */

System.out.print("Enter three side of the triangle: ");

double side1 = input.nextDouble();

double side2 = input.nextDouble();

double side3 = input.nextDouble();

// Prompt the user to enter a color

System.out.print("Enter a color: ");

String color = input.next();

/*Prompt the user to enter a boolean value on whether the triangle is filled*/

System.out.print("Is the triangle filled (true / false)? ");

boolean filled = input.nextBoolean();

/* Create triangle object with the entered user input */

Triangle triangle = new Triangle(side1, side2, side3);

// set color

triangle.setColor(color);

// set filled

triangle.setFilled(filled);

// print the output

System.out.println(triangle.toString());

System.out.println("Area: " + triangle.getArea());

System.out.println("Perimeter: " + triangle.getPerimeter());

System.out.println("Color: " + triangle.getColor());

System.out.println("Triangle is" + (triangle.isFilled() ? "" : " not ")

+ "filled");

}

}

Filename: GeometricObject.java

//abstract class GeometricObject definition

public abstract class GeometricObject

{

//data type declaration

private String color = "while";

private boolean filled;

private java.util.Date dateCreated;

// Construct a default geometric object

protected GeometricObject()

{

dateCreated = new java.util.Date();

}

/* Construct a geometric object with color and filled value */

protected GeometricObject(String color, boolean filled)

{

dateCreated = new java.util.Date();

//assign color and fill

this.color = color;

this.filled = filled;

}

// Return color

public String getColor()

{

return color;

}

// Set a new color

public void setColor(String color)

{

this.color = color;

}

/* isFilled method returns filled and Since filled is boolean,the get method is named isFilled */

public boolean isFilled()

{

return filled;

}

// Set a new filled

public void setFilled(boolean filled)

{

this.filled = filled;

}

// Get dateCreated

public java.util.Date getDateCreated()

{

return dateCreated;

}

//override toString function to return output

@Override

public String toString()

{

return "created on " + dateCreated + "\ncolor: " + color +

" and filled: " + filled;

}

// define Abstract method getArea

public abstract double getArea();

//Define Abstract method getPerimeter

public abstract double getPerimeter();

}

Filename: Triangle.Java

/*Class definition of Triangle that extends the class GeometricObject */

public class Triangle extends GeometricObject

{

//declare the three sides of the triangle

private double side1;

private double side2;

private double side3;

//triangle constructor

public Triangle()

{

}

//assign values to all three sides of the triangle

public Triangle(double side1, double side2, double side3)

{

this.side1 = side1;

this.side2 = side2;

this.side3 = side3;

}

//assign triangle values to all attributes

public Triangle(double side1, double side2, double side3, String color, boolean filled)

{

this(side1, side2, side3);

setColor(color);

setFilled(filled);

}

// Return side1

public double getSide1()

{

return side1;

}

// Set side1 to a new length

public void setSide1(double side1)

{

this.side1 = side1;

}

// Return side2

public double getSide2()

{

return side2;

}

// Set side2 to a new length

public void setSide2(double side2)

{

this.side2 = side2;

}

// Return side3

public double getSide3()

{

return side3;

}

// Set side3 to a new length

public void setSide3(double side3)

{

this.side3 = side3;

}

// Function to Return area of the Triangle

@Override

public double getArea()

{

double s = (side1 + side2 + side3) / 2;

return Math.sqrt(s * (s - side1) * (s - side2) * (s - side3));

}

/* override function to Return perimeter of the triangle */

@Override

public double getPerimeter()

{

return side1 + side2 + side3;

}

/*override function to Return a string description of the object*/

@Override

public String toString()

{

return super.toString() + "\nArea: " + getArea() + "\nPerimeter: " + getPerimeter();

}

}

UML Diagram:

Explanation:

• Here, GeometricObject is an abstract class that extends the triangle class which is represented using an arrow. The triangle class then contains a rectangle that represents the objects used to input the three sides of the triangle.
• The remaining part is used to represent all the methods and functions used in the triangle class.
• The Triangle() method creates a triangle with default sides.  The method Triangle(side1:double, side2; double,side3;double) creates a triangle of the specified sides.
• Then the respective sides of the triangles are returned using getSide() methods.
• Then the method getArea() returns the area of the triangle and the method getPerimeter() returns the perimeter of the triangle and the function toString() returns a string description of the object.

Sample Output

Enter three side of the triangle: 3

4

5

Enter a color: red

Is the triangle filled (true / false)? false

created on Sun Jul 08 13:24:03 IST 2018

color: red and filled: false

Area: 6.0

Perimeter: 12.0

Area: 6.0

Perimeter: 12.0

Color: red

Triangle is not filled