Chapter 13 Exercise 1, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

13.1 (Triangle class)
Design a new Triangle class that extends the abstract GeometricObject class.
Draw the UML diagram for the classes Triangle and GeometricObject and 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.

public class Triangle extends GeometricObject {

    private double side1;
    private double side2;
    private double side3;


    public Triangle(double side1, double side2, double side3) throws IllegalTriangleException {
        this.side1 = side1;
        this.side2 = side2;
        this.side3 = side3;
        isValidTriangle();
    }

    public Triangle() {
        this.side1 = 1;
        this.side2 = 1;
        this.side3 = 1;
    }

    @Override
    public double getArea() {

        double s = (side1 + side2 + side3) / 2.0;
        return Math.pow(s * (s - side1) * (s - side2) * (s - side3), 0.5);
    }

    @Override
    public double getPerimeter() {
        return side1 + side2 + side3;
    }

    @Override
    public String toString() {
        return "Triangle{" +
                "side1=" + side1 +
                ", side2=" + side2 +
                ", side3=" + side3 +
                '}';
    }

    public static boolean isTriangle(double side1, double side2, double side3) {

        return  ((side1 + side2 > side3) &&
                (side1 + side3 > side2) &&
                (side3 + side2 > side1));

    }

    public double getSide1() {
        return side1;
    }

    public void setSide1(double side1) throws IllegalTriangleException {
        this.side1 = side1;
        isValidTriangle();
    }

    public double getSide2() {
        return side2;
    }

    public void setSide2(double side2) throws IllegalTriangleException{
        this.side2 = side2;
        isValidTriangle();
    }

    public double getSide3() {
        return side3;
    }

    public void setSide3(double side3) throws IllegalTriangleException {
        this.side3 = side3;
        isValidTriangle();
    }

    private void isValidTriangle() throws IllegalTriangleException{
        if (!isTriangle(side1, side2, side3)) {
            throw new IllegalTriangleException(side1, side2, side3);
        }
    }

    public class IllegalTriangleException extends IllegalArgumentException {

        private double s1;
        private double s2;
        private double s3;

         public IllegalTriangleException(double s1, double s2, double s3) {
            super("Not a real triangle:" + " side1 = " + s1 + " side2 = " + s2 + " side3 = " + s3);
            this.s1 = s1;
            this.s2 = s2;
            this.s3 = s3;
        }

        public double getS1() {
            return s1;
        }

        public double getS2() {
            return s2;
        }

        public double getS3() {
            return s3;
        }


    }
}

import java.util.Scanner;

public class Exercise_01 {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        System.out.print("Enter three sides of a triangle: ");
        double[] sides = new double[3];
        for (int i = 0; i < sides.length; i++) {
            sides[i] = input.nextDouble();
        }
        System.out.print("Enter a triangle color: ");
        String color = input.next();
        System.out.print("Is the triangle filled? true/false: ");
        String isFilledString = input.next();
        boolean isFilled = (isFilledString.equals("true"));

        Triangle t1 = new Triangle(sides[0], sides[1], sides[2]);
        t1.setColor(color);
        t1.setFilled(isFilled);
        System.out.println("Triangle 1:");
        System.out.println("Area = " + t1.getArea());
        System.out.println("Perimeter = " + t1.getPerimeter());
        System.out.println("Color = " + t1.getColor());
        System.out.println("Is filled? " + t1.isFilled());


    }

}