Chapter 9 Exercise 11, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

(Algebra: 2 2 linear equations)
      Design a class named LinearEquation for a 2 2 system of linear equations:

      The class contains:
          ■ Private data fields a, b, c, d, e, and f.
          ■ A constructor with the arguments for a, b, c, d, e, and f.
          ■ Six getter methods for a, b, c, d, e, and f.
          ■ A method named isSolvable() that returns true if ad - bc is not 0.
          ■ Methods getX() and getY() that return the solution for the equation.

       Draw the UML diagram for the class and then implement the class.
       Write a test program that prompts the user to enter a, b, c, d, e, and f
       and displays the result. If ad - bc is 0, report that “The equation has no solution.”
       See Programming Exercise 3.3 for sample runs.

public class LinearEquation {

    private double a;
    private double b;
    private double c;
    private double d;
    private double e;
    private double f;

    public LinearEquation(double a, double b, double c, double d, double e, double f) {
        this.a = a;
        this.b = b;
        this.c = c;
        this.d = d;
        this.e = e;
        this.f = f;
    }

    public double getA() {
        return a;
    }

    public void setA(double a) {
        this.a = a;
    }

    public double getB() {
        return b;
    }

    public void setB(double b) {
        this.b = b;
    }

    public double getC() {
        return c;
    }

    public void setC(double c) {
        this.c = c;
    }

    public double getD() {
        return d;
    }

    public void setD(double d) {
        this.d = d;
    }

    public double getE() {
        return e;
    }

    public void setE(double e) {
        this.e = e;
    }

    public double getF() {
        return f;
    }

    public void setF(double f) {
        this.f = f;
    }

    public double getX() {
        return (e * d - b * f) / ab_Minus_bc();
    }


    public double getY() {
        return (a * f - e * c) / ab_Minus_bc();
    }


    /** If there is no solution the lines are parallel **/
    public boolean isSolvable(){
        return ab_Minus_bc() != 0;
    }

    private double ab_Minus_bc(){
        return a * d - b * c;
    }

    public static LinearEquation getIntersectingPoint(double x1,double y1,double x2,double y2,
                                                      double x3,double y3,double x4,double y4) {
        double a = (y1 - y2);
        double b = (-x1 + x2);
        double c = (y3 - y4);
        double d = (-x3 + x4);
        double e = -y1 * (x1 - x2) + (y1 - y2) * x1;
        double f = -y3 * (x3 - x4) + (y3 - y4) * x3;

        return new LinearEquation(a,b,c,d,e,f);
    }

    public static LinearEquation getIntersectingPoint(MyPoint p1, MyPoint p2, MyPoint p3, MyPoint p4) {
        return getIntersectingPoint(p1.x(), p1.y(), p2.x(), p2.y(),
                                    p3.x(), p3.y(), p4.x(), p4.y());
    }

    public static LinearEquation getIntersectingPoint(MyPoint[] p) {

        return getIntersectingPoint(p[0], p[1], p[2], p[3]);
    }

    public static LinearEquation getIntersectingPoint(double[][] points) {

        return getIntersectingPoint(points[0][0],points[0][1],points[1][0],points[1][1],
                                    points[2][0],points[2][1],points[3][0],points[3][1]);
    }

}

import java.util.Scanner;

public class Exercise_11 {

    public static void main(String[] strings) {

        Scanner input = new Scanner(System.in);

        System.out.print("Enter a, b, c, d, e, f: ");
        double a = input.nextDouble();
        double b = input.nextDouble();
        double c = input.nextDouble();
        double d = input.nextDouble();
        double e = input.nextDouble();
        double f = input.nextDouble();

        LinearEquation linear = new LinearEquation(a,b,c,d,e,f);

        if (linear.isSolvable()) {
            System.out.println("x is " + linear.getX() + " and y is " + linear.getY());
        } else {
            System.out.println("The equation has no solution.");
        }
    }

}