Design and develop a Java program that continuously computes and
displays value(s) for x, given quadratic equations (i.e. a
second-order polynomials) of the form:

ax2 + bx + c = 0 
where the values for the coefficients a, b and c are supplied by the
user, and are assumed to be integers within the range of -100 to 100.
To control the loop use a menu interface. The menu should include two
options: "Calculate quadratic" and "End".

Note that to solve a quadratic equation we must calculate the roots.
This can be done using the quadratic formula:

root 1 = (-b + sqrt(b2-4ac)) / 2a

root2 = (-b - sqrt(b2-4ac)) / 2a

Example:

x2 + 2x - 8 = 0 
a= 1, b = 2, c = -8 
 
roots = (-2 +or- sqrt(22-4x1x-8)) / 2x1 
      = (-2 +or- sqrt(4+32)) / 2 
root1 = (-2 + 6)/2 = 4/2 = 2.0 
root2 = (-2 - 6)/2 = -8/2 = -4.0 
 
x = 2.0 or -4.0 

However, there are certain special consideration to be taken into account:

If a and b are both zero there is no solution (this is referred to as
the degenerate case):
-8 = 0?
a= 0, b = 0, c = -8
(degenerate case)

If a is zero and b is non zero the equation becomes a linear equation.

2x - 8 = 0
a= 0, b = 2, c = -8
(Linear equation)

root = -c/b = 8/2 = 4.0
x = 4.0

If the value for the term b2 - 4ac (the discriminant) is negative
there is no solution (conventionally we cannot find the square root of
a negative number!):
x2 + 2x + 8 = 0
a= 1, b = 2, c = 8

roots = (-2 +or- sqrt(22-4x1x8)) / 2x1
      = (-2 +or- sqrt(4-32)) / 2
      = (-2 +or- sqrt(-28))
Negative discriminant therefore no solution.

If the discriminant is 0 then there are two identical solutions, i.e.
only one solution (root) need be calculated:
x2 + 4x + 4 = 0
a= 1, b = 4, c = 4

roots = (-4 +or- sqrt(42-4x1x4)) / 2x1
      = (-4 +or- sqrt(16-16)) / 2
(Discriminant = 0, there fore only one solution)
root = -4/2 = -2
x = -2.0

Output, where appropriate, should be accurate to at least several decimal places.

Please try to include explanations where appropriate.

---

Clarification of Question by java_design-ga on 29 Nov 2005 05:39 PST

The program must be written in Java 1.5 !!!

I'd do it for $200.  I wouldn't do it for $15.

import	java.io.*;
public class quadratic
{
    public int a = 0,b = 0,c = 0;
    public int flag=0;
    public double r1=0,r2=0;
    public quadratic()
    {
        do
        {
            
        System.out.println("\n\n\n\n\nType 1 to Calculate quadratic equation");
        System.out.println("Type 3 to END");
        int choice = getChoice();
        
        switch(choice)
        {
        case 1:
        a = inputABC("a");
        b = inputABC("b");
        c = inputABC("c");

        if((Math.pow(b,2)-4*a*c)<0)
        {System.out.println("\nNegative discriminant therefore no solution!");}
        else if((Math.pow(b,2)-4*a*c)==0)
        {
        r1 = getRoot1(a,b,c);
        System.out.print("x= "+r1);   
        }
        else if(a==0&&b==0)
        {System.out.println("\nDegenerate Case");}
        else if(a==0)
        {double u = -c/b;
         System.out.println("The root is "+u);}
        else
        {
        r1 = getRoot1(a,b,c);
        r2 = getRoot2(a,b,c);
        System.out.print("x= "+r1+" or "+r2);
        }
        break;
        case 3:
        flag = 1;
        break;
        default:
        System.out.println("\nThat is not an option!  Try Again.");
        break;
        }
          
        }while(flag==0);
    }
    
    public int inputABC(String s2)
    {
        InputStreamReader stdin =
				new InputStreamReader(System.in);
		BufferedReader console =
				new BufferedReader(stdin);
		int i1=0;
		String	s1;
		try
		{
			System.out.print("Enter interger for "+s2+": ");
			s1 = console.readLine();
			i1 = Integer.parseInt(s1);
		}
		catch(IOException ioex)
		{
			System.out.println("\nInput error");
			System.exit(1);
		}
		catch(NumberFormatException nfex)
		{
			System.out.println("\"" + 
				nfex.getMessage() + 
				"\" is not numeric");
			System.exit(1);
		}
		return(i1);
    }
    public int getChoice()
    {
        InputStreamReader stdin =
				new InputStreamReader(System.in);
		BufferedReader console =
				new BufferedReader(stdin);
		int i2=0;
		String	s2;
		try
		{
			System.out.print("User's Choice: ");
			s2 = console.readLine();
			i2 = Integer.parseInt(s2);
		}
		catch(IOException ioex)
		{
			System.out.println("Input error");
			System.exit(1);
		}
		catch(NumberFormatException nfex)
		{
			System.out.println("\"" + 
				nfex.getMessage() + 
				"\" is not numeric");
			System.exit(1);
		}
		return(i2);
    }
    public double getRoot1(int x, int y, int z)
    {
        double root1 = (-y + Math.sqrt((Math.pow(b,2))-(4*x*z)))/(2*x);
        return(root1);
    }
        public double getRoot2(int x, int y, int z)
    {
        double root2 = (-y - Math.sqrt((Math.pow(b,2))-(4*x*z)))/(2*x);
        return(root2);
    }
     public static void main(String[] args)
    {
        quadratic qd = new quadratic();
    }
    
}