[Java] Quadratic Equation Solver


/*
* ==========================================================================
* This Java Program prompts a user for coefficients in a quadratic equation,
* and computes and prints the roots of the equation.
*
* Written By : Nathan Blattau and Mark Austin July, 1997
* ==========================================================================
*/

import java.lang.Math;
import java.util.*;
import java.io.*;

class Quadratic {

public static void main( String args[] ) {

float fA,fB,fC;
float fRoot1, fRoot2;
float fDiscriminant;
String sLine;

// Print welcome message.

System.out.println("Welcome to The Quadratic Equation Solver");
System.out.println("----------------------------------------");

// Prompt user for coefficients in quadratic equation.

System.out.println("Please Enter coefficients for equation");
System.out.println("a.x^2 + b.x + c");

System.out.println("Coefficent a : ");
sLine = keyboardInput();
fA = Float.valueOf(sLine).floatValue();

System.out.println("Coefficent b : ");
sLine = keyboardInput();
fB = Float.valueOf(sLine).floatValue();

System.out.println("Coefficent c : ");
sLine = keyboardInput();
fC = Float.valueOf(sLine).floatValue();

// Print details of quadratic equation to screen.

System.out.println("The equation you have entered is : ");
System.out.println(+fA+".x^2 + "+fB+".x + "+fC);

// Check for degenerate roots (i.e., fA = fB = zero).

if ( fA==0 && fB==0 ) {
System.out.println("Cannot solve " + fC +" = 0.0");
return;
}

if ( fA==0 && fB !=0 ) {
fRoot1 = -fC/fB;
System.out.println("Degenerate root : Root = "+ fRoot1);
return;
}

// Compute discriminant of quadratic equation.

fDiscriminant = fdiscriminant(fA,fB,fC);

// Case for two real roots.

if ( fDiscriminant >= 0.0 ) {

fRoot1 = (float)(-fB/2.0/fA-(float)Math.sqrt(fDiscriminant) /
2.0 / fA );
fRoot2 = (float)(-fB/2.0/fA+(float)Math.sqrt(fDiscriminant) /
2.0 / fA);

System.out.println("Two real roots : Root1 : " + fRoot1);
System.out.println(" Root2 : " + fRoot2);
return;
}

// Two complex roots

fRoot1 = (float) (-fB/2.0/fA);
fRoot2 = (float) (Math.sqrt(-fDiscriminant)/2.0/fA);

System.out.println("Two complex roots");
System.out.println("Root1 : " + fRoot1 + "+" + fRoot2 + "i");
System.out.println("Root2 : " + fRoot1 + "-" + fRoot2 + "i");
}

/*
* =============================================================
* Method fdiscriminant() : compute discriminant of quadratic
*
* Input : fA, fB, and fC -- coefficients in quadratic equation
* Output : float fReturn -- discriminant of quadratic equation
* =============================================================
*/

static float fdiscriminant(float fA, float fB, float fC) {
float fReturn;

fReturn= (float)(fB*fB-4.0*fA*fC);
return fReturn;
}

/*
* ===========================================================
* Method keyboardInput() : Get line of input from keyboard
*
* Input : None.
* Output : String sLine -- character string of keyboard input
* ===========================================================
*/

static String keyboardInput() {
String sLine;

DataInputStream in = new DataInputStream(System.in);
try{
sLine = in.readLine();
return sLine;
}
catch (Exception e){
return "error";
}
}
}


[REF]http://www.isr.umd.edu/~austin/
[REF]http://www.isr.umd.edu/~austin/book.d/code.d/java.d/Quadratic.java