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How to solve a Quadratic Equation in Java ?.

Updated on September 17, 2014

In this Java tutorial, you will learn how to solve Quadratic equation through a Java program. In this Java tutorial, you will encounter a video tutorial which will demonstrate how to solve Quadratic equation step-by-step. Below there is complete Java source code along with steps to implement the same. At last there is output of the program.

What is a Quadratic Equation ?.

Video tutorial - How to solve Quadratic Equation in Java ?.

Below is the video tutorial, which demonstrate how to solve Quadratic Equation in Java step-by-step.

// Step 1 - Import Scanner class from the package
// java.util. Before using Scanner class nextDouble
// method, you have to import Scanner class.
import java.util.Scanner;

public class QuadraticEquationDemo
{
	public static void main(String[] args)
	{
		// Step 2 - Create a Scanner class instance using
		// new operator and calling Scanner constructor.
		// The constructor takes in System.in inputstream
		// as a parameter to it. System.in helps Scanner
		// class to read user inputs from the Java console.
		Scanner input = new Scanner(System.in);

		// Step 3 - Create 5 variables of datatype double.
		// These variables take in values of constants used in 
		// quadratic equation such as - a , b , c , d ,discriminant.
		// All these variables are initialized to zero. These variables
		// hold values entered by the user later.
		double a = 0;
		double b = 0;
		double c = 0;
		double d = 0;
		double discriminant = 0;

		// Step 4 - Prompt the user to enter the value of constant a.
		System.out.print("Enter the value of constant a : "); 

		// Step 5 - a holds the value entered by the user on Java console.
		// Scanner class has a method by name nextDouble(). This method
		// reads double value entered by user on the Java console and 
		// assign it to a variable.
		a = input.nextDouble();

		// Step 6 - Prompt the user to enter the value of constant b.
		System.out.print("Enter the value of constant b : "); 

		// Step 7 - b holds the value entered by the user on Java console.
		// Scanner class has a method by name nextDouble(). This method
		// reads double value entered by user on the Java console and 
		// assign it to b variable.
		b = input.nextDouble();

		// Step 8 - Prompt the user to enter the value of constant c.
		System.out.print("Enter the value of constant c : "); 

		// Step 9 - c holds the value entered by the user on Java console.
		// Scanner class has a method by name nextDouble(). This method
		// reads double value entered by user on the Java console and 
		// assign it to c variable.
		c = input.nextDouble();

		// Step 10 - Calculate discriminant of quadratic equation by using
		// following formula - 
		// discriminant = (b * b - 4 * a * c)
		discriminant = (b * b - 4 * a * c);

		// Step 11 - Calculate the value of d by using following formula - 
		// d = square root of discriminant.
		// Math class has a static method by name sqrt(). This method 
		// returns square root of number passed to it as parameter.
		d = Math.sqrt(discriminant);

		// Step 12 - Here, if discriminant comes out to be greater than 
		// quadratic equation has two roots calculated by formula - 
		// roots = + ( -b + d ) / ( 2.0 * a ))
		// else roots of quadratic equation are not real numbers.
		if (discriminant >= 0.0) {
			System.out.println("First root of the Quadratic equation is : "
					+(-b + d) / (2.0*a));

			System.out.println("Second root of the Quadratic equation is : "
					+(-b - d) / (2.0*a));
		} 
		else 
		{
			System.out.println("The roots are not real numbers.");
		}
	}
}

Steps to implement -

Step 1 - Import Scanner class from the package java.util. Before using Scanner class nextDouble method, you have to import Scanner class.

Step 2 - Create a Scanner class instance using new operator and calling Scanner constructor. The constructor takes in System.in inputstream as a parameter to it. System.in helps Scanner class to read user inputs from the Java console.

Step 3 - Create 5 variables of datatype double. These variables take in values of constants used in quadratic equation such as - a , b , c , d ,discriminant. All these variables are initialized to zero. These variables hold values entered by the user later.

Step 4 - Prompt the user to enter the value of constant a.

Step 5 - 'a' holds the value entered by the user on Java console. Scanner class has a method by name nextDouble(). This method reads double value entered by user on the Java console and assign it to 'a' variable.

Step 6 - Prompt the user to enter the value of constant b.

Step 7 - 'b' holds the value entered by the user on Java console. Scanner class has a method by name nextDouble(). This method reads double value entered by user on the Java console and assign it to 'b' variable.

Step 8 - Prompt the user to enter the value of constant c.

Step 9 - 'c' holds the value entered by the user on Java console. Scanner class has a method by name nextDouble(). This method reads double value entered by user on the Java console and assign it to 'c' variable.

Step 10 - Calculate discriminant of quadratic equation by using
following formula -
discriminant = (b * b - 4 * a * c)

Step 11 - Calculate the value of d by using following formula -
d = square root of discriminant.
Math class has a static method by name sqrt(). This method returns square root of number passed to it as parameter.

Step 12 - Here, if discriminant comes out to be greater than quadratic equation has two roots calculated by formula -
roots = + ( -b + d ) / ( 2.0 * a ))
else roots of quadratic equation are not real numbers.



Output of the program -

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