CODEWITHSUNDEEP
java
August Rush
August Rush

Reputation: 1

implementing methods with parameters in java

I'm a new java programmer and I'm trying to write a program that finds the roots of a quadratic equation by implementing the roots() method in this class.

I think I've figured out how to implement the equation, but the return statement says: Error-Type mismatch: cannot convert from double to Set

How would I fix this error?

Thank You!

 package warmup;

import java.util.Set;

 public class Quadratic {

/**
 * Find the integer roots of a quadratic equation, ax^2 + bx + c = 0.
 * @param a coefficient of x^2
 * @param b coefficient of x
 * @param c constant term.  Requires that a, b, and c are not ALL zero.
 * @return all integers x such that ax^2 + bx + c = 0.
 */
public static Set<Integer> roots(int a, int b, int c) {

    //my code so far
    double q = -b + (Math.sqrt(Math.pow(b, 2)-4*a*c)/2*a);  
    return q;
}


/**
 * Main function of program.
 * @param args command-line arguments
 */
public static void main(String[] args) {
    System.out.println("For the equation x^2 - 4x + 3 = 0, the possible solutions are:");
    Set<Integer> result = roots(1, -4, 3);
    System.out.println(result);
  }


}

Upvotes: 0

Views: 174

Answers (6)

knownUnknown
knownUnknown

Reputation: 909

Why are you using Set<Integer> as the return type, instead you can use Double. Replace Set<Integer> with Double and your problem is solved.

Note:- You are trying to return double , but your method return type is Set ....

Upvotes: 0

Rishabh Maurya
Rishabh Maurya

Reputation: 1523

    import java.util.Set;
   import java.util.HashSet;

     public class Quadratic {

/**
 * Find the integer roots of a quadratic equation, ax^2 + bx + c = 0.
 * @param a coefficient of x^2
 * @param b coefficient of x
 * @param c constant term.  Requires that a, b, and c are not ALL zero.
 * @return all integers x such that ax^2 + bx + c = 0.
 */
    public static Set<Double> roots(int a, int b, int c) {
    Set<Double> result=new HashSet<>();
    //my code so far
     double p = (-b - (Math.sqrt(Math.pow(b, 2)-4*a*c)))/2*a;  
    result.add(p);
    double q = (-b + (Math.sqrt(Math.pow(b, 2)-4*a*c)))/2*a;  
    result.add(q);
    return result;
}


/**
 * Main function of program.
 * @param args command-line arguments
 */
public static void main(String[] args) {
    System.out.println("For the equation x^2 - 4x + 3 = 0, the possible solutions are:");
    Set<Double> result = roots(1, -4, 3);
    System.out.println(result);
  }


}

Upvotes: 0

Arthur Dent
Arthur Dent

Reputation: 795

The return type of your method is Set<Integer>. Returning a Set means that you can return zero, one, or more elements. This is appropriate since a quadratic equation has multiple roots in the general case.

<Integer> means that the elements of the set you are returning must be Integers, which is strange since roots of a quadratic equation are often real numbers and are sometimes complex numbers. I'd guess what you really want is Set<Double>.

If you really do want to return a single element, you will need to do so by returning a set to which you've added the root in question. Calling Collections.singleton() is a convenient way to do this.

Worthwhile reading:

https://docs.oracle.com/javase/6/docs/api/java/util/Set.html

https://docs.oracle.com/javase/6/docs/api/java/util/Collections.html#singleton(T)

Upvotes: 1

Nir Alfasi
Nir Alfasi

Reputation: 53565

The following code contains a few fixes to the code in the question, see the comments in the code for further explanation:

public static Set<Double> roots(int a, int b, int c) {
    Double x = Math.sqrt(Math.pow(b, 2) - 4 * a * c);
    Set<Double> result = new HashSet<>(); // return a set that contains the results
    result.add((-b + x)/ 2 * a); // -b should be divided by 2a as well
    result.add((-b - x)/ 2 * a); // -b should be divided by 2a as well
    return result;
}

public static void main(String[] args) {
    System.out.println("For the equation x^2 - 4x + 3 = 0, the possible solutions are:");
    Set<Double> result = roots(1, -4, 3); // the returned type is Set<Double> not Set<Integer> 
    System.out.println(result);
}

OUTPUT

For the equation x^2 - 4x + 3 = 0, the possible solutions are:
[1.0, 3.0]

Upvotes: 2

Penman
Penman

Reputation: 173

You're returning a double variable instead of a Set object in the roots function. Hence the type mismatch. Modify it as:

public static double roots(int a, int b, int c) {

double q = -b + (Math.sqrt(Math.pow(b, 2)-4*a*c)/2*a);  
return q;
}

Make sure to obtain the result of this function as a double as well. Change this:

 Set<Integer> result = roots(1, -4, 3);

to:

double result = roots(1, -4, 3);

This should work.

Upvotes: 0

jobair ahmed
jobair ahmed

Reputation: 121

public class Quadratic  {

public static double roots(int a, int b, int c) {

    //my code so far
    double q = -b + (Math.sqrt(Math.pow(b, 2)-4*a*c)/2*a);  
    return q;
}
public static void main(String[] args) {
    System.out.println("For the equation x^2 - 4x + 3 = 0, the possible solutions are:");
    double result = roots(1, -4, 3);
    System.out.println(result);
  }

}

Upvotes: 0

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