using math class in java

Question

I'm trying to calculate the power of a double to calculate the Quadratic Formula

Here is the code:

private Scanner sc;
double a, b, c;
// Input Coefficients
public void InputCoeff() {
    sc = new Scanner(System.in);

    System.out.println("Please enter the coefficients of this quadratic equation.");
    System.out.println("'ax2 + bx + c = 0'");
    System.out.print("a = ");
    a = sc.nextDouble();
    if(a == 0){
        System.out.println("Coefficient of x2 ('a') can't be zero.");
        System.out.println("Otherwise, it'll be a linear funciton.");
    }
    System.out.print("b = ");
    b = sc.nextDouble();
    System.out.print("c = ");
    c = sc.nextDouble();
}

public void SqRt(double x, double y, double z) {
    double sqrt;
    sqrt = pow(y, 2) - (4 * x * z); // This generates an error
    System.out.println();
}

Why this error?

Thanks.

Why do people up-vote questions without a clear error message? I gave a -1 and a vote to close; being able to state the error message/problem clearly - which is a *copy and paste operation here* - is an important skill to master. *Please don't up-vote questions unless there are deserving of it*. This question, with lack of error message and vague title is just garbage to future searches. — , Nov 04 '12 at 06:31
BTW, it's not very "Java-like" to declare variables first and assign to them later. You can simply do `double sqrt = someExpression`. — Sanjay T. Sharma, Nov 04 '12 at 06:44
@pst The title is related to the error (the line of code where I clearly state the error, in a comment). I knew the problem is related to the math class (pow(x,y)) & indeed it turned out to be so. — InspiringProgramming, Nov 04 '12 at 15:09
You didn't state *what the error was*. Hiding important information in a comment in the code isn't useful either. — user207421, Nov 04 '12 at 22:01

score 4 · Accepted Answer · edited Nov 04 '12 at 06:39

4

Change pow to Math.pow. The Math class is a static class, and you need to get the method from the class itself.

edited Nov 04 '12 at 06:39

Andro Selva

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answered Nov 04 '12 at 06:21

Brandon

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2

`pow` can work without prefixing it with `Math` if the OP uses static imports. – Sanjay T. Sharma Nov 04 '12 at 06:45

score 1 · Answer 2 · answered Nov 04 '12 at 06:22

Use Math. as prefix to your function pow because pow(double a, double b) is an static method from java.lang.Math class:

public void SqRt(double x, double y, double z) {
    double sqrt;
    sqrt = Math.pow(y, 2) - (4 * x * z); // This generates an error
    System.out.println(sqrt);
}

Also I think you may want to return sqrt from this method so change the return type from void to double and add a return statement in the end as below:

public dobule SqRt(double x, double y, double z) {
    double sqrt;
    sqrt = Math.pow(y, 2) - (4 * x * z); // This generates an error
    System.out.println(sqrt);
        return sqrt;
}

score 1 · Answer 3 · answered Nov 04 '12 at 08:43

Math.pow is a relative expensive operation to use and also longer to type in many case so I would avoid it if you can. It's much simpler (and faster for you and the computer) use x * x

public static Set<Double> solve(double a, double b, double c) {
    Set<Double> solutions = new TreeSet<Double>();
    double discriminant = b * b - 4 * a * c;
    solutions.add((-b - Math.sqrt(discriminant)) / (2 * a));
    solutions.add((-b + Math.sqrt(discriminant)) / (2 * a));
    solutions.remove(Double.NaN);
    return solutions;
}

public static void main(String... args) {
    System.out.println(solve(1, 3, 2));
    System.out.println(solve(1, 0, -1));
    System.out.println(solve(1, 4, 4));
    System.out.println(solve(1, 0, 1));
}

prints

[-2.0, -1.0]
[-1.0, 1.0]
[-2.0]
[]

Note that you can have none, one or two real solutions.

using math class in java

3 Answers3