Question

I can not understand my mistake in this code, it will compile if I write new Cosine(); but fails if I write new Cosine(x);

import java.lang.Object;
import java.lang.Math;

class Cosine {
    double Cosine (double x) {
    double result = Math.cos(Math.toRadians(x));
    return result;
  }
}

public class test {
     public static void main (String[] args){
     double x = 90;
     new Cosine(x);
  }
}   

Answer 1

You haven’t given Cosine a constructor that takes a double. Try this:

class Cosine {

    public final double result; //field holding the result

    //constructor
    public Cosine (double x){
     result = Math.cos(Math.toRadians(x)); //compute the result
   }
}

public class test {
    public static void main (String[] args){
        double x = 90;
        double cosX = new Cosine(x).result;
    }
}

Although this raises the question why a simple static method couldn’t be used:

public static double getCosine(double x) {
    return Math.cos(Math.toRadians(x));
}

public class test {
    public static void main (String[] args){
        double x = 90;
        double cosX = getCosine(x);
    }
}

This doesn’t require the instantiation of a Cosine object for every computation.