Question

I’m using the Stanford version of Eclipse as I’m learning from one of their videos, and using their blank project template.

Basically, I’m writing a custom class “Fraction”. One of the constructors takes two numbers (doubles) and converts them to ints before storing them as numerator and denominator.

I’ve done

import java.lang.*;

public class Fraction {

And somewhere down I have

double numerator = Double(fractionComponents[0]); // fractionComponents is an array of string
double denominator = Double(fractionComponents[1]);

but I get the error:

The method Double(String) is undefined for the type Fraction.

I’ve also tried extending the class from Double.

Answer 1

You want to use the static parseDouble method, like so:

double numerator = Double.parseDouble(fractionComponents[0]);
double denominator = Double.parseDouble(fractionComponents[1]);

Note that you could also instantiate a Double, but you should prefer to use the static method as it leaves the possibility for the implemention to cache Double objects, and it’s more clear to the reader what is going on – you’re parsing a string for a double value.

If you were to use the constructor, it’s not immediately clear what the type of fractionComponents[0] is because there’s both a Double(String) and Double(double) constructor.