Error while comparing two methods

Question

So I'm trying to do a simple program that can find the module of a Complex Number using generics and compares two modules:

public class ComplexNumber <T extends Number,U extends Number>
    implements Comparable<ComplexNumber<T, U>>
{
    private T real;
    private U imaginary;

    public ComplexNumber(T real, U imaginary)
    {
        this.real=real;
        this.imaginary=imaginary;
    }

    public T getReal()
    {
        return real;
    }

    public int compareTo(ComplexNumber<?, ?> o)
    {
        return this.modul().compareTo(o.modul());
    }

    public U getImaginary()
    {
        return imaginary;
    }

    public double modul()
    {
        double c=Math.sqrt(real.doubleValue()*real.doubleValue()+imaginary.doubleValue()*imaginary.doubleValue());
        return c;
    }

    public String toString()
    {
        return String.format("%.2f+%.2fi", real.doubleValue(), imaginary.doubleValue());
    }
}

However it gives me two real time errors one in the .compareTo function stating:"Cannot invoke compareTo(double) on the primitive type double"

and one in the beginning of the class: "Multiple markers at this line - The type ComplexNumber must implement the inherited abstract method Comparable>.compareTo(ComplexNumber) - The type ComplexNumber must implement the inherited abstract method "

Answer 1

you're looking for something along the lines of:

@Override
public int compareTo(ComplexNumber<T, U> o) {
        // logic
}

edit

if you definitely need to use wildcards then you'll need to change the class declaration to:

class ComplexNumber <T extends Number,U extends Number> implements Comparable<ComplexNumber<?, ?>>

in which case you can leave the compareTo method signature as is.

regarding the first error you've received, this is because you're trying to call the compareTo method on a primitive type double which would not work at all. To solve the problem, you'd want to use Double.compare and pass in the appropriate data.

@Override
public int compareTo(ComplexNumber<?, ?> o) {
       return Double.compare(modul(), o.modul());
}