在Java中使用复杂的类声明泛型变量

Question

I have a class to calculate with complex numbers, a real part and an imaginary part as double type. In other part I have a rational class to calculate rational numbers. Now I want that my complex class can operate when the real part and the imaginary part are rational numbers. I've read some docs about generics but I don't know how to declare real part and imaginary part as generic types and use methods as add 2 complex numbers when the real and imaginary parts are doubles or rationals. This is my test code:

import java.util.regex.Pattern;

public class Complex {
    private double real;
    private double imaginary;
    private Rational qreal;
    private Rational qimaginary;

    public Complex(double real, double imaginary) {
        super();
        this.real = real;
        this.imaginary = imaginary;
    }
    public Complex(Rational real, Rational imaginary) {
        this.qreal = real;
        this.qimaginary = imaginary;
    }
    public Complex(String z) {
        z = z.replaceAll(" ","");
        if(z.contains("i") || z.contains("j")){
            if(z.contains("+")) {
                String[] z1 = z.split(Pattern.quote("+"));
                this.real = Double.parseDouble(z1[0]);
                this.imaginary = Double.parseDouble(z1[1].substring(0, z1.length-1));
            }
            else if(z.contains("-")) {
                String[] z1 = z.split(Pattern.quote("-"));
                this.real = Double.parseDouble(z1[0]);
                this.imaginary = -Double.parseDouble(z1[1].substring(0, z1.length-1));
            }
            else System.out.println("Syntax Error");
        }
        else System.out.println("The complex must only contains i or j as imaginary unit");
    }
    public double getReal() {
        return real;
    }
    public void setReal(double real) {
        this.real = real;
    }
    public double getImaginary() {
        return imaginary;
    }
    public Rational getQreal() {
        return qreal;
    }
    public void setQreal(Rational qreal) {
        this.qreal = qreal;
    }
    public Rational getQimaginary() {
        return qimaginary;
    }
    public void setQimaginary(Rational qimaginary) {
        this.qimaginary = qimaginary;
    }
    public void setImaginary(double imaginary) {
        this.imaginary = imaginary;
    }

    Complex opposite(Complex z) {return new Complex(-z.real, -z.imaginary);}
    double abs() {return Math.hypot(this.real, this.imaginary);}
    Complex conjugate() {return new Complex(real, -imaginary);}
    Complex inverse() {
        if(this.real == 0 && this.imaginary == 0) return new Complex(Double.NaN, Double.NaN);
        else {
            Complex c = this.conjugate();
            double abs_square = Math.pow(this.abs(), 2.);
            return new Complex(c.real / abs_square, c.imaginary / abs_square);
        }
    }

    Complex add2(Complex z) {
        System.out.println("Suma " + this.qreal.add(z.qreal) + " " + this.qimaginary.add(z.qimaginary) + "i");
        return new Complex(this.qreal.add(z.qreal), this.qimaginary.add(z.qimaginary));
    }
    Complex add(Complex z) {return new Complex(this.real + z.real, this.imaginary + z.imaginary);}
    Complex subtract(Complex z) {return add(z.opposite(z));}
    Complex product(Complex z) {
        double r, i;
        r = this.real * z.real - this.imaginary * z.imaginary;
        i = this.real * z.imaginary + this.imaginary * z.real;
        return new Complex(r, i);
    }
    Complex div(Complex z) {
        Complex num = this.product(z.conjugate());
        double den = Math.pow(Math.hypot(z.real, z.imaginary), 2.);
        return new Complex(num.real / den, num.imaginary / den);
    }
    /* (non-Javadoc)
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        return "Complex [real=" + real + ", imaginary=" + imaginary + ", qreal=" + qreal + ", qimaginary=" + qimaginary
                + "]";
    }


    /*@Override
    public String toString() {
        if(imaginary > 0.) {
            if (imaginary == 1.)
                return real + " + " + "i";
            return real + " + " + imaginary + "i";
        }
        else if(imaginary < 0.) {
            if (imaginary == -1.)
                return real + " - " + "i";
            return real + " " + imaginary + "i";
        }
        else if(imaginary == 0.)
            return "" +  real;
        else if(real == 0.)
            return  imaginary + "i";
        else
            return "0";
    }*/



}

If you see the code I've implemented 2 add methods but i want only one,and so that for the other methods, toString() too.

Answer 1

Generics are useful when you want to preserve type information. But the generic type still needs to have some known interface in order to use it. Since double and Rational don't share common interface, it will not be possible to directly create a generic implementation that works for both types.

What you could do is create an interface Complex with 2 implementations, DoubleComplex and RationalComplex :

public interface Complex<T> {

    T getReal();
    T getImaginary();

    Complex<T> opposite(Complex<T> z);
    double abs();
    Complex<T> conjugate();
    Complex<T> inverse();

    Complex<T> add(Complex<T> z);
    Complex<T> subtract(Complex<T> z);
    Complex<T> product(Complex<T> z);
    Complex<T> div(Complex<T> z);

}

public class DoubleComplex implements Complex<Double> {

    private final double real;
    private final double imaginary;

    ...

    @Override
    public Complex<Double> add(Complex<Double> z) {
        return new DoubleComplex(this.real + z.getReal(), this.imaginary + z.getImaginary());
    }

    ...
}

public class RationalComplex implements Complex<Rational> {

    private final Rational real;
    private final Rational imaginary;

    ...

    @Override
    public Complex<Rational> add(Complex<Rational> z) {
        return new RationalComplex(this.real.add(z.getReal()), this.imaginary.add(z.getImaginary()));
    }

    ...
}