Complex.java

import java.util.Objects;

public class Complex {
    private final double re;
    private final double im;

    public Complex(double real, double imag) {
        re = real;
        im = imag;
    }

    public String toString() {
        if (im == 0) return re + "";
        if (re == 0) return im + "i";
        if (im <  0) return re + " - " + (-im) + "i";
        return re + " + " + im + "i";
    }

    public Complex plus(Complex b) {
        Complex a = this;             
        double real = a.re + b.re;
        double imag = a.im + b.im;
        return new Complex(real, imag);
    }

    public Complex minus(Complex b) {
        Complex a = this;
        double real = a.re - b.re;
        double imag = a.im - b.im;
        return new Complex(real, imag);
    }

    public Complex times(Complex b) {
        Complex a = this;
        double real = a.re * b.re - a.im * b.im;
        double imag = a.re * b.im + a.im * b.re;
        return new Complex(real, imag);
    }
    public Complex conjugate() {
        return new Complex(re, -im);
    }

    public double re() { return re; }
    public double im() { return im; }
}