public class ComplexNumber {
  public static void main(String args[]) {
    System.out.println("\nComplexNumber.main()"); 

    Complex 
      c1 = new Complex(1, 2),                // instantiate Complex numbers
      c2 = new Complex(2, 1);
    Number
      n1 = new Number(3),                    // instantiate ordinary numbers
      n2 = new Number(4);

    System.out.println(c1.plus(c2));         // apply plus to c1, giving it c2
                                             // plus returns a new Complex number, which has a toString()
    System.out.println(c1.minus(c2));
    System.out.println(c1.times(c2));
  
    System.out.println(n1.plus(n2));         // similar for ordinary numbers
    System.out.println(n1.minus(n2));
    System.out.println(n1.times(n2));
  
  }
}

class Complex {
  private double re, im;                     // Complex numbers have two parts
  public Complex(double re, double im) {     // constructor receives and stores the two parts
    this.re = re;
    this.im = im;
  }
  public double real() {                     // accessor methods
    return re;
  }
  public double imag() {
    return im;
  }
  public Complex plus(Complex c) {           // return a new Complex number based on the two parts
                                             // of "this" object, and the two parts of the parameter c.
    return new Complex(re + c.real(), im + c.imag());
  }
  public Complex minus(Complex c) {
    return new Complex(re - c.real(), im - c.imag());
  }
  public Complex times(Complex c) {
    return new Complex(re*c.real() - im*c.imag(), re*c.imag() + im*c.real());
  }
  public String toString() {                 // makes for easy printing of Complex numbers
    if (re!=0 && im>0) 
      return re +" + " + im + "i";
    if (re!=0 && im<0) 
      return re + " - " + (-im) + "i";
    if (im==0) 
      return String.valueOf(re);             // static call
    if (re==0) 
       return im + "i";
    return "Unknown";
  }       
}

class Number extends Complex {              // derived class, or subclass
  public Number(double n) {                 // constructor only needs one number
    super(n,0.0);                           // call parent's constructor with a default imaginary value
  }
}