Complex number calculation

Question

Hello everyone!
I am working on this code to compute complex numbers (a+-bi) and I am a little stuck - I get an error message:
<<<invalid method declaration; return type required>>>public ComplexN( double re, double im)>>>>
Please, can anyone help me.
public class Complex {
    private double real = 0.0;
    private double imaginary = 0.0;
    public Complex() { this( 0, 0 );}
    double r = real;
    double i = imaginary;
    public ComplexN( double re,  double im) { this(re,im);}
    public Complex add( Complex a, Complex b ) { return  new Complex(a.r + b.r, a.i + b.i);}
    public Complex subtract( Complex a, Complex b ) { return new Complex(a.r - b.r, a.i - b.i);}
    public String toString() {return String.format( "(%.1f, %.1f)", real, imaginary );}
    Object[] add(Complex b) {return null;}
    Object[] subtract(Complex b) {return null;}
==================================================
public class ComplexTest
   public static void main( String args[] )
      Complex a = new Complex( 9.5, 7.7 );
      Complex b = new Complex( 1.2, 3.1 );
      System.out.printf( "a = %s\n", a );
      System.out.printf( "b = %s\n", b );
      System.out.printf( "a + b = %s\n", a.add( b ) );
      System.out.printf( "a - b = %s\n", a.subtract( b ) );
}

Answer 1

If you take the N off the name, you get this:
public Complex( double re,  double im) {
  this(re,im);
}OK, now walk through an instantiation like this:
Complex c = new Complex(1.0, 1.0);You call that constructor. And that constructor then delegates to the constructor that takes two double arguments. That is, it delegates to itself.
So it would just go on delegating to itself for eternity. This is bad.